Adjustments On Car; Periodic Service; Overhaul And Adjustment - Pontiac FIREBIRD 1972 Service Manual

6B-68 1972 PONTIAC SERVICE MANUAL
the thermostatic coil is completely relaxed, at which point
the choke valve is wide open.
When the engine is thoroughly warm, the choke coil pulls
the intermediate choke lever completely dqwn and allows
the fast idle cam to rotate so that the cam follower drops
off the last step of the fast idle cam, allowing the engine
to run at normal speeds. When the choke moves toward
the up position, the end of the rod strikes a tang on the
air valve lock-out lever. As the rod moves to the end of
its travel, it pushes the lock-out tang upward and unlocks
the air valve.
To reduce friction and alleviate choke binding, the choke
shaft and intermediate choke shaft are teflon coated.
The choke system is equipped with an unloader mech-
anism which is designed to partially open the choke valve,
should the engine become loaded or flooded during the
starting period. To unload the engine, the accelerator
pedal should be depressed so that the throttle valves are
held wide open. A tang on a lever on the choke side of the
primary throttle shaft contacts the fast idle cam and
through the intermediate choke shaft forces the choke
valve slightly open. This allows extra air to enter the
carburetor bores and pass on into the engine manifold and
engine cylinders to lean out the fuel mixture so that the
engine will start.
ADJUSTMENTS ON CAR
All 4MV adjustments can be performed on the car. With
the exception of the idle speed and mixture adjustment
Carburetor
Model Number
Calif. or
Non Calif.
Both
Both
Both
Both
Both
--
A/C or
Non A/C
Both
Both
Both
Both
Both
Engine-Trans.
Usage
455 Auto. (Exc. H.0.i
400 Man.
400 Auto.
455 H.O. Auto.
455 H.O. Man.
(See section 6D), all adjustments are included in the
OVERHAUL AND ADJUSTMENTS procedure.
PERIODIC SERVICE
There are no periodic services required on the 4MV carbu-
retor; however, choke linkage, choke valve and levers and
pump linkage should be kept free of dirt and gum so that
they will operate freely. Do not oil any of the external
linkage.
The integral fuel filter in the carburetor float bowl should
be cleaned and replaced periodically. Normal recommen-
dations are that it be cleaned or replaced during the nor-
mal engine tune-up or between approximately 10,000 to
12,000 miles. This will, of course, vary dependent upon
fuel contamination.
OVERHAUL AND ADJUSTMENTS
Flooding, stumble on acceleration and other performance
The following is a step-by-step sequence by which the
complaints are, in many instances, caused by the presence
4MV carburetor may be completely disassembled and
of dirt, water or other foreign matter in the carburetor. To
reassembled. Adjustments may be made and various parts
aid in diagnosing the cause of the complaint, the carbu-
of the carburetor may be serviced without completely
retor should be carefully removed from the engine without
disassembling the entire unit.
draining the fuel from the bowl. The contents of the fuel
bowl may then be examined for contamination as the
NOTE: Place carburetor on proper holding fix-
carburetor is disassembled. ture.