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5.6
Section 5
Fuel System and Governor
Figure 5-4. Pre-Compliance Carburetor with Low
Idle Adjustment.
1. With the engine stopped, turn the low idle fuel
adjusting needle in clockwise until it bottoms
lightly.
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.
2. Now turn the adjusting needle out
counterclockwise 1-1/2 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. Choke plate and shaft assembly
is spring loaded. Check to make sure
plate moves freely and is not binding and
affecting idle fuel delivery.
4. Place the throttle control into the “idle” or “slow”
position. Turn the low idle speed adjusting screw
in or out to obtain a low idle speed of 1200 RPM
(± 75 RPM). 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. Turn the low idle fuel adjusting needle in (slowly)
until engine speed decreases and then back out
approximately 3/4 turn to obtain the best low
speed performance.
6. Recheck the idle speed using a tachometer and
readjust the speed as necessary.
Float
It is not necessary to remove the carburetor from the
engine to check and adjust the float.
1. Remove the air cleaner and breather hose. Refer
to Section 9 – ‘‘Disassembly”.
Carburetor Adjustments
General
In compliance with government emission standards,
the carburetor is calibrated to deliver the correct air-to-
fuel mixture to the engine under all operating
conditions. The high-speed mixture is preset and
cannot be adjusted. Pre-compliance carburetors
contain a low idle fuel adjusting needle, on “certified”
compliance carburetors, both the low and high speed
mixture circuits are pre-established and cannot be
adjusted. The low idle speed (RPM) is the only
adjustment available. See Figures 5-4 and 5-5.
Low Idle Speed
Adjustment
Low Idle Fuel
Adjusting Needle
Main Jet
Location
Figure 5-5. “Certified” Compliance Carburetor.
NOTE: Carburetor adjustments should be made only
after the engine has warmed up.
Adjusting Low Idle Speed and Fuel (Some Models)
To adjust the carburetor idle speed, see Figure 5-4 and
follow these steps.
Low Idle
Speed
Adjustment
Fuel Shut-Off
Solenoid (Main
Jet Location)