Model CH750
CH750 engines use a Keihin BK two-barrel carburetor
with fixed main jets and fixed or limiter-equipped low
idle fuel adjusting needles. See Figure 20. Adjustments
are made as follows.
Figure 20. Keihin Two-Barrel Carburetor.
Low Idle Speed (RPM) Adjustment
1. Low Idle Speed (RPM) Setting: Place the throttle
control into the idle or slow position. Set the low
idle speed to 1200 RPM* (± 75 RPM) by turning
the low idle speed adjusting screw in or out.
Check the speed using a tachometer.
*NOTE: The actual low idle speed depends on the
application. Refer to the equipment
manufacturer's recommendations. The low
idle speed for basic engines is 1200 RPM. To
ensure best results when setting the low idle
fuel needle, the low idle speed should be 1200
RPM (± 75 RPM).
Low Idle Fuel Adjustment
NOTE: Engines will have fixed low idle or limiter
caps on the two idle fuel adjusting needles.
Step 3 can only be performed within the
limits allowed by the cap. Do not attempt to
remove the limiter caps.
1. Start the engine and run at half throttle for 5 to
10 minutes to warm up. The engine must be
warm before doing steps 2, 3, and 4.
2. Place the throttle control into the idle or slow
position. Adjust the low idle speed to 1200 RPM*
Follow the Adjusting the Low Idle Speed (RPM)
procedure.
3. Low Idle Fuel Needle(s) Setting: Place the
throttle into the idle or slow position.
a. Turn one of the low idle fuel adjusting needles
out (counterclockwise) from the preliminary
setting until the engine speed decreases (rich).
Note the position of the needle. Now turn the
16
Low Idle Fuel Adjusters
(with limiters)
Low Idle Speed (RPM)
Adjustment Screw
Fuel Solenoid
adjusting needle in (clockwise). The engine
speed may increase, then it will decrease as
the needle is turned in (lean). Note the
position of the needle. Set the adjusting needle
midway between the rich and lean settings.
See Figure 21.
b. Repeat the procedure on the other low idle
adjustment needle.
4. Recheck/adjust the Low Idle Speed (RPM), to the
specified setting.
Lean
Adjust to
Midpoint
Rich
Left Side
Figure 21. Optimum Low Idle Fuel Settings.
Models with Governed Idle System
An optional governed idle control system is supplied
on some CH750 engines. The purpose of this system is
to maintain a desired idle speed regardless of ambient
conditions (temperature, parasitic load, etc.) that may
change. Engines with this feature contain a small
secondary spring connected between the governor
lever and the lower adjustment tab of the main
bracket. See Figure 18. Refer to the same adjustment
procedure covered in Models with Governed Idle
System for the CH18-740 models on page 15, when
adjustments are required.
Electronic Fuel Injection (EFI) System
The EFI system is a complete, electronically-controlled
fuel management system, designed to deliver a
precisely controlled fuel flow under all operating
conditions. The electronic control unit (ECU), the brain
of the system, automatically adjusts fuel delivery and
ignition timing based upon load, speed, operating
temperature, and exhaust emission levels. The low
idle speed is the only manual adjustment possible.
The ECU continuously monitors operation of the EFI
system. If it detects a problem or fault within the
system, it will illuminate the malfunction indicator
light (MIL), which is mounted in view of the operator.
This is a signal that normal, programmed operation
has been affected, and service by an authorized Kohler
Engine Dealer is required.
Lean
Adjust to
Midpoint
Rich
Right Side
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