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15
Adjust Carburetor
Low Idle Speed (RPM) and Governed Idle
Adjustment
1. Low Idle Speed (RPM) Setting: Place the throttle
control into the idle or slow position. Hold the
governor lever away from carburetor so the
throttle lever is against the Idle Speed (RPM)
Adjustment Screw of carburetor. See Figure 26.
Set the low idle speed to 1200 RPM* (± 75 RPM)
by turning the low idle speed adjusting screw on
carburetor 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).
2. Release the governor lever and check that the
throttle lever is in the idle position. Turn the
governed idle (outer) adjustment screw on main
control bracket to obtain the equipment
manufacturer's recommended idle speed (1400-
1800 RPM). See Figure 27.
Governed Idle
Speed Screw
High Speed
Adjustment Screw
Lean
Rich
Adjust to
Midpoint
Lean
Rich
Adjust to
Midpoint
Left Side Right Side
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
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 28.
b. Repeat the procedure on the other low idle
adjustment needle.
4. Recheck/adjust the Low Idle Speed (RPM), to the
specified setting.
Figure 28. Optimum Low Idle Fuel Settings.
High Speed (RPM) Adjustment
The high speed RPM (inner) adjustment screw is
preset at the factory and normally does not need
readjustment.
Figure 27. Adjusting Governed Idle Speed Screw.
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.