General Description - Pontiac FIREBIRD 1972 Service Manual

6B-58 1972 PONTIAC SERVICE MANUAL
E N G I N E R U N S R O U G H , S U R G E S
PLUGGED OR DIRTY
PLUGGED. LOOSE OR
BENT. ALTERED OR IN-
CHECK IDLE SYSTEM FOR
CARBURETOR DIAGNOSIS CHART
MODEL 4MV
P O O R G A S M I L E A G E
-
LINKAGE FOR BINDING OR
I
CHECK POWER PISTON
LEAKS OR BEING PLUGGED
I
I
P O O R H I G H S P E E D P E R F O R M A N C E
-
CARBURETOR FLOODING
+
I
CHECK FLOAT NEEDLE FLOAT BENT, STICKING.
MISALIGNED. MISADJUSTED
DIRT. WEAR. DAMAGE,
LOOSENESS.
I
SPEED
PUMP DISCHARGE BALL NOT
SEATING. CHECK FOR DIRT,
DEFECTIVE SEAT OR DISCHARGE
1
SPRING
OPENING AT CARBURETOR
ADJUST THROTTLE LINKAGE
M A Y BE HARD OR BRITRE
GENERAL DESCRIPTION
The Quadrajet carburetor has two stages in operation. The
needle has a synthetic tip which gives added insurance
primary (fuel inlet) side has two small bores (1 3/8") with
against flooding problems caused by dirt.
a triple venturi equipped with plain tube nozzles. The
triple venturi stack up, plus the smaller primary bores,
A pleated paper fuel inlet filter is mounted in the fuel inlet
gives a more stable and finer fuel control in the idle and
casting, which is an integral part of the float bowl and is
economy ranges of operation. Fuel metering in the pri-
easily removed for cleaning or replacement.
mary side is accomplished with tapered metering rods
positioned by a manifold vacuum responsive piston.
Idle mixture adjustment limiters are used on all models.
The secondary side has two large bores (2 1/4"). Using the
air valve principle in the secondary side, fuel is metered
The idle mixture will be set at the factory and capped with
in direct proportion to the air passing through the second-
a plastic cap. No adjustment should be required in the
ary bores.
field unless complete overhaul of the carburetor is neces-
sary.
The fuel reservoir is centrally located to avoid problems
of fuel slosh, causing engine turn cut-out and delayed fuel
Variable and constant bleed purge ports have been added
flow to the carburetor bores. The float system uses a single
to the carburetor base for use in purging fuel vapors from
float pontoon for ease in servicing the unit. The float
the vapor collection canister.