KOHLER CH18-CH25 Genuine Maintenance Kit User Manual

CH18-CH25 Genuine Maintenance Kit

Product Information

The CH18-CH25, CH620-CH730, CH740, CH750 Service Manual provides
important safety precautions, maintenance instructions,
specifications, tools and aids, troubleshooting guidelines, and
disassembly/reassembly procedures for Kohler engines. The manual
covers various engine models and is available in Revision O. The
manual can be accessed online at KohlerEngines.com.

Product Usage Instructions

Before operating equipment powered by the Kohler engine, read
all safety precautions and instructions carefully. Refer to the
equipment’s operating instruction manual for specific usage
guidelines. Ensure that the engine is stopped and level before
performing any maintenance or service.

WARNING: Gasoline is extremely flammable and explosive.
Do not fill fuel tanks while the engine is hot or running. Store
gasoline only in approved containers in well-ventilated, unoccupied
buildings away from sparks or flames. Avoid using gasoline as a
cleaning agent.

WARNING: Rotating parts can cause severe injury. Stay
away from the engine while it’s in operation. Keep hands, feet,
hair, and clothing away from all moving parts to prevent injury.
Never operate the engine with covers, shrouds, or guards
removed.

WARNING: Carbon monoxide can cause severe nausea,
fainting, or death. Avoid inhaling exhaust fumes. Never run the
engine indoors or in enclosed spaces. The engine exhaust gases
contain poisonous carbon monoxide, which is odorless and
colorless.

WARNING: Accidental starts can cause severe injury or
death. Disconnect and ground spark plug lead(s) before
servicing.

WARNING: Hot parts can cause severe burns. Do not touch
the engine while it’s operating or just after stopping. Never
operate the engine with heat shields or guards removed.

WARNING: Cleaning solvents can cause severe injury or
death. Use only in well-ventilated areas away from ignition
sources. Carburetor cleaners and solvents are extremely flammable.
Follow cleaner manufacturer’s warnings and instructions on their
proper and safe use. Never use gasoline as a cleaning agent.

CAUTION: Electrical shock can cause injury. Do not touch
wires while the engine is running.

CAUTION: Damaging crankshaft and flywheel can cause
personal injury. Using improper procedures can lead to broken
fragments, which could be thrown from the engine. Always observe
and use precautions and procedures when installing flywheel.

CAUTION: Failure to utilize or reassemble debris screen
as designed could result in debris screen failure and serious
personal injury.

WARNING: Uncoiling spring can cause severe injury. Wear
safety goggles or face protection when servicing retractable
starter. Retractable starters contain a powerful, recoil spring
that is under tension. Always wear safety goggles when servicing
retractable starters and carefully follow instructions in
Retractable Starter for relieving spring tension.

Following these safety precautions and usage instructions can
help ensure safe and efficient operation of the Kohler engine.

CH18-CH25, CH620-CH730, CH740, CH750 Service Manual

IMPORTANT: Read all safety precautions and instructions carefully before operating equipment. Refer to operating instruction of equipment that this engine powers.
Ensure engine is stopped and level before performing any maintenance or service.

2 Safety 3 Maintenance 5 Specifications 15 Tools and Aids 18 Troubleshooting 23 Air Cleaner/Intake 24 Fuel System 37 Governor System 55 Lubrication System 57 Electrical System 76 Starter System 85 Clutch 87 Disassembly/Inspection and Service 102 Reassembly

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Safety

SAFETY PRECAUTIONS WARNING: A hazard that could result in death, serious injury, or substantial property damage. CAUTION: A hazard that could result in minor personal injury or property damage.
NOTE: is used to notify people of important installation, operation, or maintenance information.

WARNING
Explosive Fuel can cause fires and severe burns.
Do not fill fuel tank while engine is hot or running.
Gasoline is extremely flammable and its vapors can explode if ignited. Store gasoline only in approved containers, in well ventilated, unoccupied buildings, away from sparks or flames. Spilled fuel could ignite if it comes in contact with hot parts or sparks from ignition. Never use gasoline as a cleaning agent.
WARNING
Rotating Parts can cause severe injury.
Stay away while engine is in operation.
Keep hands, feet, hair, and clothing away from all moving parts to prevent injury. Never operate engine with covers, shrouds, or guards removed.
WARNING
Carbon Monoxide can cause severe nausea, fainting or death.
Avoid inhaling exhaust fumes. Never run engine indoors or in enclosed spaces.
Engine exhaust gases contain poisonous carbon monoxide. Carbon monoxide is odorless, colorless, and can cause death if inhaled.

WARNING
Accidental Starts can cause severe injury or death.
Disconnect and ground spark plug lead(s) before servicing.
Before working on engine or equipment, disable engine as follows: 1) Disconnect spark plug lead(s). 2) Disconnect negative (­) battery cable from battery.
WARNING
Hot Parts can cause severe burns.
Do not touch engine while operating or just after stopping.
Never operate engine with heat shields or guards removed.
WARNING
Cleaning Solvents can cause severe injury or death.
Use only in well ventilated areas away from ignition sources.
Carburetor cleaners and solvents are extremely flammable. Follow cleaner manufacturer’s warnings and instructions on its proper and safe use. Never use gasoline as a cleaning agent.

CAUTION
Electrical Shock can cause injury. Do not touch wires while engine is running.
CAUTION
Damaging Crankshaft and Flywheel can cause personal injury.
Using improper procedures can lead to broken fragments. Broken fragments could be thrown from engine. Always observe and use precautions and procedures when installing flywheel.
CAUTION
Failure to utilize or reassemble debris screen as designed could result in debris screen failure and serious personal injury.
WARNING
Uncoiling Spring can cause severe injury. Wear safety goggles or face protection when servicing retractable starter.
Retractable starters contain a powerful, recoil spring that is under tension. Always wear safety goggles when servicing retractable starters and carefully follow instructions in Retractable Starter for relieving spring tension.

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Maintenance

MAINTENANCE INSTRUCTIONS

WARNING
Accidental Starts can cause severe injury or death.
Disconnect and ground spark plug lead(s) before servicing.

Before working on engine or equipment, disable engine as follows: 1) Disconnect spark plug lead(s). 2) Disconnect negative (­) battery cable from battery.

Normal maintenance, replacement or repair of emission control devices and systems may be performed by any repair establishment or individual; however, warranty repairs must be performed by a Kohler authorized dealer.

MAINTENANCE SCHEDULE Weekly Check heavy-duty air cleaner element.

Air Cleaner/Intake

Every 25 Hours or Annually¹ Service/replace low-profile precleaner.

Air Cleaner/Intake

Every 100 Hours or Annually¹
Replace low-profile air cleaner element. Change oil. Remove cooling shrouds and clean cooling areas. Check oil cooler fins, clean as necessary (if equipped).

Air Cleaner/Intake Lubrication System/Clutch
Air Cleaner/Intake Lubrication System

Every 200 Hours Change oil filter. Replace fuel filter.

Lubrication System

Every 250 Hours¹ Replace heavy-duty air cleaner element and check inner element.

Air Cleaner/Intake

Every 300 Hours³ Change oil and filter (KOHLER PRO 10W-50 oil and KOHLER PRO filter only).

Lubrication System

Every 500 Hours¹ Replace heavy-duty inner air cleaner element. Replace spark plugs and set gap.

Air Cleaner/Intake Electrical System

Every 500 Hours²
Have crankshaft spline lubricated.
¹ Perform these procedures more frequently under severe, dusty, dirty conditions. ² Have a Kohler authorized dealer perform this service. ³ Option only if using KOHLER® PRO oil and PRO filter.

REPAIRS/SERVICE PARTS
Kohler genuine service parts can be purchased from Kohler authorized dealers. To find a local Kohler authorized dealer visit KohlerEngines.com or call 1-800-544-2444 (U.S. and Canada).

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Maintenance

OIL RECOMMENDATIONS

All-season ideal oil for

KKOOHHLLEERR®ePnRgiOne1s0.WIt -i5s0spSeycnitfihceatlilcy

Oil is the formulated

to extend the oil and oil filter change interval to 300

Hours when paired with a KOHLER PRO Extended Life

Oil Filter.

300-Hour oil and oil filter change intervals are exclusive to and only authorized on KOHLER engines that utilize
both the KOHLER PRO 10W-50 Synthetic Oil and
KOHLER PRO Extended Life Oil Filter. Alternative
engine oils and oil filters may be used with KOHLER engines but require 100-Hour oil and 200-Hour oil filter change intervals for proper maintenance. Oil must be
API (American Petroleum Institute) service class SJ or
higher. Select viscosity based on air temperature at time
of operation as shown below.

STORAGE
If engine will be out of service for 2 months or more follow procedure below.
1. Add Kohler PRO Series fuel treatment or equivalent to fuel tank. Run engine 2-3 minutes to get stabilized fuel into fuel system (failures due to untreated fuel are not warrantable).
2. Change oil while engine is still warm from operation (NOT required if using KOHLER PRO 10W-50 full-synthetic oil). Remove spark plug(s) and pour about 1 oz. of engine oil into cylinder(s). Replace spark plug(s) and crank engine slowly to distribute oil.
3. Disconnect negative (-) battery cable.
4. Store engine in a clean, dry place.

Kohler PRO 10W-50

10W-30

5W-30

SAE 30

°F -20

0

20 32 40 50 60

80

100

°C -30

-20

-10

0

10

20

30

40

FUEL RECOMMENDATIONS
WARNING
Explosive Fuel can cause fires and severe burns.
Do not fill fuel tank while engine is hot or running.
Gasoline is extremely flammable and its vapors can explode if ignited. Store gasoline only in approved containers, in well ventilated, unoccupied buildings, away from sparks or flames. Spilled fuel could ignite if it comes in contact with hot parts or sparks from ignition. Never use gasoline as a cleaning agent.
NOTE: E15, E20 and E85 are NOT approved and should NOT be used; effects of old, stale or contaminated fuel are not warrantable.
Fuel must meet these requirements:
Clean, fresh, unleaded gasoline. Octane rating of 87 (R+M)/2 or higher. Research Octane Number (RON) 90 octane minimum. Gasoline up to 10% ethyl alcohol, 90% unleaded is
acceptable. Methyl Tertiary Butyl Ether (MTBE) and unleaded
gasoline blend (max 15% MTBE by volume) are approved. Do not add oil to gasoline. Do not overfill fuel tank. Do not use gasoline older than 30 days.

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Engine Dimensions with Low-Profile Air Cleaner

Specifications
Dimensions in millimeters. Inch equivalents shown in [ ].

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Specifications
Engine Dimensions with Heavy-Duty Air Cleaner

135.00 [5.315] AIR FILTER RAIN CAP REMOVAL

424.61 [16.717] 93.33 [3.674]

304.48 [11.987]

272.17 [10.715]

130.00 [5.118] AIR FILTER COVER ASSEMBLY REMOVAL

Dimensions in millimeters. Inch equivalents shown in [ ].

285.90 [11.256]

50.85 [2.002]

OIL FILL LOCATION
PULSE FUEL PUMP

414.17

[16.306]

SAFETY AIR FILTER

ELEMENT REMOVAL

526.49

[20.728]

PRIMARY AIR FILTER

ELEMENT REMOVAL

15.58

30°

[.613]

SPARK PLUG

LIFT STRAP 30°

CRANKSHAFT

15.70 [.618] OIL FILTER REMOVAL

124.34 [4.895] MOUNTING HOLE “A”

SOLENOID SHIFT STARTER

92.10 [3.626]

ENGINE
184.20 [7.252]

CRANKSHAFT

301.36 [11.864]

3/8-16 UNC 2B (INCH) 17.0 [.669] Ø 165.1 [6.50]B.C.
7/16-14 UNC 2B (INCH) 21.0 [.827] Ø 196.85 [7.75]B.C.
ENGINE MOUNTING SURFACE

42.26 [1.664]

115.74 [4.557]

514.05 [20.238]

LIFT STRAP

OIL DIPSTICK

626.92 [24.682]

440.88 [17.357]

1/4 IN. SQ KEYWAY
Ø 25.56 [1.125] 7/16-20 UNF 2B (INCH) 38.10 (1.500)

155.58 [6.125]

70.52 [2.776]

2X OIL DRAIN PLUG 3/8 NPT (INCH)

89.00 [3.504]

MOUNTING HOLE “A”

100.00 [3.937]

89.00 [3.504]

ENGINE MOUNTING SURFACE

54.00 [2.126]

1/4 IN. SQ KEYWAY

3/8-16 UNC 2B 19.05 [.750]

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Specifications

ENGINE IDENTIFICATION NUMBERS Kohler engine identification numbers (model, specification and serial) should be referenced for efficient repair, ordering correct parts, and engine replacement.

Model. . . . . . . . . . . . . . . . . . . . . CH620 Command Engine Horizontal Shaft
Numerical Designation

Specification . . . . . . . . . . . . . . . CH620-0001

Serial . . . . . . . . . . . . . . . . . . . . . 4923500328

Year Manufactured Code

Code Year

49

2019

50

2020

51

2021

Factory Code

GENERAL SPECIFICATIONS4,7
Bore
Stroke
Displacement Oil Capacity (refill) Maximum Angle of Operation (@ full oil level)5

CH18/CH20/ CH22/CH23/

CH22/

CH6208/

CH620/CH621/ CH6408/

CH640/CH641 CH670/CH680

CH25/ CH730/ CH740

CH750

77 mm (3.03 in.)

80 mm (3.15 in.)

83 mm (3.27 in.)

67 mm (2.64 in.)

69 mm (2.7 in.)

624 cc (38 cu. in.)

674 cc (41 cu. in.)

725 cc

747 cc

(44 cu. in.) (46 cu. in.)

1.6-1.8 L (1.7-1.9 U.S. qt.)

25°

TORQUE SPECIFICATIONS4,6

CH18/CH20/ CH22/CH23/

CH22/

CH6208/

CH620/CH621/ CH6408/

CH640/CH641 CH670/CH680

CH25/ CH730/ CH740

CH750

Auto Choke
eChSokteepTMper Motor Lever Set Screw Stepper Motor Bracket Assembly to Carburetor Screws

0.4 N·m (3.5 in. lb.) 4.0 N·m (35 in. lb.)

Blower Housing and Sheet Metal M5 Fasteners
M6 Fasteners

6.2 N·m (55 in. lb.) into new holes 4.0 N·m (35 in. lb.) into used holes
10.7 N·m (95 in. lb.) into new holes 7.3 N·m (65 in. lb.) into used holes

Carburetor and Intake Manifold

Intake Manifold Mounting Fastener (torque in 2 increments)

first to 7.4 N·m (66 in. lb.) finally to 9.9 N·m (88 in. lb.)

M6 Mounting Screw

6.2-7.3 N·m (55-65 in. lb.)

Adapter (for Heavy-Duty Air Cleaner) Mounting Fastener

7.3 N·m (65 in. lb.)

4 Values are in Metric units. Values in parentheses are English equivalents.

5 Exceeding maximum angle of operation may cause engine damage from insufficient lubrication.

6 Lubricate threads with engine oil prior to assembly.

7 Any and all horsepower (hp) references by Kohler are Certified Power Ratings and per SAE J1940 & J1995 hp standards. Details on Certified Power Ratings can be found at KohlerEngines.com.

8 CH620/CH640 engines changed from 624cc to 674cc; displacement can be confirmed on engine nameplate.

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Specifications
TORQUE SPECIFICATIONS4,6
Closure Plate Fastener
Connecting Rod Cap Fastener (torque in increments)
8 mm straight shank 8 mm step-down 6 mm straight shank
Crankcase Breather Cover Fastener
Oil Drain Plug
Cylinder Head Fastener (torque in 2 increments)
Nut
Bolt (torque in 2 increments)
Rocker Arm Screw Black Screw (M6x1.0x34) Silver Screw (M6x1.0x45)
Flywheel Fan Fastener Flywheel Retaining Screw
Fuel Pump-Pulse Fastener
Governor Lever Nut
Ignition Spark Plug Module Fastener Rectifier-Regulator Fastener
Muffler Retaining Nut
Oil Cooler Adapter Nipple
Oil SentryTM Pressure Switch

CH18/CH20/ CH22/CH23/

CH22/

CH6208/

CH620/CH621/ CH6408/

CH640/CH641 CH670/CH680

CH25/ CH730/ CH740

24.4 N·m (216 in. lb.)

CH750

22.7 N·m (200 in. lb.) 14.7 N·m (130 in. lb.) 11.3 N·m (100 in. lb.)
11.3 N·m (100 in. lb.) into new holes 7.3 N·m (65 in. lb.) into used holes
13.6 N·m (10 ft. lb.)

first to 16.9 N·m (150 in. lb.) finally to 35.5 N·m (315 in. lb.) first to 22.6 N·m (200 in. lb.) finally to 41.8 N·m (370 in. lb.)
18.1 N·m (160 in. lb.) 13.6 N·m (120 in. lb.)
9.9 N·m (88 in. lb.) 66.4 N·m (49 ft. lb.)
2.3 N·m (20 in. lb.)
6.8 N·m (60 in. lb.)
27 N·m (20 ft. lb.) 4.0-6.2 N·m (35-55 in. lb.)
1.4 N·m (12.6 in. lb.)
24.4 N·m (216 in. lb.)
27 N·m (20 ft. lb.)
4.5 N·m (40 in. lb.)

