Kohler Command PRO CH750 [27/92] Fuel system
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Kohler Command PRO CH750 [27/92] Fuel system

Kohler Command PRO CH640 [27/92] Fuel system
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 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.
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
BB
CC
ED
AA
A Rich B Lean
C Midpoint D Left Side
E Right Side
NOTE: Engines will have fi xed 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.
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.
Fuel System
2724 690 06 Rev. K KohlerEngines.com

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