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6C-10
1977 PONTIAC SERVICE MANUAL
VACUUM Dl AP
VACUUM C H A M 6
HOSE TO CANlS
VACUUM Dl AP
140
C.I.D.
@
Fig. 6C-15 Bowl Vent
c
Fig. 6C-16 Vacuum Break
thermostatic coil for greater choke valve opening when leaner
air/fuel
mixtures
are
desired
at
warmer
ambient
temperatures.
NOTE: Ground contact for the electric choke is
provided by a metal plate located at the rear of the choke
assembly. D O NOT INSTALL A CHOKE COVER
GASKET BETWEEN T H E ELECTRIC CHOKE
ASSEMBLY A N D T H E CHOKE HOUSING.
The electric choke assembly is indexed properly by
aligning the scribe mark on the front cover with the specified
index mark on the choke housing. (See Carburetor
Adjustments)
The electric choke and thermostatic coil are serviced as
a complete assembly.
VACUUM BREAK DELAY L4-151
ENGINE
The L4-151 engine vacuum break is controlled by a
vacuum delay valve (Fig. 6C-18). This valve causes delayed
application of manifold vacuum to the carburetor vacuum
break unit when the engine starts.
The valve incorporates a check valve feature which
allows a quick release of vacuum in the vacuum break unit
should a stall occur or during engine shut down. This allows
the choke blade to close quickly.
Refer to on-car service in this section for functional test
of the vacuum delay valve. Refer to Section 6E, for proper
installation of the valve.
SECONDARY V A C U U M BREAK L4-140
CALIFORNIA A N D HIGH ALTITUDE
The L4-140 California or high altitude certified vehicle
is equipped with a secondary vacuum break designed to pull
the choke blade to a wider position after the engine has
reached 105°F. coolant temperature. There are two modes of
operation dependent upon initial engine coolant temperature
as follows:
1. Engine Coolant Temperature Below 105°F.
The coolant thermal vacuum switch is closed and the
actuator is de-energized. When the specified coolant
temperature is reached, the TVS opens and the activator
energizes, pulling the choke blade to a second vacuum break
position.
2. Engine Coolant Temperature Above 105°F.
The TVS is open and the actuator energizes immediately
after the engine starts.
Refer to on-car service in this section for functional test
of the TVS. Refer to Section 6E, for proper installation of the
vacuum hoses.
The secondary vacuum break TVS also controls the
distributor vacuum advance. Service of the vacuum advance
portion of the valve is in Section 6D.
DIAGNOSIS
Refer to engine performance diagnosis, Section 6, and/or
cleaning and inspection under unit overhaul in this section.
ON-CAR SERVICE
Carburetor Choke and Hoses
Check choke mechanism and vacuum break for proper
operation at the recommended maintenance intervals. Any
binding condition which may have developed due to
petroleum gum formation on the choke shaft or from damage
should be corrected. Check carburetor choke hoses for proper
connection, cracking, abrasion or deterioration and correct
or replace as necessary.
Choke Check Procedure
1. Remove air cleaner. With engine off, hold throttle half
open. Open and close choke several times. Watch linkage to
be certain all links are connected and there are no signs of
damage.
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