Pontiac FIREBIRD 1972 Service Manual page 716

6B-62 1972 PONTIAC SERVICE MANUAL
fuel begins to discharge from the lower idle air bleed holes
and continues to do so throughout operation of the part
throttle to wide open throttle ranges, supplementing the
main discharge nozzle delivery.
The idle needle holes and off-idle discharge ports continue
to supply sufficient fuel for engine requirements until air
velocity is high enough in the venturi area to obtain effi-
cient fuel flow from the main metering system.
HOT IDLE COMPENSATOR
The hot idle compensator used on all V-8 automatic trans-
mission models (except Ram Air) is located in a chamber
at the rear of the carburetor float bowl, adjacent to the
secondary bores. Its purpose is to offset enrichening ef-
fects caused by excessive fuel vapors during hot engine
operation.
The compensator consists of a thermostatically controlled
valve, a bi-metal strip which is heat sensitive, a valve
holder and bracket. The valve closes off an air channel
which leads from a hole in the top of the air horn, just
beneath the air cleaner, to a point below the secondary
Normally the compensator valve is held closed by tension
of the bi-metal strip. During extreme hot engine operat-
ion, excessive fuel vapors entering the engine manifold
cause richer than normally required mixtures, resulting in
rough engine idling and stalling. At a predetermined tem-
perature, when extra air is needed to offset the enrichening
effects of fuel vapors, the bi-metal strip bends and unseats
the compensator valve. This uncovers the air channel
leading from the valve chamber to the point below the
throttle valves. This allows enough air to be drawn into
the engine manifold to offset the richer mixtures and
maintain a smooth engine idle. When the engine cools and
the extra air is not needed, the bi-metal strip closes the
valve and operation returns to normal mixtures.
The compensator valve assembly is held in place by the
dust cover over the valve chamber. A seal is used between
the compensator valve and the float bowl casting.
In order to insure proper idle adjustment when the engine
is hot, the compensator valve must be closed. To check
this, a finger may be held over the compensator air inlet
channel located on top of the air horn. If no drop in engine
RPM is noted on the tachometer, the valve is closed. If the
valve is open, plug the hole or cool engine down to a point
throttle valves.
where the valve is closed for proper idle adjustment.
AIN DISCHARGE
OST VENTURll
MAlN VENTURI
MAlN FUEL WEL
MAlN METERING
MAlN VENTURI
MAlN FUEL WEL
JET
/
VACUUMCHANNEL
-
Fig. 68-78 Main Metering S y s t e m