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5.9
Section 5
Fuel System and Governor
5
Figure 5-6. Carburetor Adjustments.
2. Preliminary Settings: Turn the adjusting needle
out (counterclockwise) from lightly bottomed
2-1/4 turns.
3. Start the engine and run at half throttle for 5 to 10
minutes to warm up. The engine must be warm
before making final settings. Check that the
throttle and choke plates can fully open.
NOTE: The carburetor has a self-relieving
choke. The choke plate and shaft
assembly is spring loaded. Check to
make sure the plate moves freely and is
not binding, affecting idle fuel delivery.
4. Low Idle Speed 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).
5. Low Idle Fuel Needle Setting: Place the throttle
into the “idle” or “slow” position. Turn the low
idle fuel adjusting needle in (slowly) until engine
speed decreases and then back out approximately
3/4 to 1 turn to obtain the best low speed
performance.
6. Recheck the idle speed using a tachometer and
readjust the speed as necessary.
Models with Governed Idle System
An optional governed idle control system is supplied
on some 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 5-7.
The system requires an additional procedure for
setting the idle speed. If speed adjustments are
required proceed as follows.
1. Make any necessary speed or control adjustments
following the appropriate instructions covered in
this section.
2. Move the throttle control to the idle position.
Hold the governor lever away from the
carburetor, or hold the throttle lever so it is tight
against the idle speed adjusting screw, to negate
the governor activation. See Figure 5-8. Check the
speed with a tachometer and adjust it to 1500
RPM.
3. Release the governor lever and allow the engine
to return to the governed idle speed. Check it
with a tachometer against the equipment
manufacturers recommended idle speed.
Governed Idle Speed (RPM) is typically 300 RPM
(approximate) higher than the low idle speed. If
adjustment is necessary, bend the adjusting tab on
the speed control assembly to set. See Figure 5-7.
Low Idle Fuel
Adjustment
(Some Models)
Low Idle Speed
(RPM) Adjustment
NOTE: The tip of the idle fuel adjusting needle
is tapered to critical dimensions.
Damage to the needle and the seat in the
carburetor body will result if the needle
is forced.