22
Fuel System
KohlerEngines.com
18 690 06 Rev. --
Troubleshooting-Carburetor Related Causes
Condition
Possible Cause
Conclusion
Engine starts hard, runs rough, or
stalls at idle speed.
Low idle speed improperly adjusted.
Adjust idle speed screw or clean
carburetor.
Engine runs rich (indicated by black,
sooty exhaust smoke, mis
fi
ring, loss
of speed and power, governor
hunting, or excessive throttle
opening).
Clogged air cleaner.
Clean or replace air cleaner.
Choke partially closed during
operation.
Check choke lever/linkage to ensure
choke is operating properly.
Dirt under fuel inlet needle.
Remove needle; clean needle and
seat and blow with compressed air.
Bowl vent or air bleeds plugged.
Clean vent, ports, and air bleeds.
Blow out all passages with
compressed air.
Leaky, cracked, or damaged
fl
oat.
Submerge
fl
oat to check for leaks.
Engine runs lean (indicated by
mis
fi
ring, loss of speed and power,
governor hunting, or excessive
throttle opening).
Intake air leak.
Check if carburetor is loose or one of
intake gaskets is leaking.
Idle holes plugged; dirt in fuel delivery
channels.
Clean main fuel jet and all passages;
blow out with compressed air.
Fuel leaks from carburetor.
Float damaged.
Submerge
fl
oat to check for leaks.
Replace
fl
oat.
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.
Carburetor Circuits
Float
Fuel level in bowl is maintained by
fl
oat and fuel inlet
needle. Buoyant force of
fl
oat stops fuel
fl
ow when
engine is at rest. When fuel is being consumed,
fl
oat will
drop and fuel pressure will push inlet needle away from
seat, allowing more fuel to enter bowl. When demand
ceases, buoyant force of
fl
oat will again overcome fuel
pressure, rising to predetermined setting and stop
fl
ow.
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
fi
xed 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 air
fl
ow where
further mixing of fuel and air occurs. This mixture is then
delivered to combustion chamber. Carburetor has a
fi
xed
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 are not
adjustable.
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 1800 RPM.
1. Place throttle control into idle or slow position. Turn
low idle speed adjusting screw in or out to obtain
allow idle speed of 1800 RPM (± 75 RPM).
