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Fuel System
KohlerEngines.com 20 690 01 Rev. F
These engines are equipped with either a Walbro or
Nikki fi xed main jet carburetor. Carburetors will have a
low idle speed adjustment screw, and either fi xed idle, or
a limiter cap on idle fuel adjustment needle.
Troubleshooting Checklist
When engine starts hard, runs rough, or stalls at low
idle speed, check these areas before adjusting or
disassembling carburetor.
1. Make sure fuel tank is fi lled with clean, fresh
gasoline.
2. Make sure fuel tank cap vent is not blocked and is
operating properly.
3. Make sure fuel is reaching carburetor. This includes
checking fuel shut-off valve, fuel tank fi lter screen,
in-line fuel fi lter, 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.
Troubleshooting-Carburetor Related Causes
Condition Possible Cause Conclusion
Engine starts hard, runs rough, or
stalls at idle speed.
Low idle fuel mixture/speed
improperly adjusted.
Adjust low idle speed screw, then
adjust low idle fuel needle.
Improper choke adjustment. Correct choke adjustment.
Engine runs rich (indicated by black,
sooty exhaust smoke, misfi ring, loss
of speed and power, governor
hunting, or excessive throttle
opening).
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.
Dirt under fuel inlet needle. Remove needle; clean needle and
seat and blow with compressed air.
Bowl vent or air bleeds plugged. Remove fuel bowl, low idle fuel
adjusting needle, and welch plugs.
Clean vent, ports, and air bleeds.
Blow out all passages with
compressed air.
Fuel bowl gasket leaks. Remove fuel bowl and replace
gasket.
Leaky, cracked, or damaged fl oat. Submerge fl oat to check for leaks.
Engine runs lean (indicated by
misfi ring, loss of speed and power,
governor hunting, or excessive
throttle opening).
Low idle fuel mixture is improperly
adjusted.
Adjust low idle fuel needle.
Idle holes plugged; dirt in fuel delivery
channels.
Remove fuel bowl, low idle fuel
adjusting needle, and welch plugs.
Clean main fuel jet and all passages;
blow out with compressed air.
Fuel leaks from carburetor. Dirt under fuel inlet needle. Remove fuel bowl, low idle fuel
adjusting needle, and welch plugs.
Clean vent, ports, and air bleeds.
Blow out all passages with
compressed air.
Float is cracked or damaged. Replace fl oat.
Bowl retaining screw gasket
damaged.
Replace gasket.
Bowl retaining screw loose. Torque screw to specifi cations.
Walbro 5.1-6.2 N·m (45-55 in. lb.) or
Nikki 10.8-12.8 N·m (96-113 in. lb.).