4 Values are in Metric units. Values in parentheses are English equivalents. 6 Lubricate threads with engine oil prior to assembly. 8 CH620/CH640 engines changed from 624cc to 674cc; displacement can be confirmed on engine nameplate.

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TORQUE SPECIFICATIONS4,6
Solenoid (Starter) Mounting Hardware
Nippondenso Starter Delco-Remy Starter Nut, Positive (+) Brush Lead Nippondenso Starter Delco-Remy Starter
Speed Control Bracket Fastener
Starter Assembly Thru Bolt
Inertia Drive Nippondenso Solenoid Shift Delco-Remy Solenoid Shift Mounting Screw Brush Holder Mounting Screw
Stator Mounting Screw
Valve Cover Gasket Style Cover Fastener Black O-Ring Style Cover Fastener
w/Shoulder Screws w/Flange Screws and Spacers Yellow or Brown O-Ring Style Cover Fastener w/Integral Metal Spacers
CLEARANCE SPECIFICATIONS4
Camshaft End Play (w/shim) Running Clearance Bore I.D.
New Max. Wear Limit Bearing Surface O.D. New Max. Wear Limit

Specifications

CH18/CH20/ CH22/CH23/

CH22/

CH6208/

CH620/CH621/ CH6408/

CH640/CH641 CH670/CH680

CH25/ CH730/ CH740

CH750

6.0-9.0 N·m (53-79 in. lb.) 4.0-6.0 N·m (35-53 in. lb.)
8.0-12.0 N·m (71-106 in. lb.) 8.0-11.0 N·m (71-97 in. lb.)
10.7 N·m (95 in. lb.) into new holes 7.3 N·m (65 in. lb.) into used holes

4.5-5.7 N·m (40-50 in. lb.) 4.5-7.5 N·m (40-84 in. lb.) 5.6-9.0 N·m (49-79 in. lb.)
15.3 N·m (135 in. lb.)
2.5-3.3 N·m (22-29 in. lb.)

6.2 N·m (55 in. lb.)

3.4 N·m (30 in. lb.)

5.6 N·m (50 in. lb.) 9.9 N·m (88 in. lb.)

9.0 N·m (80 in. lb.)

CH18/CH20/ CH22/CH23/

CH22/

CH6208/

CH620/CH621/ CH6408/

CH640/CH641 CH670/CH680

CH25/ CH730/ CH740

CH750

0.076/0.127 mm (0.0030/0.0050 in.) 0.025/0.063 mm (0.0010/0.0025 in.)
20.000/20.025 mm (0.7874/0.7884 in.) 20.038 mm (0.7889 in.)
19.962/19.975 mm (0.7859/0.7864 in.) 19.959 mm (0.7858 in.)

4 Values are in Metric units. Values in parentheses are English equivalents. 6 Lubricate threads with engine oil prior to assembly. 8 CH620/CH640 engines changed from 624cc to 674cc; displacement can be confirmed on engine nameplate.

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Specifications

CLEARANCE SPECIFICATIONS4
Connecting Rod
Connecting Rod-to-Crankpin Running Clearance New Max. Wear Limit
Connecting Rod-to-Crankpin Side Clearance
Connecting Rod-to-Piston Pin Running Clearance
Piston Pin End I.D. New Max. Wear Limit
Crankcase
Governor Cross Shaft Bore I.D. 6 mm Shaft New Max. Wear Limit 8 mm Shaft New Max. Wear Limit
Crankshaft
End Play (free)
End Play (w/thrust bearing components)
Except CH25 Engines Below Serial No. 2403500008
Bore (in crankcase) New Max. Wear Limit
Crankshaft to Sleeve Bearing (crankcase) Running Clearance-New
Bore (in closure plate) New
Crankshaft Bore (in closure plate)-to-Crankshaft Running Clearance-New
Flywheel End Main Bearing Journal O.D. – New O.D. – Max. Wear Limit Max. Taper Max. Out-of-Round
Closure Plate End Main Bearing Journal O.D. – New O.D. – Max. Wear Limit Max. Taper Max. Out-of-Round
Connecting Rod Journal O.D. – New O.D. – Max. Wear Limit Max. Taper Max. Out- of-Round
T.I.R. PTO End, Crank in Engine Entire Crank, in V-Blocks

CH18/CH20/ CH22/CH23/

CH22/

CH6208/

CH620/CH621/ CH6408/

CH640/CH641 CH670/CH680

CH25/ CH730/ CH740

CH750

0.030/0.055 mm (0.0012/0.0022 in.) 0.070 mm (0.0028 in.)
0.26/0.63 mm (0.0102/0.0248 in.) 0.015/0.028 mm (0.0006/0.0011 in.)
17.015/17.023 mm (0.6699/0.6702 in.) 17.036 mm (0.6707 in.)

6.025/6.050 mm (0.2372/0.2382 in.) 6.063 mm (0.2387 in.)
8.025/8.075 mm (0.3159/0.3179 in.) 8.088 mm (0.3184 in.)
0.070/0.590 mm (0.0028/0.0230 in.) 0.070/1.190 mm (0.0028/0.0468 in.) 0.050/0.750 mm (0.0020/0.0295 in.)
40.965/41.003 mm (1.6128/1.6143 in.) 41.016 mm (1.6148 in.)
0.03/0.09 mm (0.0012/0.0035 in.)
40.987/40.974 mm (1.6136/1.6131 in.)
0.039/0.074 mm (0.0015/0.0029 in.)
40.913/40.935 mm (1.6107/1.6116 in.) 40.84 mm (1.608 in.) 0.022 mm (0.0009 in.) 0.025 mm (0.0010 in.)
40.913/40.935 mm (1.6107/1.6116 in.) 40.84 mm (1.608 in.) 0.022 mm (0.0009 in.) 0.025 mm (0.0010 in.)
35.955/35.973 mm (1.4156/1.4163 in.) 35.94 mm (1.415 in.) 0.018 mm (0.0007 in.) 0.025 mm (0.0010 in.)
0.279 mm (0.0110 in.) 0.10 mm (0.0039 in.)

4 Values are in Metric units. Values in parentheses are English equivalents. 8 CH620/CH640 engines changed from 624cc to 674cc; displacement can be confirmed on engine nameplate.

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Specifications

CLEARANCE SPECIFICATIONS4
Cylinder Bore Bore I.D.
New
Max. Wear Limit
Max. Out-of-Round Max. Taper
Cylinder Head Max. Out-of-Flatness
Governor Governor Cross Shaft-to-Crankcase Running Clearance
6 mm Shaft 8 mm Shaft Cross Shaft O.D. 6 mm Shaft
New Max. Wear Limit 8 mm Shaft New Max. Wear Limit Governor Gear Shaft-to- Governor Gear Running Clearance Gear Shaft O.D. New Max. Wear Limit
Ignition Spark Plug Gap Module Air Gap
Piston, Piston Rings, and Piston Pin
Piston Style A Piston-to-Piston Pin Running Clearance Pin Bore I.D.
New Max. Wear Limit Pin O.D. New Max. Wear Limit Top Compression Ring-to- Groove Side Clearance

CH18/CH20/ CH22/CH23/

CH22/

CH6208/

CH620/CH621/ CH6408/

CH640/CH641 CH670/CH680

CH25/ CH730/ CH740

CH750

77.000/ 77.025 mm
(3.0315/ 3.0325 in.)
77.063 mm (3.0340 in.)

80.000/ 80.025 mm
(3.1496/ 3.1506 in.)

82.988/83.013 mm (3.2672/3.2682 in.)

80.065 mm (3.1522 in.)

83.051 mm (3.2697 in.)

0.12 mm (0.0047 in.)

0.05 mm (0.0020 in.)

0.076 mm (0.003 in.)

0.1 mm (0.004 in.)

0.013/0.075 mm (0.0005/0.0030 in.) 0.025/0.126 mm (0.0009/0.0049 in.)
5.975/6.012 mm (0.2352/0.2367 in.) 5.962 mm (0.2347 in.)
7.949/8.000 mm (0.3129/0.3149 in.) 7.936 mm (0.3124 in.)
0.015/0.140 mm (0.0006/0.0055 in.)
5.990/6.000 mm (0.2358/0.2362 in.) 5.977 mm (0.2353 in.)
0.76 mm (0.030 in.) 0.28/0.33 mm (0.011/0.013 in.)

0.006/0.017 mm (0.0002/0.0007 in.)

17.006/17.012 mm (0.6695/0.6698 in.) 17.025 mm (0.6703 in.)

16.995/17.000 mm (0.6691/0.6693 in.) 16.994 mm (0.6691 in.)

0.040/ 0.080 mm (0.0016/ 0.0031 in.)

0.030/ 0.076 mm (0.0012/ 0.0030 in.)

0.025/0.048 mm (0.0010/0.0019 in.)

4 Values are in Metric units. Values in parentheses are English equivalents. 8 CH620/CH640 engines changed from 624cc to 674cc; displacement can be confirmed on engine nameplate.

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Specifications

CLEARANCE SPECIFICATIONS4

CH18/CH20/ CH22/CH23/

CH22/

CH6208/

CH620/CH621/ CH6408/

CH640/CH641 CH670/CH680

CH25/ CH730/ CH740

CH750

Piston, Piston Rings, and Piston Pin (Style A continued) Middle Compression Ring-to-Groove Side Clearance
Oil Control Ring-to-Groove Side Clearance
Top and Middle Compression Ring End Gap New Bore
Used Bore (Max) Thrust Face O.D.9
New
Max. Wear Limit Piston Thrust Face-to-Cylinder Bore9 Running Clearance
New

0.040/ 0.080 mm (0.0016/ 0.0031 in.)
0.060/ 0.202 mm (0.0024/ 0.0080 in.)
0.25/ 0.45 mm (0.0098/ 0.0177 in.)
0.77 mm (0.030 in.)
76.943/ 76.961 mm
(3.0292/ 3.0299 in.)
76.816 mm (3.0242 in.)

0.030/ 0.076 mm (0.0012/ 0.0030 in.)
0.046/ 0.196 mm (0.0018/ 0.0077 in.)
0.18/ 0.46 mm (0.0071/ 0.0181 in.)
0.80 mm (0.0315 in.)
79.943/ 79.961 mm
(3.1473/ 3.1480 in.)
79.816 mm (3.1423 in.)

0.015/0.037 mm (0.0006/0.0015 in.)
0.026/0.176 mm (0.0010/0.0070 in.)
0.25/0.56 mm (0.0100/0.0224 in.)
0.94 mm (0.037 in.)
82.949/82.967 mm (3.2656/3.2664 in.)
82.822 mm (3.2606 in.)

0.039/0.082 mm (0.0015/0.0032 in.)

Piston Style B Piston-to-Piston Pin Running Clearance Pin Bore I.D.
New Max. Wear Limit Pin O.D. New Max. Wear Limit Top Compression Ring-to- Groove Side Clearance Middle Compression Ring-to-Groove Side Clearance Oil Control Ring-to-Groove Side Clearance Top Compression Ring End Gap New Bore
Used Bore (Max)

0.006/0.017 mm (0.0002/0.0007 in.)

17.006/17.012 mm (0.6695/0.6698 in.) 17.025 mm (0.6703 in.)

16.995/17.000 mm (0.6691/0.6693 in.) 16.994 mm (0.6691 in.)
0.030/0.070 mm (0.001/0.0026 in.)
0.030/0.070 mm (0.001/0.0026 in.)
0.060/0.190 mm (0.0022/0.0073 in.)

0.100/ 0.279 mm (0.0039/ 0.0110 in.)
0.490 mm (0.0192 in.)

0.189/0.277 mm (0.0074/0.0109 in.)
0.531 mm (0.0209 in.)

4 Values are in Metric units. Values in parentheses are English equivalents. 8 CH620/CH640 engines changed from 624cc to 674cc; displacement can be confirmed on engine nameplate. 9 Measure 6 mm (0.2362 in.) above bottom of piston skirt at right angles to piston pin.

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Specifications

CLEARANCE SPECIFICATIONS4

CH18/CH20/ CH22/CH23/

CH22/

CH6208/

CH620/CH621/ CH6408/

CH640/CH641 CH670/CH680

CH25/ CH730/ CH740

CH750

Piston, Piston Rings, and Piston Pin (Style B continued) Middle Compression Ring End Gap
New Bore
Used Bore (Max)
Thrust Face O.D. New
Max. Wear Limit
Piston Thrust Face-to-Cylinder Bore Running Clearance
New

1.400/ 1.679 mm (0.0551/ 0.0661 in.)
1.941 mm (0.0764 in.)
79.966 mm (3.1483 in.)10
79.821 mm (3.1426 in.)10
0.025/ 0.068 mm (0.0010/ 0.0027 in.)10

1.519/1.797 mm (0.0598/0.0708 in.)
2.051 mm (0.0808 in.)
82.978 mm (3.2668 in.)9 82.833 mm (3.2611 in.)9
0.019/0.062 mm (0.0007/0.0024 in.)9

Valves and Valve Lifters
Hydraulic Valve Lifter to Crankcase Running Clearance
Intake Valve Stem-to-Valve Guide Running Clearance
Exhaust Valve Stem-to-Valve Guide Running Clearance
Intake Valve Guide I.D. New Max. Wear Limit
Exhaust Valve Guide I.D. New Max. Wear Limit
Valve Guide Reamer Size Standard 0.25 mm O.S
Intake Valve Minimum Lift
Exhaust Valve Minimum Lift
Nominal Valve Seat Angle

0.0241/0.0501 mm (0.0009/0.0020 in.) 0.038/0.076 mm (0.0015/0.0030 in.) 0.050/0.088 mm (0.0020/0.0035 in.)
7.038/7.058 mm (0.2771/0.2779 in.) 7.134 mm (0.2809 in.)
7.038/7.058 mm (0.2771/0.2779 in.) 7.159 mm (0.2819 in.)
7.048 mm (0.2775 in.) 7.298 mm (0.2873 in.) 8.07 mm (0.3177 in.) 8.07 mm (0.3177 in.)
45°

4 Values are in Metric units. Values in parentheses are English equivalents. 8 CH620/CH640 engines changed from 624cc to 674cc; displacement can be confirmed on engine nameplate. 9 Measure 6 mm (0.2362 in.) above bottom of piston skirt at right angles to piston pin. 10 Measure 13 mm (0.5118 in.) above bottom of piston skirt at right angles to piston pin.

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Specifications

GENERAL TORQUE VALUES
English Fastener Torque Recommendations for Standard Applications Bolts, Screws, Nuts and Fasteners Assembled Into Cast Iron or Steel

Size

Grade 2

Tightening Torque: N·m (in. lb.) ± 20%

8-32

2.3 (20)

10-24

3.6 (32)

10-32

3.6 (32)

1/4-20

7.9 (70)

1/4-28

9.6 (85)

5/16-18

17.0 (150)

5/16-24

18.7 (165)

3/8-16

29.4 (260)

3/8-24

33.9 (300)

Tightening Torque: N·m (ft. lb.) ± 20%

5/16-24

—

3/8-16

—

3/8-24

—

7/16-14

47.5 (35)

7/16-20

61.0 (45)

1/2-13

67.8 (50)

1/2-20

94.9 (70)

9/16-12

101.7 (75)

9/16-18

135.6 (100)

5/8-11

149.5 (110)

5/8-18

189.8 (140)

3/4-10

199.3 (147)

3/4-16

271.2 (200)

Grade 5
2.8 (25) 4.5 (40) 4.5 (40) 13.0 (115) 15.8 (140) 28.3 (250) 30.5 (270)
— —
— 47.5 (35) 54.2 (40) 74.6 (55) 101.7 (75) 108.5 (80) 142.4 (105) 169.5 (125) 223.7 (165) 244.1 (180) 311.9 (230) 332.2 (245) 440.7 (325)

Grade 8
— — — 18.7 (165) 22.6 (200) 39.6 (350) — — —
40.7 (30) 67.8 (50) 81.4 (60) 108.5 (80) 142.5 (105) 155.9 (115) 223.7 (165) 237.3 (175) 311.9 (230) 352.6 (260) 447.5 (330) 474.6 (350) 637.3 (470)

Grade 2 or 5 Fasteners Into Aluminum
2.3 (20) 3.6 (32)
— 7.9 (70)
— 17.0 (150)
— — —
— — — — — — — — — — — — —

Metric Fastener Torque Recommendations for Standard Applications Property Class

Size

4.8

5.8

8.8

10.9

Tightening Torque: N·m (in. lb.) ± 10%

M4

1.2 (11)

1.7 (15)

M5

2.5 (22)

3.2 (28)

M6

4.3 (38)

5.7 (50)

M8

10.5 (93)

13.6 (120)

2.9 (26) 5.8 (51) 9.9 (88) 24.4 (216)

4.1 (36) 8.1 (72) 14.0 (124) 33.9 (300)

Tightening Torque: N·m (ft. lb.) ± 10%

M10

21.7 (16)

27.1 (20)

M12

36.6 (27)

47.5 (35)

M14

58.3 (43)

76.4 (56)

47.5 (35) 82.7 (61) 131.5 (97)

66.4 (49) 116.6 (86) 184.4 (136)

12.9
5.0 (44) 9.7 (86) 16.5 (146) 40.7 (360)

Noncritical Fasteners Into Aluminum
2.0 (18) 4.0 (35) 6.8 (60) 17.0 (150)

81.4 (60) 139.7 (103) 219.7 (162)

33.9 (25) 61.0 (45) 94.9 (70)

Torque Conversions N·m = in. lb. x 0.113 in. lb. = N·m x 8.85 N·m = ft. lb. x 1.356 ft. lb. = N·m x 0.737

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Tools and Aids

Certain quality tools are designed to help you perform specific disassembly, repair, and reassembly procedures. By using these tools, you can properly service engines easier, faster, and safer! In addition, you’ll increase your service capabilities and customer satisfaction by decreasing engine downtime.
Here is a list of tools and their source.

