General Description - Pontiac FIREBIRD 1972 Service Manual

ENGINE FUEL 6B- 13
GENERAL DESCRIPTION
The Monojet carburetor is a single bore downdraft carbu-
retor using a triple venturi in conjunction with a plain tube
nozzle.
The main venturi is 1 5/16" in diameter and the throttle
bore is 1 11/16".
Fuel flow through the main metering system is controlled
by a main well air bleed and a variable orifice jet. A power
enrichment system is used to provide good performance
during moderate to heavy accelerations and at higher en-
gine speeds.
The idle system incorporates a hot idle compensator on
models equipped with automatic transmission, to main-
tain smooth engine idle during periods of extreme hot
engine operation
The model MV incorporates an automatic choke system.
The vacuum diaphragm unit is no longer an integral part
of the air horn and has been mounted externally on the air
horn and connects to the thermostatic coil lever through
a connecting link.
The automatic choke coil is manifold mounted and con-
nects to the choke valve shaft by a rod.
An integral, pleated-paper fuel inlet filter is mounted in
the fuel bowl behind the fuel inlet nut.
Features of the Monojet carburetor include an aluminum
throttle body for decreased weight and improved heat
distribution and a thick throttle body to bowl insulator
gasket to keep excessive engine heat from the float bowl.
The carburetor has internally balanced venting through a
vent hole in the air horn, which leads from the float bowl
into the bore beneath the air cleaner. A pressure relief
valve system is incorporated in the air horn, which vents
vapors externally during hot engine operation.
The carburetor part number is stamped on a vertical sec-
tion of the float bowl, next to the fuel inlet nut (Fig.
6B-13). When replacing the float bowl assembly, follow
the manufacturer's instructions contained in the service
package so that the part number can be transferred to the
new float bowl.
An electrically operated idle stop solenoid has been added
to the carburetor float bowl and replaces the normal idle
stop screw. The idle stop solenoid is used in conjunction
with the combination emission control valve (C.E.C.
valve). The idle stop solenoid controls the slow engine idle
speed. The C.E.C. valve, when energized through the
transmission, acts as a throttle stop by increasing idle
speed during high gear operation of the engine, which
helps in controlling overrun emissions during decelera-
tion. The C.E.C. valve also provides full spark vacuum
advance during high gear operation and is de-energized in
the lower gears and at idle for retarded spark timing dur-
L
ASSEM.
PLANT CODE
L
DAY OF THE YEAR
Fig. 6B-13 M V Carburetor Identification Location
ing this period. As mentioned, the normal idle speed set-
ting is made by adjusting the electrically operated idle stop
solenoid.
The idle mixture screw has a limiter cap installed and no
adjustment will be ,provided on the vehicle. The mixture
screw will be pre-set at the factory and capped and no
further adjustment should be required except during the
cleaning and overhaul.
An overhaul idle mixture adjustment procedure will be
provided, should the idle mixture needle need replacement
or the mixture channels cleaned during the overhaul proc-
ess. A new red idle mixture needle limiter cap will be
provided in the overhaul kit.