Chevrolet 1977 light duty truck, Service Manual

Page: 534 / 861

ELECTRIC
C A M
FOLLOWER
Fig. 6 C -l-M o d e l 1ME C arburetor-Rear View
pe rfo rm a n c e d u rin g m oderate to heavy acceleration and
at higher engine speeds.
T he idle system, on certain models, incorporates a
hot idle com pensator (A.T. only) to m a in ta in smooth
engine idle du rin g periods o f extreme hot engine
operation.
The model 1ME incorporates an integral autom atic
choke system which uses an d electrically heated choke
coil. The vacuum d ia p h ra g m unit is m ounted externally
on the air horn and connects to the thermostatic coil
lever through a connecting line.
The electric choke coil is contained in a choke
housing m o u n ted on a bracket attached to the float bowl.
A n integral, p leated-paper fuel inlet filter is
m ounted in the fuel bowl behind the fuel inlet nut to
give m a x im u m filtraton o f incom ing fuel. A check valve
on light duty emissions is used in the filter inlet to
prevent fuel d ra in in g fro m the fuel system after roll­
over.
O th e r features o f the M onojet c arburetor include an
a lu m in u m throttle body for decreased weight and
im proved h eat distribution an d a thick throttle body to
bowl insulator gasket to keep excessive engine heat from
Fig. 6C -2-M odel 1ME C arburetor Id e ntifica tio n
the float bowl. The c arburetor has internally balanced
venting through a vent hole in the air horn, which leads
from the float bowl into the bore ben eath the air cleaner.
The carburetor model identification is stam ped on a
vertical portion o f the float bowl, adjacent to the fuel
inlet nut (Fig. 6C-2).
If replacing the float bowl, follow the m a n u fa c tu r­
e r ’s instructions contained in the service package so that
the identification n u m b e r can be transferred to the new
float bowl.
An electrically operated idle stop solenoid is used on
all models.
Dual throttle return springs are used on all
carburetors.
The throttle lever has a spun-in plastic bushing, this
is used as the bearing surface for the dual throttle return
springs.
N O TE: The spun-in plastic return spring bushing
will w ith s ta n d n o rm a l c lean in g tim e in an
approved cold im m ersion type c arburetor cleaner.
The bushing is not serviced separately and should
not be removed from the carburetor throttle lever.
A n Exhaust G as Recirculation system (E G R ) is used
on light duty emission and heavy duty emission 454 CID
Calif, to control oxides o f nitrogen. The vacuum supply
port necessary to operate the recirculation valve is
located in the throttle body and connects through a
channel to a tube which is located at the top o f the air
horn casting. See Idle System (Fig. 6C-4) for port
location and operation.
Six basic systems o f operation are used: float, idle,
main metering, power enrichment, p u m p and choke. 6C-
3 through 9).