NOTE: Not all tools listed are required to service this engine. SEPARATE TOOL SUPPLIERS

Kohler Tools Contact your local Kohler source of supply.

SE Tools 415 Howard St. Lapeer, MI 48446 Phone 810-664-2981 Toll Free 800-664-2981 Fax 810-664-8181

Design Technology Inc. 768 Burr Oak Drive Westmont, IL 60559 Phone 630-920-1300 Fax 630-920-0011

TOOLS

Description

Alcohol Content Tester For testing alcohol content (%) in reformulated/oxygenated fuels.

Camshaft Endplay Plate For checking camshaft endplay.

Camshaft Seal Protector (Aegis) For protecting seal during camshaft installation.

Dual Gauge Cylinder Leakdown Tester For checking combustion retention and if cylinder, piston, rings, or valves are worn. Individual component available: Adapter 12 mm x 14 mm (Required for leakdown test on XT-6 engines)

Dealer Tool Kit Complete kit of Kohler required tools. Components of 25 761 39-S Ignition System Tester Dual Gauge Cylinder Leakdown Test Tool Oil Pressure Test Kit Digital Vacuum/Pressure Tester

Digital Vacuum/Pressure Tester For checking crankcase vacuum. Individual component available: Rubber Adapter Plug

EFI Service Kit For troubleshooting and setting up an EFI engine. Components of 24 761 01-S Fuel Pressure Tester Noid Light 90° Adapter Code Plug, Red Wire Code Plug, Blue Wire Code Plug, Yellow Wire Can Bus Reset Tool, Green Wire Shrader Valve Adapter Hose Wire Probe Set (2 pieces regular wire with clip; 1 piece fused wire) Hose Removal Tool, Dual Size/End (also sold as individual Kohler tool) K-Line Adapter Jumper Lead Wiring Harness

KFoOrHLLaEptRo®p

Diagnostic or Desktop

System PC.

(KDS)

Gen

2

Components of 25 761 50-S

Engine Communication Module

7 Pin to DB9 Cable

USB Module to PC Cable

7 Pin to 4 Pin Adapter

Mobile KDS (Wireless) Module For mobile Android or iOS EFI diagnostics. Individual component available: Wireless Diagnostic System Interface Cable

Source/Part No. Kohler 25 455 11-S
SE Tools KLR-82405
SE Tools KLR-82417
Kohler 25 761 46-S
Design Technology Inc. DTI-731-03
Kohler 25 761 39-S
Kohler 25 455 01-S Kohler 25 761 46-S Kohler 25 761 06-S Kohler 25 455 22-S Kohler 25 455 22-S
Design Technology Inc. DTI-721-10
Kohler 24 761 01-S
Design Technology Inc. DTI-019 DTI-021 DTI-023 DTI-027 DTI-029 DTI-028 DTI-030 DTI-037 DTI-031 DTI-033
Kohler 25 176 23-S Kohler 25 761 50-S
Kohler 25 761 47-S Kohler 25 761 48-S Kohler 25 761 49-S Kohler 25 761 53-S Kohler 25 761 45-S
Kohler 25 761 44-S

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Tools and Aids

TOOLS
Description
Flywheel Puller For properly removing flywheel from engine.
Flywheel Anchor Bolts, Washers, Nuts Tool Used with Flywheel Puller for properly removing flywheel from 5400 Series engine.
Hose Removal Tool, Dual Size/End (also available in EFI Service Kit) Used to properly remove fuel hose from engine components.
Ignition System Tester For testing output on all systems, including CD.
Inductive Tachometer (Digital) For checking operating speed (RPM) of an engine.
Oil Pressure Test Kit For testing/verifying oil pressure on pressure lubricated engines.
Rectifier-Regulator Tester (120 volt current) Rectifier-Regulator Tester (240 volt current) For testing rectifier-regulators. Components of 25 761 20-S and 25 761 41-S CS-PRO Regulator Test Harness Special Regulator Test Harness with Diode
Spark Advance Module (SAM) Tester For testing SAM (ASAM and DSAM) on engines with SMART-SPARKTM. Starter Servicing Kit (All Starters) For removing and reinstalling drive retaining rings and brushes. Individual component available: Starter Brush Holding Tool (Solenoid Shift)
Stepper Motor Controller Tool For testing operation of stepper motor/Digital Linear Actuator (DLA).
Jumper Lead Tool For use with Stepper Motor Controller Tool to test rotary stepper motor.
Triad/OHC Timing Tool Set For holding cam gears and crankshaft in timed position while installing timing belt.
Valve Guide Reamer (K and M Series) For properly sizing valve guides after installation.
Valve Guide Reamer O.S. (Command Series) For reaming worn valve guides to accept replacement oversize valves. Can be used in low-speed drill press or with handle below for hand reaming.
Reamer Handle For hand reaming using Kohler 25 455 12-S reamer.

Source/Part No. SE Tools KLR-82408
Kohler 25 086 753-S
Kohler 25 455 20-S
Kohler 25 455 01-S
Design Technology Inc. DTI-110
Kohler 25 761 06-S
Kohler 25 761 20-S Kohler 25 761 41-S Design Technology Inc.
DTI-031R DTI-033R Kohler 25 761 40-S
SE Tools KLR-82411
SE Tools KLR-82416 Kohler 25 455 21-S
Kohler 25 518 43-S
Kohler 28 761 01-S
Design Technology Inc. DTI-K828
Kohler 25 455 12-S
Design Technology Inc. DTI-K830

AIDS

Description

Source/Part No.

Camshaft Lubricant (Valspar ZZ613)

Kohler 25 357 14-S

Dielectric Grease (GE/Novaguard G661)

Kohler 25 357 11-S

Dielectric Grease

Loctite® 51360

Kohler Electric Starter Drive Lubricant (Inertia Drive)

Kohler 52 357 01-S

Kohler Electric Starter Drive Lubricant (Solenoid Shift)

Kohler 52 357 02-S

RTV Silicone Sealant

Loctite® 5900® Heavy Body in 4 oz. aerosol dispenser.

Kohler 25 597 07-S

Only oxime-based, oil resistant RTV sealants, such as those listed, are approved

Loctite® 5910®

for use. Permatex® the Right Stuff® 1 Minute GasketTM or Loctite® Nos. 5900® or

Loctite® Ultra Black 598TM

5910® are recommended for best sealing characteristics.

Loctite® Ultra Blue 587TM

When Permatex® Ultra Grey® RTV is to be used, this will be stated in Reassembly Loctite® Ultra Copper 5920TM

section.

Permatex® the Right Stuff® 1

Minute GasketTM

Spline Drive Lubricant

Kohler 25 357 12-S

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FLYWHEEL HOLDING TOOL

Tools and Aids
ROCKER ARM/CRANKSHAFT TOOL

A flywheel holding tool can be made out of an old junk flywheel ring gear and used in place of a strap wrench.
1. Using an abrasive cut-off wheel, cut out a six tooth segment of ring gear as shown.
2. Grind off any burrs or sharp edges.
3. Invert segment and place it between ignition bosses on crankcase so tool teeth engage flywheel ring gear teeth. Bosses will lock tool and flywheel in position for loosening, tightening, or removing with a puller.

A spanner wrench to lift rocker arms or turn crankshaft may be made out of an old junk connecting rod.
1. Find a used connecting rod from a 10 HP or larger engine. Remove and discard rod cap.
2. Remove studs of a Posi-Lock rod or grind off aligning steps of a Command rod, so joint surface is flat.
3. Find a 1 in. long capscrew with correct thread size to match threads in connecting rod.
4. Use a flat washer with correct I.D. to slip on capscrew and approximately 1 in. O.D. Assemble capscrew and washer to joint surface of rod.

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Troubleshooting

TROUBLESHOOTING GUIDE
When troubles occur, be sure to check simple causes which, at first, may seem too obvious to be considered. For example, a starting problem could be caused by an empty fuel tank.
Some general common causes of engine troubles are listed below and vary by engine specification. Use these to locate causing factors.

Engine Cranks But Will Not Start

Battery connected backwards.

Blown fuse.

Carburetor solenoid malfunction.

Choke not closing.

Clogged fuel line or fuel filter.

Diode in wiring harness failed in open circuit mode.

DSAI or DSAM malfunction.

Empty fuel tank.

Faulty electronic control unit.

Faulty ignition coil(s).

Faulty spark plug(s).

Fuel pump malfunction-vacuum hose clogged or

leaking.

Fuel shut-off valve closed.

Ignition module(s) faulty or improperly gapped.

Insufficient voltage to electronic control unit.

Interlock switch is engaged or faulty.

Key switch or kill switch in OFF position.

Low oil level.

Quality of fuel (dirt, water, stale, mixture).

SSMpaArkRTp-luSgPAleRadK(TsM)

malfunction. disconnected.

Engine Starts But Does Not Keep Running

Faulty carburetor. Faulty cylinder head gasket. Faulty or misadjusted choke or throttle controls. Fuel pump malfunction-vacuum hose clogged or
leaking. Intake system leak. Loose wires or connections that intermittently ground
ignition kill circuit. Quality of fuel (dirt, water, stale, mixture). Restricted fuel tank cap vent.

Engine Starts Hard

Clogged fuel line or fuel filter. Engine overheated. Faulty ACR mechanism. Faulty or misadjusted choke or throttle controls. Faulty spark plug(s). Flywheel key sheared. Fuel pump malfunction-vacuum hose clogged or
leaking. Interlock switch is engaged or faulty. Loose wires or connections that intermittently ground
ignition kill circuit. Low compression. Quality of fuel (dirt, water, stale, mixture). Weak spark.

Engine Will Not Crank
Battery is discharged. Faulty electric starter or solenoid. Faulty key switch or ignition switch. Interlock switch is engaged or faulty. Loose wires or connections that intermittently ground
ignition kill circuit. Pawls not engaging in drive cup. Seized internal engine components.
Engine Runs But Misses
Carburetor adjusted incorrectly. Engine overheated. Faulty spark plug(s). Ignition module(s) faulty or improperly gapped. Incorrect crankshaft position sensor air gap. Interlock switch is engaged or faulty. Loose wires or connections that intermittently ground
ignition kill circuit. Quality of fuel (dirt, water, stale, mixture). Spark plug lead(s) disconnected. Spark plug lead boot loose on plug. Spark plug lead loose.
Engine Will Not Idle
Engine overheated. Faulty spark plug(s). Idle fuel adjusting needle(s) improperly set. Idle speed adjusting screw improperly set. Inadequate fuel supply. Low compression. Quality of fuel (dirt, water, stale, mixture). Restricted fuel tank cap vent.
Engine Overheats
Cooling fan broken. Excessive engine load. Fan belt failed/off. Faulty carburetor. High crankcase oil level. Lean fuel mixture. Low cooling system fluid level. Low crankcase oil level. Radiator, and/or cooling system components clogged,
restricted, or leaking. Water pump belt failed/broken. Water pump malfunction.
Engine Knocks
Excessive engine load. Hydraulic lifter malfunction. Incorrect oil viscosity/type. Internal wear or damage. Low crankcase oil level. Quality of fuel (dirt, water, stale, mixture).

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Engine Loses Power Dirty air cleaner element. Engine overheated. Excessive engine load. Restricted exhaust. Faulty spark plug(s). High crankcase oil level. Incorrect governor setting. Low battery. Low compression. Low crankcase oil level. Quality of fuel (dirt, water, stale, mixture). Engine Uses Excessive Amount of Oil Loose or improperly torqued fasteners. Blown head gasket/overheated. Breather reed broken. Clogged, broken, or inoperative crankcase breather. Crankcase overfilled. Incorrect oil viscosity/type. Worn cylinder bore. Worn or broken piston rings. Worn valve stems/valve guides. Oil Leaks from Oil Seals, Gaskets Breather reed broken. Clogged, broken, or inoperative crankcase breather. Loose or improperly torqued fasteners. Piston blow by, or leaky valves. Restricted exhaust.

Troubleshooting
EXTERNAL ENGINE INSPECTION
NOTE: It is good practice to drain oil at a location away from workbench. Be sure to allow ample time for complete drainage.
Before cleaning or disassembling engine, make a thorough inspection of its external appearance and condition. This inspection can give clues to what might be found inside engines (and cause) when it is disassembled.
Check for buildup of dirt and debris on crankcase, cooling fins, grass screen, and other external surfaces. Dirt or debris on these areas can cause overheating.
Check for obvious fuel and oil leaks, and damaged components. Excessive oil leakage can indicate a clogged or inoperative breather, worn or damaged seals or gaskets, or loose fasteners.
Check air cleaner cover and base for damage or indications of improper fit and seal.
Check air cleaner element. Look for holes, tears, cracked or damaged sealing surfaces, or other damage that could allow unfiltered air into engine. A dirty or clogged element could indicate insufficient or improper maintenance.
Check carburetor throat for dirt. Dirt in throat is further indication that air cleaner was not functioning properly.
Check if oil level is within operating range on dipstick. If it is above, sniff for gasoline odor.
Check condition of oil. Drain oil into a container; it should flow freely. Check for metal chips and other foreign particles.
Sludge is a natural by-product of combustion; a small accumulation is normal. Excessive sludge formation could indicate over rich fuel settings, weak ignition, overextended oil change interval or wrong weight or type of oil was used.
CLEANING ENGINE
WARNING
Cleaning Solvents can cause severe injury or death.
Use only in well ventilated areas away from ignition sources.
Carburetor cleaners and solvents are extremely flammable. Follow cleaner manufacturer’s warnings and instructions on its proper and safe use. Never use gasoline as a cleaning agent.
After inspecting external condition of engine, clean engine thoroughly before disassembly. Clean individual components as engine is disassembled. Only clean parts can be accurately inspected and gauged for wear or damage. There are many commercially available cleaners that will quickly remove grease, oil, and grime from engine parts. When such a cleaner is used, follow manufacturer’s instructions and safety precautions carefully.
Make sure all traces of cleaner are removed before engine is reassembled and placed into operation. Even small amounts of these cleaners can quickly break down lubricating properties of engine oil.

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19

Troubleshooting

CRANKCASE VACUUM TEST
WARNING
Carbon Monoxide can cause severe nausea, fainting or death.
Avoid inhaling exhaust fumes. Never run engine indoors or in enclosed spaces.
Engine exhaust gases contain poisonous carbon monoxide. Carbon monoxide is odorless, colorless, and can cause death if inhaled.

WARNING
Rotating Parts can cause severe injury. Stay away while engine is in operation.
Keep hands, feet, hair, and clothing away from all moving parts to prevent injury. Never operate engine with covers, shrouds, or guards removed.

A partial vacuum should be present in crankcase when engine is operating. Pressure in crankcase (normally caused by a clogged or improperly assembled breather) can cause oil to be forced out at oil seals, gaskets, or other available spots.
Crankcase vacuum is best measured with either a water manometer or a vacuum gauge (inches of water gauge only). Complete instructions are provided in kits.

