Kohler Comand Pro CH1000, Service Manual, Page: 35 / 142

5.5
Section 5
Fuel System and Governor
5
Slow & Mid-Range Circuit:
At low speeds the engine operates only on the slow
circuit. As a metered amount of air is drawn through
the slow air bleed jets, fuel is drawn through the two
main jets and further metered through the slow jets.
Air and fuel are mixed in the body of the slow jet and
exit to the transfer port. From the transfer port the
air fuel mixture is delivered to the idle progression
chamber. From the idle progression chamber the
air fuel mixture is metered through the idle port
passages. At low idle when the vacuum signal is
weak, the air/fuel mixture is controlled by the se
tt ing
of the idle fuel adjusting screws. This mixture is then
mixed with the main body of air and delivered to
the engine. As the thro
tt le plate opening increases,
greater amounts of air/fuel mixture are drawn in
through the
fi xed and metered idle progression holes.
As the thro tt le plate opens further the vacuum signal
becomes great enough so the main circuit begins to
work.
Main (High-Speed) Circuit:
At high speeds/loads the engine operates on the main
circuit. As a metered amount of air is drawn through
the four air jets, fuel is drawn through the main jets.
The air and fuel are mixed in the main nozzles and
then enter the main body of air
fl ow, where further
mixing of the fuel and air occurs. This mixture is then
delivered to the combustion chamber. The carburetor
has a
fi xed main circuit; no adjustment is possible.
Carburetor Adjustments
Adjustment
NOTE: Carburetor adjustments should be made only
a ft er the engine has warmed up.
The carburetor is designed to deliver the correct
fuel-to-air mixture to the engine under all operating
conditions. The main fuel jet is calibrated at the
factory and is not adjustable*. The idle fuel adjusting
needles are also set at the factory and normally do not
need adjustment.
*NOTE: Engines operating at altitudes above
approximately 1219 m (4000 ft .) may require
a special high altitude main jet. Refer to High
Altitude Operation earlier in this section.
If, however, the engine is hard-starting or does not
operate properly, it may be necessary to adjust or
service the carburetor.
Below is a simple test, made with the engine o ff , that
can determine if the solenoid is functioning properly:
1. Shut o ff fuel and remove the solenoid from the
carburetor. When the solenoid is loosened and
removed, gas will leak out of the carburetor.
Have a container ready to catch the fuel.
2. Wipe the tip of the solenoid with a shop towel or
blow it o ff with compressed air, to remove any
remaining fuel. Take the 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 o
ff .
3. Be sure the power source is switched OFF .
Connect the positive power source lead to the red
lead of the solenoid. Connect the negative power
source lead to the solenoid body.
4. Turn the power source ON and observe the pin in
the center of the solenoid. The pin should retract
with the power on and return to its original
position with the power
OFF . Test several times
to verify operation.
Carburetor Details
The Keihin BK two-barrel carburetor is a side-dra ft
design. The circuits within the carburetor function as
described following:
Float Circuit:
The fuel level in the bowl is maintained by the fl oat
and fuel inlet needle. The buoyant force of the fl oat
stops fuel fl ow when the engine is at rest. When
fuel is being consumed, the fl oat will drop and fuel
pressure will push the inlet needle away from the
seat, allowing more fuel to enter the bowl. When
demand ceases, the buoyant force of the
fl oat will
again overcome the fuel pressure, rising to the
predetermined se
tt ing and stop the fl ow.