Chevrolet 1977 light duty truck, Service Manual

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MODEL 2GC CARBURETOR
GENERAL DESCRIPTION
T h e M odel 2 G C carb u reto r (Figs. 6C-14 and 15) is
e q u ip p ed w ith a n integral choke attached to the throttle
body assembly.
All light duty emission models use a fuel inlet check
valve to shut off fuel flow to the carb u reto r float bowl to
prevent fuel leaks if a vehicle roll-over should occur.
All models (except C alifornia) use full vacuum for
distrib u to r advance obtained thro u g h a tube pressed into
the float bowl (choke side location " h " ). On C alifornia
models, tim ed vacuum for distributor advance is
supplied thro u g h this same tube (location "h").
A n Exhaust G a s Recirculation (E.G.R.) system is
used to meet emission requirem ents for oxides o f
N itro g e n (NOx). In addition, a cup restriction is added
in the float bowl beh in d the Exhaust G a s Recirculation
(E.G .R .) vacuum tube (location "j"), to delay E.G.R.
valve o p e ra tio n for im proved engine p erfo rm an ce as the
throttle valves are opened.
A electrically operated solenoid is used on all 2 G C
models e quipped with automatic transm ission and air
conditioning. The solenoid is used to m a in ta in p ro p er
idle speed w hen the air conditioning is in operation.
Fuel for the p u m p system is obtained through a hole
located in a raised cast-in boss on the floor o f the float
bowl which prevents the entry o f dirt into the accelerator
p u m p fuel inlet passage. The p u m p plu n g er head is
designed with an e x p an d er spring beneath the p u m p cup
to m ain tain good p u m p wall contact d u rin g p u m p
operation.
The end o f the p u m p plunger stem is upset in
m a n u fa c tu rin g to pro vide the "clipless" retain in g in
feature. The p u m p plunger assembly m ay be removed
from the in n e r lever by twisting upset end with small
pliers until it breaks. The service p u m p assembly has a
grooved end and is provided with a retaining clip.
T he c arburetor p a r t n u m b e r is stam ped on the flat
section o f the float bowl next to the fuel inlet nut. (Fig.
6C-17). W hen servicing the c arburetor unit, re fe r to the
O n-C ar Service section for pro p er procedures and
specifications.
Incorporated in the M odel 2 G C carb u reto r are six
basic systems. They are Float, Idle, M a in Metering,
Power, P um p and C hoke (Figs. 6C-17 through 23).