To test crankcase vacuum with manometer:
1. Insert rubber stopper into oil fill hole. Be sure pinch clamp is installed on hose and use tapered adapters to connect hose between stopper and one manometer tube. Leave other tube open to atmosphere. Check that water level in manometer is at 0 line. Make sure pinch clamp is closed.
2. Start engine and run no-load high speed.
3. Open clamp and note water level in tube.
Level in engine side should be a minimum of 10.2 cm (4 in.) above level in open side.
If level in engine side is less than specified (low/no vacuum), or level in engine side is lower than level in open side (pressure), check for conditions in table below.
4. Close pinch clamp before stopping engine.

To test crankcase vacuum with vacuum/pressure gauge (inches of water gauge only):
1. Remove dipstick or oil fill plug/cap.
2. Install adapter into oil fill/dipstick tube opening, upside down over end of a small diameter dipstick tube, or directly into engine if a tube is not used. Insert barbed gauge fitting into hole in stopper.
3. Run engine and observe gauge reading.
Analog tester­needle movement to left of 0 is a vacuum, and movement to right indicates a pressure.
Digital tester­depress test button on top of tester.
Crankcase vacuum should be a minimum of 10.2 cm (4 in.) of water. If reading is below specification, or if pressure is present, check table below for possible causes and conclusions.

Condition

Conclusion

Crankcase breather clogged or inoperative.

NOTE: If breather is integral part of valve cover and cannot be serviced separately, replace valve cover and recheck pressure.

Disassemble breather, clean parts thoroughly, check
sealing surfaces for flatness, reassemble, and recheck pressure.

Seals and/or gaskets leaking. Loose or improperly torque Replace all worn or damaged seals and gaskets. Make

fasteners.

sure all fasteners are tightened securely. Use appropriate

torque valves and sequences when necessary.

Piston blow by or leaky valves (confirm by inspecting components).

Recondition piston, rings, cylinder bore, valves and valves guides.

Restricted exhaust.

Check exhaust screen/spark arrestor (if equipped). Clean or replace as needed. Repair or replace any other damaged/restricted muffler or exhaust system parts.

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Troubleshooting

COMPRESSION TEST
A compression test is best performed on a warm engine. Clean any dirt or debris away from base of spark plug(s) before removing them. Be sure battery is fully charged, choke is off, and throttle is wide open during test. Compression should be at least 160 psi and should not vary more than 15% between cylinders.
Some models (recoil start) may be equipped with an automatic compression release (ACR) mechanism. It is difficult to obtain an accurate compression reading because of ACR mechanism. As an alternative, use cylinder leakdown test described below.
CYLINDER LEAKDOWN TEST
A cylinder leakdown test can be a valuable alternative to a compression test. By pressurizing combustion chamber from an external air source you can determine if valves or rings are leaking, and how badly.

Cylinder leakdown tester is a relatively simple, inexpensive leakdown tester for small engines. This tester includes a quick-connect for attaching adapter hose and a holding tool.
Dual Gauge Test Procedure

1. Run engine until oil temperature reaches and maintains 150°F (66°C) or more for a minimum of 5 minutes. Ideally, engine should be run under normal load conditions.
2. Remove spark plug(s) and air filter from engine.
3. Rotate crankshaft until piston (of cylinder being tested) is at top dead center (TDC) of compression stroke. Hold engine in this position while testing. Holding tool from kit can be used if PTO end of crankshaft is accessible. Lock holding tool onto crankshaft. Install a 3/8 in. breaker bar into hole/slot of holding tool, so it is perpendicular to both holding tool and crankshaft PTO.
If flywheel end is more accessible, use a breaker bar and socket on flywheel nut/screw to hold it in position. An assistant may be needed to hold breaker bar during testing. If engine is mounted in a piece of equipment, it may be possible to hold it by clamping or wedging a driven component. Just be certain engine cannot rotate off TDC in either direction.
4. Connect an air source (at least 100 PSI) to tool.
5. Turn regulator knob clockwise (increase direction). Confirm both gauges read approximately the same air pressure from 0 to 80 PSI. Note any discrepancies between gauges for leakage calculation. Release pressure by turning regulator knob completely counterclockwise before proceeding.

8. Slowly turn regulator knob clockwise until left hand gauge maintains selected test pressure (see chart below).
Left Gauge Regulated Pressure Selection
80 PSI Recommended for engines over 200 cc or those exhibiting high leakage at 35 PSI setting.
35 PSI Recommended for single cylinder walk-behind push mower applications.
9. Compare right gauge reading to Test Pressure Chart on next page to identify percentage of leakage. Also refer to Leakdown Test Results chart on next page for colors, conditions, and action required.
10. For engines exhibiting leakage in yellow or red zone, repeat test procedure. Operate engine under normal load conditions prior to test. Confirm piston is at TDC during test.
NOTE: To prevent damage to gauge assembly, always turn pressure regulator knob to zero (counterclockwise) after each test.

6. Install adapter hose into spark plug hole of cylinder being tested. Use 12 mm x 14 mm adapter if required.
7. Firmly hold engine at TDC. Connect other end of adapter hose to tool quick connect. Turn regulator knob clockwise (increase direction) until left gauge needle reads 20 PSI.

NOTE: When piston is at TDC, little to no holding force should be required when air pressure is applied to cylinder. If excess holding force is required, this indicates piston is not at TDC. Readjust as necessary before proceeding.

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Troubleshooting

Test Pressure Chart for Dual Gauge Tool

Left Gauge Regulated Pressure Selection

Right Gauge Reading in PSI

80 PSI

Recommended for engines over 200 cc or those exhibiting high leakage at

80

72

64

56

48

40

32

24

35 PSI setting.

35 PSI Recommended for single cylinder walk-behind push mower applications.

35 31.5 28 24.5 21 17.5 14 10.5

Percentage of leakage 0% 10% 20% 30% 40% 50% 60% 70%

Green Zone

Yellow Zone

16 8

0

7 3.5 0
80% 90% 100% Red Zone

Test Result Gauge reading in low (green) zone.
Gauge reading in moderate (yellow) zone.
Gauge reading in high (red) zone. Confirm consecutive leakdown test has been performed AFTER engine has been operated under normal load conditions.

Leakdown Test Results

Condition

Action

Piston rings and cylinder in No further action required. good condition.

Air escaping from crankcase Some wear present causing leakage from breather and/or dipstick tube. combustion chamber to crankcase. Repair not
required at this time if breather system is functioning normally.

Air escaping from exhaust.

Exhaust valve leakage present, possibly due to carbon deposits. Repair not required. Carbon cleaning could be performed to reduce leakage.

Air escaping from intake.

Intake valve leakage present, possibly due to carbon deposits. Repair not required. Carbon cleaning could be performed to reduce leakage.

Air escaping from crankcase Excess wear present causing leakage from breather and/or dipstick tube. combustion chamber to crankcase. Breather
system will not function normally and will fail crankcase vacuum test if this condition is truly present. Engine disassembly and analysis required to determine root cause and correction.

Air escaping from exhaust. Air escaping from intake.

Excess exhaust valve leakage present, possibly due to carbon deposits and/or valve to seat sealing issues. Carbon cleaning may reduce leakage. Valve grind and/or component replacement may be necessary. Excess oil consumption and/or excess heat is a suspect cause and must be resolved to prevent reoccurrence.
Excess intake valve leakage present, possibly due to carbon deposits and/or valve to seat sealing issues. Carbon cleaning may reduce leakage. Valve grind and/or component replacement may be necessary. Excess oil consumption through intake valve and/or excess heat is a suspect cause and must be resolved to prevent reoccurrence. Inspect breather system components and intake valve stem sealing.

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24 690 06 Rev. O

Air Cleaner/Intake

AIR CLEANER These systems are CARB/EPA certified and components should not be altered or modified in any way. Low-Profile Air Cleaner Components
A B

C

E

D

F

G

H

A Air Cleaner Cover B

C

Wing Nut

D

E

Rubber Seal

F

G Paper Element H

Air Cleaner Knob Element Cover Precleaner Air Cleaner Base

Heavy-Duty Air Cleaner Components

M I

MJ N

K

L

O

I Air Cleaner Housing J

K

End Cap

L

M

Retaining Clip

N

O

Ejector Area

P

Q

Filter Minder

P Q
Element Dust Ejector Valve
Inner Element Inlet Screen

NOTE: Operating engine with loose or damaged air cleaner components could cause premature wear and failure. Replace all bent or damaged components.
NOTE: Paper element cannot be blown out with compressed air.
Low-Profile
Loosen knob and remove air cleaner cover.
Precleaner 1. Remove precleaner from paper element.
2. Replace or wash precleaner in warm water with detergent. Rinse and allow to air dry.
3. Saturate precleaner with new engine oil; squeeze out excess oil.
4. Reinstall precleaner over paper element.
Paper Element 1. Clean area around element. Remove wing nut,
element cover, and paper element with precleaner.
2. Separate precleaner from element; service precleaner and replace paper element.
3. Check condition of rubber seal and replace if necessary.
4. Install new paper element on base; install precleaner over paper element; reinstall element cover and secure with wing nut.
Reinstall air cleaner cover and secure with knob.
Heavy-Duty
1. Unhook retaining clips and remove end cap(s).
2. Check and clean inlet screen (if equipped).
3. Pull air cleaner element out of housing and replace. Check condition of inner element; replace when dirty.
4. Check all parts for wear, cracks, or damage, and that ejector area is clean.
5. Install new element(s).
6. Reinstall end cap(s) with dust ejector valve/screen down; secure with retaining clips.
BREATHER TUBE
Ensure sure both ends of breather tube are properly connected.
AIR COOLING
WARNING
Hot Parts can cause severe burns.
Do not touch engine while operating or just after stopping.
Never operate engine with heat shields or guards removed.
Proper cooling is essential. To prevent over heating, clean screens, cooling fins, and other external surfaces of engine. Avoid spraying water at wiring harness or any electrical components. Refer to Maintenance Schedule.

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23

Fuel System

Typical carbureted fuel system and related components include:
Fuel tank and valve. Fuel lines. In-line fuel filter. Fuel pump. Carburetor.
Fuel from tank is moved through in-line filter and fuel lines by fuel pump. Fuel then enters carburetor float bowl and is drawn into carburetor body and mixed with air. This fuel-air mixture is then burned in engine combustion chamber.
FUEL RECOMMENDATIONS
Refer to Maintenance.
FUEL LINE
Low permeation fuel line must be installed on carbureted Kohler Co. engines to maintain EPA and CARB regulatory compliance.
FUEL PUMP
These engines use either a mechanical pump or a pulse style fuel pump. Pumping action of pulse style pumps is created by oscillation of positive and negative pressures within crankcase. This pressure is transmitted to pulse pump through rubber hose connected between pump and crankcase. Pumping action causes diaphragm on inside of pump to pull fuel in on its downward stroke and to push it into carburetor on its upward stroke. Two check valves prevent fuel from going backward through pump.
Performance
Minimum fuel delivery rate must be 7.5 L/hr. (2 gal./ hr.) with a pressure at 0.3 psi and a fuel lift of 24 in. A 1.3 L/hr. (0.34 gal./hr.) fuel rate must be maintained at 5 Hz.

Fuel Pump Replacement

Pulse Fuel Pump
NOTE: On most models, pulse line is connected to a
fitting on crankcase, while on early models, it is connected to valve cover.

NOTE: Make sure orientation of new pump is consistent with removed pump. Internal damage may occur if installed incorrectly.

To replace pulse pump follow these steps. Note orientation of pump before removing.

1. Disconnect fuel lines from inlet, outlet, and pulse fittings on fuel pump.

2. Remove screws and take off pump.

3. Connect pulse line to new fuel pump and make sure
opposite end is properly connected to fitting on crankcase or valve cover.

4. Attach new fuel pump using screws. Torque screws to 2.3 N·m (20 in. lb.).

5. Reconnect fuel lines to inlet and outlet fittings and secure with clamps.

Mechanical Pump Mechanical fuel pump is an integral part of valve cover assembly and not serviced separately.

1. Disconnect fuel lines from inlet and outlet fittings. Note orientation.

2. Follow procedure for replacing valve cover. Refer to Disassembly and Reassembly.

3. Reconnect fuel lines to inlet and outlet fittings and secure with clamps.

AUTO CHOKE (if equipped)

ItfroeunbgleinsehoisoetiqnugippproecdewduithreesCshtaorktienTMg,

follow on page

32

of

this

manual.

FUEL SYSTEM TESTS

When engine starts hard or turns over but will not start, fuel system might be causing problems. Test fuel system by performing following test.

1. Check for fuel in combustion chamber.

a. Remove fuel line from inlet fitting of fuel pump.

a. Disconnect and ground spark plug leads. b. Close choke on carburetor. c. Crank engine several times. d. Remove spark plug and check for fuel at tip. 2. Check for fuel flow from tank to fuel pump.

b. Hold line below bottom of tank. Open shut-off valve (if equipped) and observe flow.
3. Check operation of fuel pump. a. Remove fuel line from inlet fitting of carburetor. b. Crank engine several times and observe flow.

Condition Fuel at tip of spark plug. No fuel at tip of spark plug. Fuel flows from fuel line.
No fuel flow from fuel line.
Fuel line condition.

Conclusion
Fuel is reaching combustion chamber.
Check fuel flow from fuel tank (step 2).
Check for faulty fuel pump (step 3).
If fuel pump is working, check for faulty carburetor. Refer to Carburetor.
Check fuel tank cap vent, fuel pickup screen, in-line filter, shut-off valve, and fuel line. Correct any observed problem and reconnect line.
Check for a clogged fuel line. If fuel line is unobstructed, check for overfilled crankcase and/or oil in pulse line. If checks don’t reveal cause of problem, replace pump.

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24 690 06 Rev. O

Fuel System

CARBURETORS

WARNING
Explosive Fuel can cause fires and severe burns.
Do not fill fuel tank while engine is hot or running.

Gasoline is extremely flammable and its vapors can explode if ignited. Store gasoline only in approved
containers, in well ventilated, unoccupied buildings, away
from sparks or flames. Spilled fuel could ignite if it comes in contact with hot parts or sparks from ignition. Never use
gasoline as a cleaning agent.

Keihin Two-Barrel Carburetor Components
D E H F G

B

I

AF C

AB Z
AA AC
AD

AE

A

W V

X

Y

K

U

L

T Q R

M S

J
N
P O

A

Carburetor Body Subassembly

B

Idle Speed Screw

C

Idle Speed Spring

D

F

Retaining Washer

G

Slow JetRight Side

H

Slow JetLeft Side

I

K

O-ring (Fuel Bowl-Upper)

L

O-ring (Fuel Bowl-Lower)

M

Drain Screw

N

P Sealing Washer Q

Float

R

Pin

S

U

Float Valve/ Inlet Needle

V

Main NozzleRight Side

W

Main NozzleLeft Side

X

Z Choke Dust Cap AA Choke Shaft AB

Spring

AC

AE

Choke Plate

AF

Choke Plate Screw

Screw
O-ring (Slow Jet)
Bowl Screw
Screw Main JetRight Side Bushing

E Ground Lead

J

Fuel Bowl

O Fuel Solenoid

T

Float Clip

Y

Main JetLeft Side

AD Choke Lever

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25

Fuel System

Keihin One-Barrel Carburetor Components A
B C

D O
E

F

H

G

I

L K
M NJ

S

W U V
T

A

Carburetor Upper Body (Choke)

B

C

Body Gasket (Formed Rubber)

D

E Inlet Needle Valve F

G

Float Pin

H

I

Carburetor Lower Body (Throttle)

J

K

Idle Fuel Adjusting Needle

L

M Fuel Shut-off Solenoid N

O

Jet (Accelerator Pump Carburetor only)

P

Q

Diaphragm

R

S

O-Ring

T

U

Bushing

V

W Accelerator Pump

Q

R

S

P

Self-relieving Choke
Slow Speed Jet
Clip Float Assembly
Main Jet
Solenoid Seat
Idle Speed Adjusting Screw
Accelerator Pump Cover
Diaphragm Spring Rubber Boot Return Spring

Engines in this series are equipped with Keihin fixed main jet carburetors. CH18-740 engines use a onebarrel carburetor. Most applications use a fuel shut-off solenoid installed in place of fuel bowl retaining screw, and also contain an accelerator pump. All carburetors feature a self-relieving choke. CH750 engines use a Keihin two-barrel carburetor on a matching intake manifold.
Troubleshooting Checklist
When engine starts hard, runs roughly or stalls at low idle speed, check following areas before adjusting or disassembling carburetor.
1. Make sure fuel tank is filled with clean, fresh gasoline.
2. Make sure fuel tank cap vent is not blocked and that it is operating properly.
3. Make sure fuel is reaching carburetor. This includes checking fuel shut- off valve, fuel tank filter screen, in-line fuel filter, fuel lines and fuel pump for restrictions or faulty components as necessary.
4. Make sure air cleaner base and carburetor are securely fastened to engine using gaskets in good condition.
5. Make sure air cleaner element (including precleaner if equipped) is clean and all air cleaner components are fastened securely.
6. Make sure ignition system, governor system, exhaust system, and throttle and choke controls are operating properly.

