Pontiac FIREBIRD 1972 Service Manual page 720

6B-66 1972 PONTIAC SERVICE MANUAL
AS PLUNGER MOVES UP
FUEL FLOWS PAST CUP
INTO PUMP WELL
PUMP PLUNGER DISCHARGE BALL RETAINER
Fig. 68-8 1 Pump System
It should be noted that the pump plunger is spring loaded.
The top pump duration spring is balanced with the bottom
pump return spring so that a smooth sustained charge of
fuel is delivered during acceleration.
The pump discharge check ball seats in the pump dis-
charge passage during upward motion of the pump
plunger so that air will not be drawn into the passage;
otherwise, a momentary acceleration lag could result.
During high speed operation, a vacuum exists at the pump
jets. A cavity just beyond the pump jets is vented to the
top of the air horn, outside the carburetor bores. This acts
as a suction breaker so that when the pump is not in
operation fuel will not be pulled out of the pump jets into
the venturi area. This ensures a full pump stream when
needed and prevents any fuel "pull over" from the pump
discharge passage.
CHOKE SYSTEM
The Quadrajet choke valve (Fig. 6B-82) is located on the
primary side of the carburetor. It provides the correct
air/fuel mixture enrichment to the engine for quick cold
engine starting and during the warm-up period. The air
valve is locked closed until the engine is thoroughly warm
and choke valve is wide open.
The choke system consists of a choke valve located in the
primary air horn bore, a vacuum diaphragm unit, fast idle
cam, connecting linkage, air valve lockout lever and a
thermostatic coil. The thermostatic coil is located on the
engine manifold and is connnected to the intermediate
choke shaft and lever assembly. Choke operation is con-
trolled by the combination of intake manifold vacuum, the
off-set choke valve, temperature and throttle position.
The thermostatic coil, located on the engine manifold, is
calibrated to hold the choke valve closed when the engine
is cold.
NOTE To close the choke valve, the primary
throttle valves have to be opened to allow the
fast idle cam follower to by-pass the steps on
the fast idle cam and come to rest on the highest
step of the fast idle cam.