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TRUCK SERVICE MANUAL
TM 5-4210-230-14&P-1
ADJUSTMENT PROCEDURE
If the fuel level is too high or low, install the sight plug, drain
the fuel bowl by loosening one lower retaining bolt from the
fuel bowl and drain the fuel into a suitable container. Install
the bolt and the fuel level sight plug and start the engine to fill
the fuel bowl. Check the fuel level again before altering the
float setting. This will eliminate the possibility of foreign
material causing a temporary flooding condition.
If the fuel level is still high or low, loosen the lock screw on the
top of the fuel inlet seat and turn the adjusting nut in or out to
correct the fuel level. 1/6 turn of the adjusting nut equals
approximately 3/64" in fuel level. Remove the sight plug and
recheck the fuel level. Repeat the foregoing procedure until
the correct fuel level is obtained.
Figure 52 Adjusting Fuel Level
It is important that the fuel level be maintained to
specifications, as the fuel level is a part of the carburetor
calibration.
CAUTION:
Do not loosen the lock screw or attempt to
adjust the fuel level with the sight plug
removed and the engine running, as this
creates a fire hazard.
Fast Idle Adjustment
Idle speed and fuel mixture settings must be made with the
engine at normal operating temperature, parking brake
applied
and
choke
open.
See
"Specifications"
for
transmission shift selector position and air conditioner switch
settings.
When making carburetor adjustments, disconnect vacuum
hose from vapor storage canister and plug end of hose. After
idle adjustments have been made, remove plug and reconnect
hose to canister. To compensate for fuel and temperature
variations
when
setting
idle
mixture,
observe
these
precautions:
a. Do not idle engine continuously for more than three
minutes at one time.
b. After each three minutes of idling increase engine speed to
2000 RPM for one minute.
c. Continue with idle adjustment procedure. Do not idle
engine for more than three minutes without repeating Step "b".
It is imperative that the precautions outlined above be
followed on engines equipped with road speed controlled
spark advance systems where extended idling could permit
sufficient increase in engine coolant temperature to activate
high temperature vacuum control valve and thereby affect
engine timing and idle speed.
Fast idle adjustment is performed as follows:
1. Shut off engine, remove air cleaner, connect tachometer of
known accuracy.
2. Depress accelerator pedal to floor. Close choke and
release accelerator pedal.
3. Remove curb idle stop screw and spring, reinstall idle
stop screw without spring (See Fig. 53).
Figure 53 Curb Idle Speed Screw and Spring
CGES-125-T Page 35
PRINTED IN UNITED STATES OF AMERICA
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