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Fuel System

Troubleshooting-Carburetor Related Causes

Condition

Possible Cause

Conclusion

Engine starts hard, runs rough, or stalls at idle speed. Engine runs rich (indicated by black, sooty exhaust smoke, misfiring, loss of speed and power, governor hunting, or excessive throttle opening).
Engine runs lean (indicated by misfiring, loss of speed and power, governor hunting, or excessive throttle opening).
Fuel leaks from carburetor.

Low idle fuel mixture (some models)/ Adjust low idle speed tab, then adjust

speed improperly adjusted.

low idle fuel needle.

Clogged air cleaner.

Clean or replace air cleaner.

Choke partially closed during operation.

Check choke lever/linkage to ensure choke is operating properly.

Low idle fuel mixture is improperly adjusted.

Adjust low idle fuel needle (some models).

Float level is set too high.

Adjust float according to Float Replacement Procedure.

Dirt under fuel inlet needle.

Remove needle; clean needle and seat and blow with compressed air.

Bowl vent or air bleeds plugged.

Remove low idle fuel adjusting needle. Clean vent, ports, and air bleeds. Blow out all passages with compressed air.

Leaky, cracked, or damaged float. Submerge float to check for leaks.

Low idle fuel mixture is improperly adjusted.

Adjust low idle fuel needle (some models).

Float level is set too low.

Adjust float according to Float Replacement Procedure.

Idle holes plugged; dirt in fuel delivery Remove low idle fuel adjusting

channels.

needle. Clean main fuel jet and all

passages; blow out with compressed

air.

Float level is set too high.

Adjust float according to Float Replacement Procedure.

Dirt under fuel inlet needle.

Remove needle; clean needle and seat and blow with compressed air.

Bowl vents plugged.

Blow out with compressed air.

Carburetor bowl gasket leaks.

Replace gasket.

Fuel Shut-Off Solenoid
Most carburetors are equipped with a fuel shut-off solenoid. Solenoid is attached to fuel bowl. Solenoid has a springloaded pin that retracts when 12 volts is applied to lead, allowing fuel flow to main jet. When current is removed, pin extends blocking fuel flow.
Below is a simple test, performed with engine off, that can determine if solenoid is functioning properly.
1. Shut off fuel and remove solenoid from carburetor. When solenoid is loosened and removed, gas will leak out of carburetor. Have a container ready to catch fuel.
2. Wipe tip of solenoid with a shop towel or blow with compressed air to remove any remaining fuel. Take solenoid to a location with good ventilation and no fuel vapors present. You will also need a 12 volt power source that can be switched on and off.
3. Be sure power source is switched OFF. Connect positive power source lead to red lead of solenoid. Connect negative power source lead to solenoid body.
4. Turn power source ON and observe pin in center of solenoid. Pin should retract with power ON and return to its original position with power OFF. Test several times to verify operation.

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Fuel System

Carburetor Circuits
Float Fuel level in bowl is maintained by float and fuel inlet needle. Buoyant force of float stops fuel flow when engine is at rest. When fuel is being consumed, float will drop and fuel pressure will push inlet needle away from seat, allowing more fuel to enter bowl. When demand ceases, buoyant force of float will again overcome fuel pressure, rising to predetermined setting and stop flow.
Slow and Mid-Range At low speeds engine operates only on slow circuit. As a metered amount of air is drawn through slow air bleed jets, fuel is drawn through main jet and further metered through slow jet. Air and fuel are mixed in body of slow jet and exit to idle progression (transfer port) chamber. From idle progression chamber, air fuel mixture is metered through idle port passage. At low idle air/fuel mixture is controlled by setting of idle fuel adjusting screws. This mixture is then mixed with main body of air and delivered to engine. As throttle plate opening increases, greater amounts of air/fuel mixture are drawn in through fixed and metered idle progression holes. As throttle plate opens further, vacuum signal becomes great enough at venturi so main circuit begins to work.
Main (high-speed) At high speeds/loads engine operates on main circuit. As a metered amount of air is drawn through air jet, fuel is drawn through main jet. Air and fuel are mixed in main nozzles then enters main body of airflow where further mixing of fuel and air occurs. This mixture is then delivered to combustion chamber. Carburetor has a fixed main circuit; no adjustment is possible.
Carburetor Adjustments
NOTE: Carburetor adjustments should be made only after engine has warmed up.
Carburetor is designed to deliver correct fuel-to-air mixture to engine under all operating conditions. Main fuel jet is calibrated at factory and is not adjustable. Idle fuel adjusting needles are also set at factory and normally do not need adjustment.
Low Idle Speed (RPM) Adjustment NOTE: Actual low idle speed depends on application.
Refer to equipment manufacturer’s recommendations. Low idle speed for basic engines is 1200 RPM.
Place throttle control into idle or slow position. Turn low idle speed adjusting screw in or out to obtain allow idle speed of 1200 RPM (± 75 RPM).
Governed Idle Speed Adjustment (If equipped) 1. Hold governor lever away from carburetor so throttle
lever is against idle speed (RPM) adjustment screw of carburetor. Start engine and allow to warm up, then adjust screw to set approximately 1200 RPM. Check speed using a tachometer. Turn adjustment screw (inner) clockwise (in) to increase or counterclockwise (out) to decrease speed.

2. Release governor lever and check that throttle lever is in idle position. Turn governed idle adjustment screw to obtain equipment manufacturer’s recommended idle speed (1500-1800 RPM). Some engines have a bendable tab that is used to set this speed. A pliers should be used to bend this tab to achieve recommended speed. Governed idle speed (RPM) is typically 300 RPM (approximate) higher than low idle speed.
3. Move throttle lever to wide-open/full throttle position and hold in this position. Turn high speed screw to obtain intended high speed no-load RPM. Governed idle speed must be set before making this adjustment.
Low Idle Fuel Adjustment
Optimum Low Idle Fuel Setting

B C

B C

A

A

D

E

A

Rich

B

C

Midpoint

D

E

Right Side

Lean Left Side

NOTE: Engines will have fixed low idle or limiter caps on idle fuel adjusting needles. Step 2 can only be performed within limits allowed by cap. Do not attempt to remove limiter caps.
1. Place throttle control into idle or slow position. Adjust low idle speed to 1200 RPM. Follow Low Idle Speed (RPM) Adjustment.
2. Low idle fuel needle(s) setting: place throttle into idle or slow position.
a. Turn 1 low idle fuel adjusting needle out (counterclockwise) from preliminary setting until engine speed decreases (rich). Note position of needle. Now turn adjusting needle in (clockwise). Engine speed may increase, then it will decrease as needle is turned in (lean). Note position of needle. Set adjusting needle midway between rich and lean settings.
b. Repeat procedure on other low idle adjustment needle (two-barrel carburetor only).
3. Recheck/adjust Low Idle Speed (RPM) to specified setting.

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Fuel System

High Speed (RPM) Adjustment 1. With engine running, move throttle control to fast.
2. Turn inner adjustment screw outward to decrease, or inward to increase RPM speed. Courage singles require loosening screws on speed control bracket and sliding towards carburetor to lower and away from carburetor to increase speed.
Carburetor Servicing
WARNING
Accidental Starts can cause severe injury or death.
Disconnect and ground spark plug lead(s) before servicing.
Before working on engine or equipment, disable engine as follows: 1) Disconnect spark plug lead(s). 2) Disconnect negative (­) battery cable from battery.
NOTE: Main and slow jets are fixed and size specific and can be removed if required. Fixed jets for high altitudes are available.
Inspect carburetor body for cracks, holes, and other wear or damage.
Inspect float for cracks, holes, and missing or damaged float tabs. Check float hinge and shaft for wear or damage.
Inspect fuel inlet needle and seat for wear or damage. Inspect spring loaded choke plate to make sure it
moves freely on shaft.
Float Replacement/Overhaul/Choke Repair NOTE: Inlet needle center pin is spring loaded. Make
sure float rests against fuel inlet needle without depressing center pin.
If symptoms described in Troubleshooting-Carburetor Related Causes indicate float level problems, remove carburetor from engine to check and/or replace float. Use a float kit to replace float, pin, float valve, clip, and screw.
1. Perform removal procedures for appropriate air cleaner and carburetor outlined in Disassembly.
2. Clean exterior surfaces of dirt or foreign material before disassembling carburetor. Remove bowl retaining screws, or solenoid assembly on most single cylinder engines, and carefully separate fuel bowl from carburetor. Do not damage fuel bowl O-rings. Transfer any remaining fuel into an approved container. Save all parts. Fuel can also be drained prior to bowl removal by loosening/removing bowl drain screw.

3. For two-barrel carburetor, remove float pin screw, float, pin, and inlet needle. Seat for inlet needle is not serviceable and should not be removed.
For one-barrel carburetor, remove float pin, float, and inlet needle. Seat for inlet needle is not serviceable and should not be removed.
4. Clean carburetor bowl and inlet seat areas as required. To reassemble fuel bowl go to step 18, otherwise go to step 5.
5. Carefully remove main jet(s) from carburetor. For two-barrel carburetors, note and mark jets by location for proper reassembly. Main jet(s) may be size/side specific. After main jets are removed, on some carburetors, main nozzles can be removed through bottom of main towers. Note orientation/ direction of nozzles.
For two-barrel carburetor, end with 2 raised shoulders should be out/down adjacent to main jets. Save parts for cleaning and reuse.
6. Position of slow jet varies and is removable only on some styles of carburetors. See correct illustration for corresponding style of carburetor showing location. (On two-barrel carburetors, slow jets may be sized to specific side. Mark or tag jets for proper reassembly. Note small O-ring on bottom of each jet.) Save parts for cleaning and reuse unless a jet kit is also being installed. Clean slow jets using compressed air. Do not use wire or carburetor cleaner.
7. Remove idle speed (RPM) adjustment screw and spring from carburetor. Discard parts.
Carburetor is now disassembled for appropriate cleaning and installation of parts in overhaul kit. Further disassembly is not necessary. Throttle shaft assembly, fuel inlet seat, idle fuel adjustment screws with limiter, and carburetor body, are non-serviceable items and should not be removed. Choke shaft assembly is serviceable, however it should not be removed unless a choke repair kit will be installed.
To install choke repair kit go to step 8, otherwise go to step 18.
8. Remove and discard plastic cap from end of choke lever/shaft assembly.
9. Note position of spring legs and choke plate for correct reassembly later. Remove screws attaching choke plate to choke shaft. Pull shaft out of carburetor body and discard removed parts.
10. Use a screw extractor (easy-out) and remove original choke shaft bushing with old choke lever from carburetor housing. Save bushing to use as a driver for installing new bushing. Discard old lever.
11. Clean I.D. of both choke shaft bores as required.

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Fuel System

12. Insert new bushing through new choke lever from outside and start bushing in outer shaft bore. Position choke lever so protruding boss on carburetor housing is between 2 stops formed in choke lever.
13. Turn old bushing upside down and use it as a driver to carefully press or tap new bushing into carburetor body until it bottoms. Check that choke lever pivots freely without restriction or binding.
14. Install new return spring onto new choke shaft, so outboard leg of spring is behind formed stop on end of choke shaft for two-barrel carburetor or between two formed stops on end of choke shaft on onebarrel carburetor.
Make sure it stays in this location during following step.
15. Slide choke shaft and spring into carburetor. Pivot (preload) shaft 3/4 turn counterclockwise with inner leg of spring against formed stop within choke lever as originally assembled. Outer leg of spring must still be in same position as step 14.
16. Place a drop of Loctite® 222MSTM on threads of each new screw. Position and install new choke plate to flat side of choke shaft. Start screws. Larger cutout must be on right. Close choke and check plate alignment within carburetor throat, then tighten screws securely. Do not overtighten.
17. Check for proper operation and free movement of parts. Install new cap.
18. Clean carburetor body, main jets, vent ports, seats, etc., using a good commercially available carburetor solvent. Keep away from plastic or rubber parts if non-compatible. Use clean, dry compressed air to blow out internal channels and ports. Do not use metal tools or wire to clean orifices and jets. Inspect and thoroughly check carburetor for cracks, wear, or damage. Inspect fuel inlet seat for wear or damage. Check spring loaded choke plate to make sure it moves freely on shaft.
19. Install main nozzle(s) into tower(s) of carburetor body. End of main nozzle(s) with 2 raised shoulders (if equipped) should be out/down (adjacent to main jet(s)). Make sure nozzle(s) are completely bottomed. Carefully install main jet(s) into tower(s) of carburetor body on appropriate side, as identified when removal was performed.
20. For two-barrel carburetor, make sure O-ring near bottom of each slow jet is new, or in good condition. Align and insert slow jets into top of carburetor.
For one-barrel carburetor, install slow jet and new plug into end of slow jet tube.

21. Install large flat retaining washer (if equipped) and secure with mounting screw, attaching ground lead if originally secured by screw.
22. Install new idle speed (RPM) adjustment screw and spring onto carburetor. Thread in until 3 or 4 threads are exposed, as an initial adjustment.
23. Attach inlet needle to plastic tang of float with wire clip. Formed 90° lip should point up, with needle valve hanging down.
24. Install float and inlet needle down into seat and carburetor body. Install new pivot pin through float hinge and secure with new retaining screw.
25. Hold carburetor body so float assembly hangs vertically and rests lightly against fuel inlet needle. Inlet needle should be fully seated but center pin of needle (on retainer clip end) should not be depressed. Check float height adjustment.
Be sure to measure from casting surface, not rubber gasket, if still attached.
26. For two-barrel carburetor, correct float height setting is 17 mm (0.669 in.) ± 1.5 mm (0.059 in.), measured from float bottom to body of carburetor. Replace float if height is different than specified. DO NOT attempt to adjust by bending float tab.
Two-Barrel Carburetor Float Detail
A

1

2

B

A

Float

B

Measure From Casting Surface

When proper float height is obtained, carefully reinstall fuel bowl onto carburetor, using new
O-rings. Secure with original screws. Torque screws
to 2.5 N·m (23 in. lb.) ± 0.3 N·m (3 in. lb.).

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24 690 06 Rev. O

Fuel System

For one-barrel carburetor, correct float height setting is 22 mm (0.86 in.), measured from float bottom to body of carburetor. Adjust float height by carefully bending float tab.
One-Barrel Carburetor Float Detail
B

High Altitude Operation
If this engine is operated at an altitude of 4000 ft. (1219 meters) or above, a high altitude carburetor kit is required. To obtain high altitude carburetor kit information or to find a Kohler authorized dealer, visit KohlerEngines.com or call 1-800-544-2444 (U.S. and Canada).
This engine should be operated in its original configuration below 4000 ft. (1219 meters).
Operating this engine with the wrong engine configuration at a given altitude may increase its emissions, decrease fuel efficiency and performance, and result in damage to the engine.

A

A

Float

B

Tab

When proper float height is obtained, carefully reinstall fuel bowl onto carburetor, using new a new
gasket. Secure with original screws. Torque screws
to 1.7 N·m (15 in. lb.).

27. Set idle mixture screws at midpoint of available adjustment as a preliminary setting.

28. Use new mounting gaskets for air cleaner and carburetor. Reinstall carburetor and disassembled components following Reassembly procedures.

29. Reconnect spark plug leads and negative battery cable. Start engine and perform Low Idle Speed (RPM) Adjustment.

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Fuel System

Electronic Choke (eChokeTM)

eTChihsoskyesTMteims aisn

integrated integrated

control system that checks ambient and engine temperatures and monitors engine speed. through wiring to a master ignition/control module. Extended cranking (beyond 10 seconds)

is not necessary, nor will it improve engine starting.

Calculations and unique software routines developed specifically for this Kohler engine operate a carburetor choke lever through an assembly (bracket, linkage) to control a rotary stepper motor. Power and ground are supplied to
master CDI & eChoke module (Cylinder 1) which provides a signal for stepper motor by way of a control harness that is routed over cylinder #1 baffle.

eChoke Components (Includes ignition due to integrated system) Master CDI & eChoke module Rotary stepper motor Stepper motor bracket, lever, linkage, and associated fasteners Wire harness (for power and ground)

eChokeTM Components

D

B

N

F

M

A C

F E
H G
I

L
K J

A

Master CDI & eChoke Module

B

E Rotary Stepper Motor F

I

Bushing

J

M Speed Control Spring N

2 Pin Connector
Rivet
Stepper Motor Linkage
Idle Adjustment Cable

Red/Green Stripe

C

Lead to Starter

D

Solenoid Stud

Carburetor

G

Stepper Motor Bracket

H Stepper Motor Lever

K

Screw

L

Set Screw

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Fuel System

eChokeTM System Standard Checks
C D
A B

Rotary Stepper

A

Motor 4 Pin

B Main Wiring Harness

Connector

C MIL Test Connector D

2 Pin Connector Access (Some
Engines)

NOTE: Remove air cleaner system to access carburetor DanisdaessCehmokbelyTM/Incospmepcotinoennatsn.dRSeefervritcoe and Reassembly procedure.

