Fuel Shut-Off Solenoid; Carburetor Adjustments; Carburetor Circuits; Low Idle Fuel Adjustment - Kohler CH940-CH1000 Service Manual

Fuel System and Governor

Fuel Shut-off Solenoid

Most carburetors are equipped with a fuel shut-off
solenoid. Solenoid is attached to fuel bowl. Solenoid has
a spring-loaded pin that retracts when 12 volts is applied
to lead, allowing fuel fl ow to main jets. When current is
removed pin extends blocking fuel fl ow.
Below is a simple test, made 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 it off
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.

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 & 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 two main jets and further
metered through slow jets. Air and fuel are mixed in
body of slow jet and exit to transfer port. From transfer
port air fuel mixture is delivered to idle progression
chamber. From idle progression chamber air fuel mixture
is metered through idle port passages. At low idle when
vacuum signal is weak, 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 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 four air jets,
fuel is drawn through main jets. Air and fuel are mixed in
main nozzles and then enter main body of airfl 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.
24

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. To ensure best results
when setting low idle fuel needle, low idle speed
should be 1200 RPM (± 75 RPM).
Low Idle Speed (RPM) Setting:
1. Place throttle control in idle or slow position.
2. Set low idle speed approximately 300 RPM less than
intended or specifi ed Governed Idle Speed, by
turning low idle speed adjusting screw in or out.
3. Check speed using a tachometer.
IMPORTANT: Governed Idle Speed Adjustment must
follow any resetting of Low Idle Speed.
4. If equipped, refer to Governed Idle Speed
Adjustment.

Low Idle Fuel Adjustment

Adjust to
Midpoint
Rich
Left Side
NOTE: Engines will have fi xed low idle or limiter caps
on two idle fuel adjusting needles. Step 3 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 Adjusting Low
Idle Speed (RPM) procedure.
2. Low Idle Fuel Needle(s) Setting: place throttle into
idle or slow position.
a. Turn one 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.
3. Recheck/adjust Low Idle Speed (RPM) to specifi ed
setting.
KohlerEngines.com
Lean
Adjust to
Midpoint
Rich
Right Side
62 690 01 Rev. C
Lean