Use these procedures and guides to troubleshoot this system and its components. Perform a system reset prior to troubleshooting to verify problem still exists. Start with key switch in OFF position, operate through On-OffOn sequence and restart engine.

There are standard checks that should be made initially to help isolate possible problems:

1. Check choke assembly to ensure choke is properly connected. (Link connected to carburetor and stepper motor lever.) Removal of air cleaner cover, element/precleaner, and air cleaner base is required.

2. Make sure link is located and connected properly.

3. Check that choke stepper motor is functioning. (Operate key switch through On-Off-On sequence to inspect for any choke movement.) Rotary stepper motor function can be tested and confirmed using a stepper motor controller tool and jumper lead tool. Refer to Tools and Aids. Testing instructions are included with these tools.

4. Check that constant power line (RED/GREEN stripe) connection is connected directly to starter stud.

5. Check for battery voltage (nonoperating), must be greater than 12.2 VDC open circuit.

(Low battery voltage may prevent proper operation of stepper motor.)

tehCaht owkilel TMalsloywstecmoninseecqtiuoinppoef danwLitEhDanlaMmIpL

connector to show

MnoILrmcaolnenCehctookreiTMs

operation or specific error codes. accessible by removing air cleaner

system. This lead (white/red stripe) with a bullet

connector next to stepper motor 4 pin connector

(refer to A and C shown above) to which an LED

(connected to lead and +12 volt power line) can be

connected to review operation or look for error codes. Once a lamp is connected, operator can attempt to run through a normal start/crank/run/off sequence and monitor blink codes to determine if controller operation is correct.
Both normal operation and error code indication is listed in blink code table that follows (on next page). Note that code changes for each level of operation.
7. With air cleaner system removed, connect an LED test lamp (see Blink Codes for more detail) or use stepper motor controller tool (see Tools and Aids) MIL bullet terminal and attach tool battery jump leads to battery. Refer to instructions in Blink Codes, Operational Tests, and Failure Modes (on this page and next page).
8. If no MIL light activity is seen, using a DVOM, attach black meter lead to battery ground, connect red meter lead to starter stud, battery voltage should be seen (must be above 12.2 VDC as in step 3).
9. Locate and carefully slide 2 pin connector through blower housing air duct and unplug (some engines). If 2 pin connector is not visible through this duct, blower housing must be removed to gain access.

A

B

A

12 Volt Switched Power Red Wire

12 Volt Constant B Power Red/Green
Wire

With key OFF, using red meter lead, probe terminal 2 (red/green wire). Constant power battery voltage should be seen. If no voltage is seen, cycle key switch ON and OFF and repeat test. If no voltage is seen, confirm harness ground connection. If still no power, possible fusible link failure has occurred in harness. Go to step 11 and test for fuse continuity.

10. If voltage is seen in step 9, move red meter lead to terminal 1. Key OFF, no voltage should be seen. With meter lead connected to terminal 1, turn key to ON position. Battery voltage should now be seen.

11. If no power seen in steps 9 and 10, check for continuity through constant power line (possible fusible link failure). Disconnect battery; remove red/ green wire eyelet terminal from starter solenoid stud. Using a DVOM, check for continuity between eyelet terminal and terminal 2 of 2 pin connector. If no continuity is found, wiring harness must be replaced.

Blink Codes
NOTE: Use of any other type of lamp, other than LED, could damage components.

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Fuel System

Table shows both normal operation and failure mode blinks codes. Normal operation blink codes will be displayed when no failure modes are detected during operation. These codes will only appear if there is no captured failure blink code. Failure mode blink codes are specific to integrated sensors associated with master controller/ignition module.
Operational blink sequence only occurs when routine associated to it is completed, until then LED will continue blinking to previously completed routine.
eChoke Diagnostics and Failure Mode Subroutines DELAY=LED OFF 2 seconds ON=LED ON 0.5 second OFF=LED OFF 0.5 second

Operational Tests

Test Step Number

Operation

1

Power Cycle

3A

Choke Adjusting

4A

Normal

5A

Engine Shutdown

6A

Power Saver Mode

Description of Operation
Remove and reconnect ground on battery.

MIL Lamp Status ON

What is happening at eChokeTM
Choke system will cycle to complete open and then complete close.

Engine started, release Key to RUN position.

ON OFF ON OFF ON DELAY

epCoshiotioken.TM moving to open

Choke operation completed.

ON

epCoshiotioken.TM stays in open

Turn Key from RUN to OFF.

ON DELAY

Once engine has come to a stop, choke will fully close.

System will switch to power saver mode after 30 minutes without engine speed reading.

OFF

System goes into power saver mode after 30 minutes of non use or when key switch moved to OFF.

Failure Modes 1B 2B 3B

Failure to Start

Pause at RUN and attempt to CRANK

engine.

Limit cranking time to about 5 seconds.

For first 4 failed crank attempts, choke

ON

will reposition at each attempt. After

four (4) attempts, key OFF and make

one final attempt to start.

Check other components (spark plug,

ignition, carburetor, fuel solenoid).

Temperature Read Failure

ON OFF ON OFF ON OFF ON OFF ON DELAY

Faulty temperature sensor. System will keep choke closed at Key ON and ramp to open within 10 seconds of engine starting if this is root failure. Replace Master controller/ignition.

RPM Read Failure

System defaults to this failure after 30

seconds of being in Key ON and no

ON OFF ON OFF ON OFF ON DELAY

RPM. Choke will open to half position. Error clears if system reads RPM when

engine is cranking.

Replace Master controller/ignition.

NOTE: Rotary stepper motor can be tested individually using the stepper motor controller tool and jumper lead tool. Refer to Tools and Aids.

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Fuel System

Troubleshooting eChokeTM Related Causes Condition

Possible Cause

Engine starts hard, runs rough, or stalls at idle speed.

Choke not closing/moving a. Broken or missing link.

Engine runs rich (indicated by black, sooty exhaust smoke, misfiring, loss of speed and power, governor hunting, or excessive throttle opening).
Engine runs lean (indicated by misfiring, loss of speed and power, governor hunting, or excessive throttle opening).

b. Loss of constant power or switched power.
c. Loss of system ground.
d. Fusible link is open.
e. Stepper motor not functioning.
f. Electronic component in Master ignition/control module is not functioning.
Choke partially closed during operation.
a. Broken or missing link.
b. Loss of constant power or switched power.
c. Loss of system ground.
d. Fusible link is open.
e. Stepper motor not functioning.
f. Electronic component in Master ignition/control module is not functioning.
Key integrated component in Master ignition/control module is not functioning. Incorrect set up of stepper motor/link/ bracket to carburetor.

Conclusion Stepper motor/bracket/link assembly must allow for full travel, make sure link is located properly and connected. Bad wire harness connection, fusible link failure.
Component failure in Master controller/ignition.
Bad Master Controller harness.
Stepper motor/bracket/link assembly must allow for full travel, make sure link is located properly and connected. Bad wire harness connection, fusible link failure.
Component failure in Master controller/ignition.
Bad Master Controller harness.
Bad ignition module on specific cylinder.
Stepper motor/bracket/link assembly must allow for full travel, make sure link is located properly and connected.

Starting an Engine Equipped with eChokeTM 1. This eChokeTM system automatically controls choke plate position for starting. 2. Activate starter switch. Release switch as soon as engine starts.
3. If engine does not start, remove air cleaner system from carburetor.
4. Confirm connection of stepper motor assembly to carburetor. 5. With key switch set to OFF, choke plate should be fully closed.
6. Confirm movement of choke plate: a. Shut off key switch and test for full travel of rotary stepper motor by disconnection and reconnection of negative (ground) contact at battery.
b. If there is still no movement, separate tests to validate battery voltage and power and ground connection to master controller need to be performed.
7. If movement is noted, attempt to crank and start engine. (Do not exceed 10 seconds of cranking.)

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Fuel System
Replace Rotary Stepper Motor
A B
C D

4. Position new rotary stepper motor on bracket with leads down, insert rivet (as shown) and use rivet tool to pull rivet until tight. Install second rivet to secure motor to bracket.
5. Position rotary stepper motor/bracket/rivet assembly on carburetor and reinstall lever on motor. Secure with set screw. Torque set screw to 0.4 N·m (3.5 in. lb.).
6. Install 2 screws to secure motor/bracket/rivet assembly to carburetor. Torque to 4.0 N·m (35 in. lb.).
7. Connect stepper motor connector to wiring harness. sInesctuarllee. ChokeTM lead in retainer clip; close clip to

A

C

A

Rotary Stepper Motor

B

Installed with Leads Down

C

Stepper Motor Bracket

D

Rivet

NOTE: Remove air cleaner system to access carburetor aDnisdaessCehmokbelyTM/Incospmepcotinoennatsn.dRSeefervritcoe and Reassembly procedure.

Open retainer clip securing #1 inner baffle. Disconnect

s4tewpipreeremChootokrecTMolnenaedcttoor

from wiring harness. Remove 2 screws securing

stepper motor bracket to carburetor.

2. Remove set screw securing stepper motor lever to stepper motor. Carefully remove lever, keeping linkage attached.

3. Remove rotatory stepper motor/bracket/rivet assembly.

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Governor System

GOVERNOR These engines are equipped with an electronic governor or a mechanical governor.

ELECTRONIC GOVERNOR
Electronic Governor System
Engines with electronic governor are equipped with either fixed ignition timing (CH20, CH23, CH680, CH730, certain CH740) or electronic spark advance variable ignition timing (certain CH740). Electronic governor components and basic function are similar, but diagnostic and troubleshooting detail differs based on which design GCU is on engine being serviced.
Electronic governor regulates engine speed at varying loads. Typical electronic governor includes:
Digital linear actuator (DLA). Throttle linkage. Linkage spring. Choke linkage. Throttle lever adapter. Governor control unit (GCU).
Components

C

F

A

B

D

E

G

A

DLA Mounting Plate Screws

B

C

Plastic Linkage Retaining Clip

D

E Throttle Linkage F

G

Throttle Lever Adapter

Digital Linear Actuator (DLA)
Linkage Spring
Choke Linkage

Digital Linear Actuator (DLA)

Energizing bi-directional digital linear actuator coils in proper sequence, causes threaded shaft to move out of, or back into rotor, in precise linear increments. When power is removed, actuator shaft remains in position. DLA must initialize (fully extend) to move throttle plate to closed position, and partially open for starting. Correct adjustment of DLA is critical to achieve full range of throttle plate movement. See Adjustment.

Governor control unit (GCU) senses engine speed by pulse voltage inputs from ignition modules. GCU regulates engine speed by variable input voltage from a customer-supplied potentiometer or a single pole, single throw (SPST) switch.

NOTE: Actual speeds depend on application. Refer to equipment manufacturer’s recommendations.

Potentiometer Specifications

Wiper Voltage

Engine Speed (RPM)

0-1

Low Speed Endpoint

1-9

Variable Speed Endpoint

9-16

High Speed Endpoint

SPST Switch Specifications

Switch Position

Engine Speed (RPM)

Open

Low Speed Endpoint

Closed

High Speed Endpoint

DLA Function DLA function can be tested and confirmed using a stepper motor controller tool. Refer to Tools and Aids. Testing instructions are included with this tool.
GCU Safety Features
In event of an engine overspeed condition, GCU may shut down engine by grounding ignition modules.
GCU may shut down engine by grounding ignition when power to GCU is lost.
Throttle Linkage
Throttle linkage spring will fully open throttle plate if linkage becomes detached from DLA. This will create an overspeed condition causing engine to shut down. DLA shaft will have to be manually screwed back into body, and then retracted before reassembling linkage, or replace DLA and follow adjustment procedure.

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Governor System

Adjustment DLA Details
B A

E

G

F

B

C

A

D C

Troubleshooting
Engine Starts But Will Not Continue to Run 1. Check linkage connection between DLA and throttle
plate.
2. Verify throttle plate is opened during start procedure. Engine is unlikely to start if throttle plate is not opened. Normal opening may be a small amount of a few degrees.
3. Test OEM control system for output voltage. Refer to equipment manufacturer’s manual.
4. Check wire harness and connections.
Engine Does Not Run At Expected Speed 1. Check to see that throttle linkage and DLA have full
range of motion having no mechanical interference.
2. Test OEM control system for output voltage. Refer to equipment manufacturer’s manual.

A

DLA

B Mounting Holes

C

Clevis

D

Keyway

E

Clevis Shaft

F

Rubber Boot

G

Keys

DLA must be in fully retracted position during assembly. Full range of throttle plate movement will not be achieved if DLA is partially extended when assembled. Loosen DLA mounting plate screws located on top of actuator plate. With throttle linkage centered in U-Clip or secured with a retaining clip at end of DLA shaft, press and hold clevis shaft into actuator, while sliding DLA bracket assembly back until throttle plate is fully open. Torque mounting plate screws to 2.5 N·m (22 in. lb.).

If clevis shaft becomes over extended or disconnected from actuator, replace DLA or reinstall clevis shaft as follows:

1. Disconnect linkage and remove DLA from bracket.

2. Remove clevis shaft completely out of DLA.

3. Reinstall rubber boot onto DLA if required.

4. Place clevis shaft into actuator. Rotate clevis shaft clockwise 3 full turns, applying slight pressure, until you feel clevis shaft keyway make contact with key in actuator. When clevis is installed properly, flat of clevis will be aligned with two DLA mounting holes.

NOTE: Continuing to rotate clevis shaft after it has made contact with keyway will damage keyway or actuator.

5. Confirm that key and keyway are in alignment, by hand, press clevis shaft into actuator. It will take a reasonable amount of pressure to do this. If shaft will not move inward, do not force it. Remove clevis shaft and repeat previous step.

6. Reinstall DLA into bracket and connect linkage.

GCU Locations

A

B

D

C

A

Panel

B

GCU

C Blower Housing D

GCU

GCU is either secured to a panel on front of engine or to #1 side of blower housing.

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GCU/Harness Diagnostics and Troubleshooting
NOTE: It is important to use proper sized probes to perform these tests. Probes that are incorrect size can damage connector or harness plug.
Ground and Power Tests 1. Switch key to OFF position.
2. Remove GCU and unplug wiring harness.
These two tests check for power and ground supply to GCU. If either test fails, check if harness, electrical connections, or electrical system need repair.
Test 1 Probe Location

Governor System
Ohms Tests 1. Remove GCU and unplug wiring harness. These two tests are for measuring resistance of DLA circuit that sends a signal to GCU. If either test fails, DLA is no good and should be replaced. If both tests are good, DLA is neither shorted or open, it is good. Another component, connection, or input is most likely at fault. Test 1 Probe Location
A

A

A

Probe Location for Ground Test 1.

Test 1: Identify probe location in connector. Using a continuity tester, check for a good ground. If ground is faulty, inspect unit ground, battery ground, connectors, and wiring harness. Clean or fix connections or replace any faulty parts.

If test 1 checks OK, locate probe location in connector, and check using test 2.

Test 2 Probe Location

A

A

Probe Locations for OHMs Test 1.

Test 1: Identify probe locations in connector. Using a digital multi-meter set to lowest scale (0-200 ohms), place probes onto harness making sure of a good connection. Resistance should be between 47.7 and 58.3 ohms.

If test 1 checks OK, locate wire ends in connector and check using test 2.

Test 2 Probe Location

A

A

Probe Location for Voltage Test 2.

Using a 12 volt meter test for voltage.

On engines equipped with a key switch, turn key switch to ON position.

Voltage should be within +/- 1 volt of battery voltage. If voltage is within +/- 1 volt of battery voltage, harness is OK, replace GCU. If not within +/- 1 volt of battery voltage, check connections and replace wiring harness if necessary.

A

Probe Locations for OHMs Test 2.

Test 2: Identify probe locations in connector. Using a digital multi-meter set to lowest scale (0-200 ohms), place probes onto harness making sure of a good connection. Resistance should be between 47.7 and 58.3 ohms.

If either test 1 or 2 fail resistance test, fault could also be caused by a break/cut in wiring harness. Inspect and test for a potential harness issue prior to replacing DLA assembly.

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Governor System
Speed Control Input A

GCU Designs A

A

B

A CD
E

A

Red Wire with Yellow Tracer.

This connection is either a single wire red with yellow tracer or a 6 pin connector body with a red wire with yellow tracer.

CD

F C

D

A First Design GCU B Second Design GCU

C Green LED Light D Yellow LED Light

E

Third Design GCU

F

Fourth (Latest) Design GCU

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Governor System
Several different GCU designs have been used. First design (24 584 40-S and earlier) had a black potting compound, did not have LED lights, and did not store diagnostic trouble codes. See page 42 for troubleshooting detail and a basic electrical diagram for this GCU design. See pages 50-52 for a troubleshooting flow chart.
Second design did not store codes, but had LED lights for diagnosing a running engine using light codes and blink code chart. See pages 43-45 for troubleshooting detail, GCU Blink Codes, and a basic electrical diagram for this GCU design. See pages 50-52 for a troubleshooting flow chart.
Third design stored codes and had LED lights for diagnosing an engine either with key ON or when engine is running. See pages 46-48 for troubleshooting detail, GCU Blink Codes, and a basic electrical diagram for this GCU design. See pages 50-52 for a troubleshooting flow chart.
Fourth (latest) design stores codes, has LED lights in a different location, and must be used with latest harness. Kits are structured in our online parts lookup system. When replacing an earlier design GCU with latest design, ALWAYS install new GCU and new harness to ensure proper function. See pages 46-47 for troubleshooting detail and GCU Blink Codes. See page 49 for a basic electrical diagram for this GCU design. See pages 50-52 for a troubleshooting flow chart.

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Governor System

FIRST DESIGN GCU Troubleshooting Electronic Governor

Failure Condition Possible Causes

Equipment Observations

Target/Selected Speed not Maintained (Overspeed and/or Underspeed) (No hunt or surge)

Loss of GCU power (B+ or Ground). (Potentially Intermittent)

When connection is lost, no DLA movement will be seen. When connection is restored, engine speed will drop to or below idle speed before returning to target speed position.

Target/Selected Speed Not Maintained (Over speed and/or Under speed) (No hunt or surge)
No Start and/or ungoverned speed below 1500 RPM
No response to selected speed input

Speed Signal (Potentially Intermittent)
Throttle fully closed. No throttle movement. Loss of application supplied speed control input signal.

When connection is lost, no DLA movement will be seen. When connection is restored, throttle returns to target speed position.
Engine may not start due to closed throttle. If engine starts, engine speed will be below 1500 RPM.
GCU regulates engine speed by variable input voltage from a customersupplied source. When signal is lost, engine speed will return to idle. When connection is restored, throttle returns to target speed position.

Inspection/Testing
Test GCU power (red/B+) wire for supply voltage and test ground circuit. Inspect all connections and wires for poor connection. Repair and replace as required.
Inspect all connections and wires for poor connection. Repair and replace as required.
Check system power, physical binding, and wiring etc.
Conduct speed input wire (red w/yellow tracer) voltage test. (Refer to test description on page 51 for more information)

FIRST DESIGN GCU Basic Electrical Diagram of Electronic Governor System
B+
GCU

10 Power

Kill Tab (Speed Signal)
Speed Signal 14

8
Device
12 Ground
13
Application Supplied Speed Control Input
Operation Input Voltage: 0-1 Volts at Idle/9+ Volts at High Speed.

DLA Driver 1

Controls

2

6

7

Ignition Module
2B 2A 1A 1B
DLA

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Governor System

SECOND DESIGN GCU Troubleshooting Electronic Governor

Failure Condition Possible Causes

Equipment Observations

Target/Selected Speed not Maintained (Overspeed and/or Underspeed) (No hunt or surge)

Loss of GCU power (B+ or Ground). (Potentially Intermittent)

When connection is lost, no DLA movement will be seen. When connection is restored, engine speed will drop to or below idle speed before returning to target speed position.

Target/Selected Speed Not Maintained (Over speed and/or Under speed) (No hunt or surge)
No Start and/or ungoverned speed below 1500 RPM
No response to selected speed input

Speed Signal (Potentially Intermittent)
Throttle fully closed. No throttle movement. Loss of application supplied speed control input signal.

When connection is lost, no DLA movement will be seen. When connection is restored, throttle returns to target speed position.
Engine may not start due to closed throttle. If engine starts, engine speed will be below 1500 RPM.
GCU regulates engine speed by variable input voltage from a customersupplied source. When signal is lost, engine speed will return to idle. When connection is restored, throttle returns to target speed position.

Inspection/Testing
Test for GCU power by turning key to ON position and inspect for LED lights to illuminate or test GCU power (red/B+) wire for supply voltage and test ground circuit. Inspect all connections and wires for poor connection. Repair and replace as required.
View GCU blink codes for potential trouble code. Inspect all connections and wires for poor connection. Repair and replace as required.
Check system power, physical binding, and wiring etc.
Conduct speed input wire (red w/yellow tracer) voltage test. (Refer to test description on page 51 for more information)

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Governor System

SECOND DESIGN GCU Blink Codes

Failure Condition Possible Causes

Overspeed (Over External noise on ignition input

4500 RPM for 0.5 seconds sustained)

Frozen carb throttle plate

DLA failure

Mechanical bindage

Out of RPM range Frozen carb throttle plate

(Unable to maintain an average RPM of

DLA failure

+/- 100 RPM of

Mechanical bindage

setpoint for 10 seconds)

Bad fuel

Bad ignition system

Missing ignition pulse detected

RFI interference Poor lead connection

Bad ignition module

Ignition module signal missing on startup

Ignition leads disconnected

Watchdog Interrupt RFI interference

Overtemp

Software bug

Lightning

Excessive Battery Voltage (> 18v for 0.5 seconds)

Good condition

Engine is operating normally

Response
Ground to kill, close carb throttle plate

Response Time
0.2 seconds

LED Diagnostics

Yellow LED Green LED

Flashing

On

Normal operation 10 seconds Solid on or Flashing solid off

Normal operation N/A

DLA will remain at N/A start point

Ground to kill,

N/A

close carb throttle

plate

Pulse Off

Solid on or solid off

Off

On

Flashing

Flashing

Ground to kill,

0.5

close carb throttle seconds

plate

Flashing

Normal operation

10 seconds On of good engine run time

Off
Solid on or solid off

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Governor System

SECOND DESIGN GCU Basic Electrical Diagram of Electronic Governor System
B+
GCU

10 Power

Speed Signal 14

Kill Tab (Speed Signal)

8 Device 12 Ground
13

Green LED Light Yellow LED Light

DLA Driver 1

Controls

2

6

7

Ignition Module
2B 2A 1A 1B

Application Supplied Speed Control Input

DLA

Operation Input Voltage: 0-1 Volts at Idle/9+ Volts at High Speed.

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Governor System

THIRD AND FOURTH DESIGN GCU Troubleshooting Electronic Governor

Failure Condition Possible Causes

Equipment Observations

Target/Selected Speed not Maintained (Overspeed and/or Underspeed) (No hunt or surge)

Loss of GCU power (B+ or Ground). (Potentially Intermittent)

When connection is lost, no DLA movement will be seen. When connection is restored, engine speed will drop to or below idle speed before returning to target speed position.

Target/Selected Speed Not Maintained (Over speed and/or Under speed) (No hunt or surge)

Speed Signal (Potentially Intermittent)

When connection is lost, no DLA movement will be seen. When connection is restored, throttle returns to target speed position.

No Start and/or ungoverned speed below 1500 RPM

Throttle fully closed. No throttle movement.

No response to

Loss of application

selected speed input supplied speed

control input signal.

While cranking, GCU commands DLA to open to a predetermined position. If no movement is seen, engine may not start due to closed throttle. If engine starts, engine speed may be below 1500 RPM.
GCU regulates engine speed by variable input voltage from a customersupplied source. When signal is lost, engine speed will return to idle. When connection is restored, throttle returns to target speed position.

Inspection/Testing
Test for GCU power by turning key to ON position and inspect for LED lights to illuminate or test GCU power (red/B+) wire for supply voltage and test ground circuit. Inspect all connections and wires for poor connection. Repair and replace as required.
View GCU blink key ON and running codes for potential trouble code. Inspect all connections and wires for poor connection. Repair and replace as required.
Check system power, physical binding, and wiring etc.
Conduct speed input wire (red w/yellow tracer) voltage test. (Refer to test description on page 51 for more information)

THIRD AND FOURTH DESIGN GCU Blink Codes for Software Stored Codes – Activated when key is turned to ON position.

Failure Condition Possible Causes

Response

Response

LED Diagnostics

Time

Yellow LED Green LED

Speed Error

BLINKS

ON

Watchdog Interrupt RFI interference Overtemp Software bug

Ground to kill, close carb throttle plate

BLINKS

BLINKS

Lightning

Overspeed (Over External noise on ignition input Ground to kill,

1 second ON

ON

4500 RPM for 0.5 seconds sustained)

Frozen carb throttle plate

close carb throttle delay plate

DLA failure

Mechanical bindage

Excessive Battery Open battery voltage on B+

Ground to kill,

0.5

OFF

ON

Voltage

24 V battery (Not Compatible close carb throttle seconds

(> 18v for 0.5

with system, 12 V battery only) plate

seconds)

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Governor System

THIRD AND FOURTH DESIGN GCU Blink Codes for Software Running Codes – Activated when engine is running.

Failure Condition Possible Causes

Response

Response

LED Diagnostics

Time

Yellow LED Green LED

Running Normally

None

BLINKS

BLINKS

RPM Too High

Mechanical bindage

None

ON

BLINKS

RPM Too Low

Mechanical bindage

None

ON

BLINKS

Missing Pulse (Normal RPM)

Faulty igniting Faulty ignition wiring

BLINKS

ON

Missing Pulse (RPM Too High)

Faulty igniting Faulty ignition wiring

ON

ON

Missing Pulse (RPM Too Low)

Faulty igniting Faulty ignition wiring

OFF

ON

Sleep Mode

Left in run mode (key ON) Power at GCU with no ignition pulses

System Shutdown 30 Minutes OFF

OFF

Watchdog Interrupt RFI interference Overtemp Software bug

Ground to kill,

N/A

close carb throttle

plate

BLINKS

OFF

Lightning

Overspeed (Over External noise on ignition input

4500 RPM for 0.5 seconds sustained)

Frozen carb throttle plate

DLA failure

Mechanical bindage

1 second ON delay

OFF

Excessive Battery Voltage (> 18v for 0.5 seconds)

Open battery voltage on B+ 24 V battery (Not Compatible with system, 12 V battery only)

Ground to kill,

0.5

close carb throttle seconds

plate

OFF

OFF

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47

Governor System

THIRD DESIGN GCU Basic Electrical Diagram of Electronic Governor System
B+
GCU

10 Power

Speed Signal 14

Kill Tab (Speed Signal)

8 Device 12 Ground
13

Green LED Light Yellow LED Light

DLA Driver 1

Controls

2

6

7

Ignition Module
2B 2A 1A 1B

Application Supplied Speed Control Input

DLA

Operation Input Voltage: 0-1 Volts at Idle/9+ Volts at High Speed.

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Governor System

FOURTH (LATEST) DESIGN GCU Basic Electrical Diagram of Electronic Governor System
B+
GCU

10 Power

Speed Signal 14

Kill Tab (Speed Signal)

8 Device Ground 13

Green LED Light Yellow LED Light
1
DLA Driver
Controls 2 6 7

Ignition Module
2B 2A 1A 1B

Application Supplied Speed Control Input

DLA

Operation Input Voltage: 0-1 Volts at Idle/9+ Volts at High Speed.

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49

Governor System
Electronic Governor Troubleshooting Flow Chart Turn off key switch.

Do Not Touch Digital Linear Actuator (DLA) NOTE: DLA is not a solenoid. It is a precision electronic motor. Do not exert force to center clevis shaft!

Visually inspect DLA and Linkage. See illustrations on pages 37 and 38.

Fail if

Pass if

Confirm that: 1. Clevis shaft and boot in place. 2. Clip attached. 3. DLA wire attached.

Clevis shaft and boot are out of DLA.

Reinstall using procedure on page 38 (see illustrations on pages 37 and 38) or replace DLA and follow adjustment procedure on page 38.

Start/test run unit for engine speed control operation.

Fail
Pass Go to Speed Input Wire Test on next page.

Test control system of equipment. Refer to Equipment Manufacturer’s diagnostic procedures for control system.

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Electronic Governor Troubleshooting Flow Chart (Continued)

Governor System

Speed Input Wire Test

Locate Speed Control input wire. This connection is either a single wire red with yellow tracer, or a 6 pin connector body with a red wire with yellow tracer. See illustration on page 40.

Unplug single spade terminal and connect a jumper wire to red wire with a yellow tracer on engine wire harness.

or

Probe red with yellow wire

on 6 pin connector.

Start engine in normal manner as described in Owner’s Manual. (Engine will initially operate at speed it was last run or shut down, then will go to idle).

Attach open end of jumper wire to positive (+) battery terminal.

Engine speed increases (if it was at low speed).

Fail

Pass

Engine speed does not change.

Operation Input Voltage: 0-1 Volts at Idle/9+ Volts at High Speed.
Kohler electronic governor system tests OK. Test control system of equipment. Refer to Equipment Manufacturer’s diagnostic procedures for control system.

Refer to GCU Designs on page 40 and identify which design GCU is on engine.

If GCU is first design (no LED lights) proceed directly to ground power test. All other GCU designs see next step.

All other GCU designs: Inspect for LED light illumination when key is in ON position. If lights do not illuminate, proceed to GCU ground power test. If power and ground tests are found to be OK, but no LED light illumination while in key ON position, indications are the GCU has failed. Replace GCU. If LEDs illuminate, use blink codes (refer to pages 44 or 46-47) for GCU design in use.

Proceed to Ground/Power and OHMs test for GCU. Refer to page 39.

24 690 06 Rev. O

Remove GCU and unplug wiring harness. See illustration on page 38.

GCU Circuit Test. Continued on next page

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Governor System
Electronic Governor Troubleshooting Flow Chart (Continued)

Inspect wiring harness for broken wire or bad connections. (Repair/Replace as required).

Test supply ground circuit to GCU using a continuity OHM/tester. Refer to page 39.

Test supply voltage to GCU using volt meter. Refer to page 39 (battery voltage +/- 1 volt) Note: Prevent Damage to Connector. Do Not Use Oversized Probe Tips.

If a Stepper Motor Controller Tool is available (see Tools and Aids), DLA function can be tested and confirmed. Testing instructions are included with tool. If tool is not available, proceed to DLA Circuit Test.

Proceed to DLA Circuit Test.

If test fails, DLA is no good and should be replaced. If DLA test is good, another component, connection, or input is most likely at fault. Replace GCU and harness.

Test 1: Identify wire ends in connector. Using a digital multi-meter set to lowest scale (0-200 ohms) place probes onto harness making sure of a good connection. Resistance should be between 47.7 and 58.3 ohms. Refer to page 39.

Test 2: Identify wire ends in connector. Using a digital multi-meter set to lowest scale (0-200 ohms) place probes onto harness making sure of a good connection. Resistance should be between 47.7 and 58.3 ohms. Refer to page 39.

If either test fails, DLA is no good and should be replaced. If both tests are good, DLA is neither shorted or open, and should be good. Another component, connection, or input is most likely at fault.

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Governor System

MECHANICAL GOVERNOR A centrifugal flyweight mechanical governor is designed to hold engine speed constant under changing load conditions. Governor gear/flyweight mechanism is mounted inside crankcase on closure plate, and is driven off gear on camshaft. Governor Components
J I

D GA

K H Inside Engine

F E
B
C

A

Throttle Lever

B

Throttle Linkage

C

Governor Lever

D

Choke Linkage

E Governor Spring

F Governed Idle Spring G

Control Bracket

H

Regulating Pin

I

Governor Gear

J

Locking Tab Thrust Washer

K Governor Gear Shaft

This governor design works as follows:

Centrifugal force acting on rotating governor gear assembly causes flyweights to move outward as speed increases. Governor spring tension moves them inward as speed decreases.
As flyweights move outward, they cause regulating pin to move outward. Regulating pin contacts tab on cross shaft causing shaft to rotate. One end of cross shaft protrudes through
crankcase. Rotating action of cross shaft is transmitted to throttle lever of carburetor through external linkage. When engine is at rest, and throttle is in FAST position, tension of governor spring holds throttle plate open. When
engine is operating, governor gear assembly is rotating. Force applied by regulating pin against cross shaft tends to
close throttle plate. Governor spring tension and force applied by regulating pin balance each other during
operation, to maintain engine speed. When load is applied and engine speed and governor gear speed decreases, governor spring tension moves
governor lever to open throttle plate wider. This allows more fuel into engine, increasing engine speed. As speed reaches governed setting, governor spring tension and force applied by regulating pin will again offset each other to hold a steady engine speed.

Governor Adjustments

NOTE: Do not tamper with governor setting. Overspeed is hazardous and could cause personal injury.

Initial Adjustment Procedure Make this adjustment whenever governor arm is loosened or removed from cross shaft. Adjust as follows:

1. Make sure throttle linkage is connected to governor arm and throttle lever on carburetor.

2. Loosen nut holding governor lever to cross shaft.

3. Move governor lever toward carburetor as far as it will go (wide open throttle) and hold in this position.

4. Insert a long thin rod or tool into hole on cross shaft and rotate shaft counterclockwise (viewed from end) as far as it will turn, then torque nut to 6.8 N·m (60 in. lb.).

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Governor System
Sensitivity Adjustment Governor sensitivity is adjusted by repositioning governor spring in holes of governor lever. If speed surging occurs with a change in engine load, governor is set too sensitive. If a big drop in speed occurs when normal load is applied, governor should be set for greater sensitivity and adjust as follows: 1. To increase sensitivity, move spring closer to governor cross shaft. 2. To decrease sensitivity, move spring away from governor cross shaft.

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Lubrication System

This engine uses a full pressure lubrication system which delivers oil under pressure to crankshaft, camshaft, connecting rod bearing surfaces, and hydraulic valve lifters. A high-efficiency gerotor oil pump maintains high oil flow and oil pressure, even at low speeds and high operating temperatures. A pressure relief valve limits maximum pressure of system. Closure plate must be removed to service oil pickup, pressure relief valve, and oil pump. Lubrication Components
B C
A
D
H

G E
F

A Press-In Dipstick B Thread-On Dipstick

C

Oil SentryTM

D

Oil Fill Cap

E

Oil Cooler

F

Oil Filter

G

Oil Drain Plug

H

Back Side

OIL RECOMMENDATIONS

Refer to Maintenance.

CHECK OIL LEVEL

NOTE: To prevent extensive engine wear or damage, never run engine with oil level below or above operating range indicator on dipstick.

Ensure engine is cool. Clean oil fill/dipstick areas of any debris.

1. Remove dipstick; wipe oil off.

a. Press-in cap: reinsert dipstick into tube; press completely down.

or

b. Thread-on cap: reinsert dipstick into tube; rest cap on tube, do not thread cap onto tube.

2. Remove dipstick; check oil level. Level should be at top of indicator on dipstick.

3. If oil is low on indicator, add oil up to top of indicator mark.
4. Reinstall dipstick and tighten securely.
CHANGE OIL AND FILTER Change oil while engine is warm.
1. Clean area around oil fill cap/dipstick, drain plug/oil drain valve.
a. Remove drain plug and oil fill cap/dipstick. Allow oil to drain completely.
or
b. Open oil drain valve cap; if needed, attach a length of 1/2 in. I.D. hose to direct oil into appropriate container; twist valve drain body counterclockwise and pull. Remove dipstick. Allow oil to drain completely.
2. Clean area around oil filter. Place a container under filter to catch any oil and remove filter. Wipe off mounting surface.
a. Reinstall drain plug. Torque to 13.6 N·m (10 ft. lb. ).
or
b. Close oil drain valve body, remove hose (if used), and replace cap.
3. Place new filter in shallow pan with open end up. Fill with new oil until oil reaches bottom of threads. Allow 2 minutes for oil to be absorbed by filter material.
4. Apply a thin film of clean oil to rubber gasket on new filter.
5. Refer to instructions on oil filter for proper installation.
6. Fill crankcase with new oil. Level should be at top of indicator on dipstick.
7. Reinstall oil fill cap/dipstick and tighten securely.
8. Start engine; check for oil leaks. Stop engine; correct leaks. Recheck oil level.
9. Dispose of used oil and filter in accordance with local ordinances.
OIL COOLER (if equipped)
Blower Housing Mounted Oil Cooler
1. Clean fins with a brush or compressed air.
2. Remove screws securing oil cooler and tilt to clean back side.
3. Reinstall oil cooler.
Crankcase Mounted Oil Cooler
Clean fins with a brush or compressed air.

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Lubrication System

OIL SENTRYTM (if equipped)

This switch is designed to prevent engine from starting

in a low down a

oil or no oil condition. running engine before

OdailmSaegnetryoTMccmuarsy.

not shut In some

applications this switch may activate a warning signal.

Read your equipment manuals for more information.

hOOoinlleSeeinsngstinreyeaTMslepndroewtseisthquuraeip1sp/we8di- t2cw7hiNtihs.PiOn.Tsil.tFSa.lelepnditpreyinTMpbilnuresgat.athlleartiocnover.

Installation
1. Apply pipe sealant with Teflon® (Loctite® PST® 592TM Thread Sealant or equivalent) to threads of switch.
2. Install switch into tapped hole in breather cover.
3. Torque switch to 4.5 N·m (40 in. lb.).

Testing
Compressed air, a pressure regulator, pressure gauge, and a continuity tester are required to test switch.
1. Connect continuity tester across blade terminal and metal case of switch. With 0 psi pressure applied to switch, tester should indicate continuity (switch closed).
2. Gradually increase pressure to switch. As pressure increases through range of 3-5 psi tester should indicate a change to no continuity (switch open). Switch should remain open as pressure is increased to 90 psi maximum.
3. Gradually decrease pressure through range of 3-5 psi. Tester should indicate a change to continuity (switch closed) down to 0 psi.
4. Replace switch if it does not operate as specified.

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SPARK PLUGS CAUTION
Electrical Shock can cause injury. Do not touch wires while engine is running. Spark Plug Component and Details
A B

Electrical System
Inspection Inspect each spark plug as it is removed from cylinder head. Deposits on tip are an indication of general condition of piston rings, valves, and carburetor. Normal and fouled plugs are shown in following photos: Normal

Plug taken from an engine operating under normal conditions will have light tan or gray colored deposits. If center electrode is not worn, plug can be set to proper gap and reused.
Worn

C

D

A

Wire Gauge

B

C Ground Electrode D

Spark Plug Gap

NOTE: Do not clean spark plug in a machine using abrasive grit. Some grit could remain in spark plug and enter engine causing extensive wear and damage.
Engine misfire or starting problems are often caused by a spark plug that has improper gap or is in poor condition.
Engine is equipped with following spark plugs:

Gap

0.76 mm (0.030 in.)

Thread Size 14 mm

Reach

19.1 mm (3/4 in.)

Hex Size 15.9 mm (5/8 in.)

Refer to Maintenance for Repairs/Service Parts.

Service
Clean out spark plug recess. Remove plug and replace. 1. Check gap using wire feeler gauge. Adjust gap to
0.76 mm (0.030 in.). 2. Install plug into cylinder head. 3. Torque plug to 27 N·m (20 ft. lb.).

On a worn plug, center electrode will be rounded and gap will be greater than specified gap. Replace a worn spark plug immediately. Wet Fouled
A wet plug is caused by excess fuel or oil in combustion chamber. Excess fuel could be caused by a restricted air cleaner, a carburetor problem, or operating engine with too much choke. Oil in combustion chamber is usually caused by a restricted air cleaner, a breather problem, worn piston rings, or valve guides.

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57

Electrical System

Carbon Fouled
Soft, sooty, black deposits indicate incomplete combustion caused by a restricted air cleaner, over rich carburetion, weak ignition, or poor compression. Overheated
Chalky, white deposits indicate very high combustion temperatures. This condition is usually accompanied by excessive gap erosion. Lean carburetor settings, an intake air leak, or incorrect spark timing are normal causes for high combustion temperatures.

BATTERY

A 12-volt battery with 400 cold cranking amps (cca) is generally recommended for starting in all conditions. A smaller capacity battery is often sufficient if an application is started only in warmer temperatures. Refer to following table for minimum capacities based on anticipated ambient temperatures. Actual cold cranking requirement depends on engine size, application, and starting temperatures. Cranking requirements increase as temperatures decrease and battery capacity shrinks. Refer to equipment’s operating instructions for specific battery requirements.

Battery Size Recommendations

Temperature

Battery Required

Above 32°F (0°C)

200 cca minimum

0°F to 32°F (-18°C to 0°C)

250 cca minimum

-5°F to 0°F (-21°C to -18°C) 300 cca minimum

-10°F (-23°C) or below

400 cca minimum

If battery charge is insufficient to turn over engine, recharge battery.

Battery Maintenance
Regular maintenance is necessary to prolong battery life.

Battery Test To test battery, follow manufacturer’s instructions.

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ELECTRONIC IGNITION SYSTEMS Ignition System Components

Electrical System
CDI/MDI Ignition Module Identification

F

E

A

D

B

C

Kill Switch/

A

Off Position of

B

Key Switch

Air Gap

C

Flywheel

D

Magnet

E

Spark Plug

F Ignition Modules

There are 3 different types of ignition systems used on these engines. All systems use an ignition module which energizes spark plug. Difference in systems is in way ignition timing is triggered.
All ignition systems are designed to be trouble free for life of engine. Other than periodically checking/replacing spark plugs, no maintenance or timing adjustments are necessary or possible. Mechanical systems do occasionally fail or break down. Refer to Troubleshooting to determine root of a reported problem.
Reported ignition problems are most often due to poor connections. Before beginning test procedure, check all external wiring. Be certain all ignition- related wires are connected, including spark plug leads. Be certain all terminal connections fit snugly. Make sure ignition switch is in run position.
CDI/MDI Ignition see pages 59-62.
Smart-SparkTM Ignition see pages 63-68.
DSAI Ignition see pages 69-71.

A

B

A CDI Ignition Module B MDI Ignition Module
These systems use a capacitive discharge (CD) coil. With CDI fixed timing, ignition timing and spark remains constant regardless of engine speed. Timing of spark is controlled by location of flywheel magnet group as referenced to engine TDC. MDI adjustable timing uses a digital microprocessor which is located in ignition modules. Ignition timing varies depending upon engine speed with this system.
A typical CDI/MDI ignition system consists of:
1 magnet assembly which is permanently affixed to flywheel.
2 electronic capacitive-discharge (CDI) or magnetic discharge (MDI) ignition modules which mount on engine crankcase.
1 kill switch (or key switch) which grounds modules to stop engine.
2 spark plugs.

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Electrical System
Wiring Diagram-15/20/25 Amp Regulated Battery Charging System with CDI/MDI

A

E F

B

D

F

A

C

G H

AA

AB

Z

AC V

W U
I

Y

B

K

LJ

R V T
S R
Q

X W

AH AF

AG AD
AO

AJ AI

O

P

AH R

AK AE

AL

V

T

N

M

AN

AM V R

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Electrical System

A

Spark Plug(s)

B Oil Pressure Switch C Oil SentryTM (Green) D

White Kill

E

Flywheel Stator Assembly

F

Ignition Module

G

CDI/MDI Ignition

H

Rectifier-Regulator Connector

I Rectifier-Regulator J Oil SentryTM Kill (Green) K

Violet B+

L

Solenoid Shift Starter Assembly

M Starter Solenoid Tang N Starter Solenoid Stud O

Fuse

P

Blue

Q

Alternate Ignition Kill (­)

R

White

S Accessory Terminal (+) T

Yellow

U

Ignition Kill

V

Red

W

Carburetor

X Carburetor Solenoid

Y

Black (Ground)

Z Intake Manifold Screw AA

AC Oil SentryTM Light AD

Connector

AE

AG

Accessory

AH

Battery

AI

AK Key Switch Ground AL

Rectifier

AM

AO Battery Negative

Black
Magneto Starter Blue/Red

AB

Oil SentryTM Panel Light/Remote Light

AF

Key Switch

AJ

Ground

AN Battery Positive

CDI/MDI Ignition Systems Tests
NOTE: Ignition tester must be used to test ignition on these engines. Use of any other tester can result in inaccurate findings. Battery on unit must be fully charged and properly connected before performing tests (a battery that is hooked up or charged backward will crank engine but it won’t have spark). Be certain drive is in neutral and all external loads are disconnected.
Special Tools Required: Hand tachometer. Ignition tester. Multi-meter (digital).
Specifications Required: 0.76 mm (0.030 in.).
Test for Spark
NOTE: If 2 testers are available, testing can be performed simultaneously for both cylinders. However, if only 1 tester is available, 2 individual tests must be performed. Side not being tested must have spark plug lead connected or grounded. Do not crank engine or perform tests with 1 spark plug lead disconnected and not grounded, or permanent system damage may occur.
1. With engine stopped, disconnect 1 spark plug lead. Connect spark plug lead to post terminal of spark tester and attach tester clip to a good engine ground.
2. Crank engine over, establishing a minimum of 350-450 RPM, and observe tester(s) for spark.
3. Repeat spark test on opposite cylinder if cylinders are being tested individually.

Condition
Both cylinders have good spark but engine runs poorly or existing plug condition is questionable.
1 cylinder has good spark and other cylinder has no or intermittent spark.
Spark on both cylinders but power is suspect.

Possible Cause Spark Plug(s)
Ignition Sheared Flywheel Key

Conclusion Install new spark plug(s) and retest engine performance.
Test ignition modules and connections. Check for broken key.

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61

Electrical System

Test Ignition Systems NOTE: If engine starts or runs during testing, you may need to ground kill lead to shut it down. Because you have
interrupted kill circuit, it may not stop using switch.
Isolate and verify trouble is within engine.
1. Locate connectors where wiring harnesses from engine and equipment are joined. Separate connectors and remove white kill lead from engine connector. Rejoin connectors and position or insulate kill lead terminal so it cannot touch ground. Try to start engine to verify whether reported problem is still present.

Condition Problem goes away.
Problem persists.

Possible Cause Electrical System
Ignition or Electrical System

Conclusion
Check key switch, wires, connections, safety interlocks, etc.
Leave kill lead isolated until all testing is completed.
Identify white kill lead of engine wiring harness connector. Establish a connection to a known good ground location. Engine should kill completely. If not or only one cylinder is affected, test ignition modules and white kill lead connection.

Check CDI/MDI Ignition Modules and Connections 1. Remove blower housing from engine. Inspect kill wire for any damage, cuts, or shorts to engine or ignition module
body.
2. On MDI adjustable timing engines, ensure that both modules are correctly installed with flat side of module out/ towards you.
3. If testing identifies one ignition module does not function, disconnect white kill wire from both ignition modules and retest them with a spark tester as described in Test for Spark on previous page. If both ignition modules are found to spark with white kill wire removed, test white kill wire for short to ground. If not shorted to ground, connect white kill wire to one ignition module only and retest for spark. Repeat single wire connection test on second ignition module. If test results find that both ignition modules spark with white wire connected to single module only (both modules tested individually) but only one will spark when white wire is connected between both ignition modules, processor in one module is bad. Both ignition modules should be replaced if this condition is found.

Condition
All checks are OK but module has no spark or fails to advance.

Possible Cause Ignition Module

Conclusion Replace affected module.

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Electrical System
Wiring Diagram-15/20/25 Amp Regulated Battery Charging System with Variable Ignition Timing SMARTSPARKTM

F

D

EF G

A B
C

C

E

D

L

KJ H

Z I
AT

AA

AB

M

J

AC W

K AT
X

V UT

A

RN

K S

WY W

AD

O

T W

AG

Q P

T

AF

AJ AI AH

AE

AQ

AP

AP AO AH

AL

AK

AM W K

AS

AR

W T
AN

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63

Electrical System

A Oil Pressure Switch B Oil SentryTM (Green) C

E

Trigger

F

Ignition Module

G

I

Module Speed Advance 22, 25 HP

J

Brown

K

Spark Plug(s) Flywheel Stator
Assembly
Yellow

D

Kill

H

22, 25 HP SmartSparkTM Ignition

Yellow on Analog

L SAMs Pink on Digital

SAMs

M

Rectifier-Regulator Connector

N

Rectifier-Regulator

O Oil SentryTM Kill (Green) P

Solenoid Shift Starter Assembly

Q

Violet (B+)

R

Alternate Ignition Kill (­)

S Accessory Terminal (+) T

White

U

Ignition Kill

V

Smart-SparkTM

W

Y

Solenoid Lead

Z Intake Manifold Screw AA

Red Black

X

Carburetor

AB

Oil SentryTM Panel Light/Remote Light

AC Oil SentryTM Light AD

Connector

AE

AG

Accessory

AH

Battery

AI

Magneto Starter

AF

Key Switch

AJ

Ground

AK Key Switch Ground AL

Rectifier

AM

Blue/Red

AN Battery Positive

AO Battery Negative AP

Blue

AQ

Fuse

AR Starter Solenoid Stud

AS Starter Solenoid Tang AT Black (Ground)

Smart-SparkTM Advance Ignition System SadMvAaRncTe-S. APAtyRpKicTMaleaqpupiplipceadtioenngcoinnessisutstiloizfefoalnloweliencgtrcoonmicpcoanpeanctisti:ve discharge ignition system with electronic spark
1 magnet assembly which is permanently affixed to flywheel. 2 electronic capacitive discharge ignition modules which mount on engine crankcase. 1 spark advance module which mounts to engine shrouding. 1 12 volt battery which supplies current to spark advance module. 1 kill switch (or key switch) which grounds spark advance module to stop engine. 2 sp

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