Carburetor Model 1Mef - GMC G Service Manual

6C1-2 CARBURETORS

CARBURETOR MODEL 1MEF

DESCRIPTION
Model 1MEF is a single bore downdraft carburetor using
a triple venturi along with a discharge tube nozzle (figure 1).
Figure 1 — 1MEF Carburetor
A power valve piston assembly and metering rod control
the fuel flow in the main metering and power systems of the
carburetor. The tapered metering rod is attached to the
power piston and moves in a fixed metering jet to provide
the fuel flow for varying engine demands. On 1MEF carbu­
retors, a factory-set metering rod adjusting screw controls
the position of the metering rod in the jet. This screw is
located in the air horn and should not be turned as this
could result in engine damage or increased exhaust
emissions.
Model 1MEF incorporates an integral automatic choke
system, which uses an electrically heated choke coil. The
vacuum diaphragm unit is mounted externally on the air
horn and connects to the thermostatic coil lever through a
connecting link.
The electrical choke coil is contained in a choke housing,
which is mounted on a bracket attached to the float bowl.
Special rivets are installed to retain the factory setting of the
choke coil and provide a non-adjustable design.
An integral, pleated-paper fuel inlet filter is mounted in
the fuel bowl behind the fuel inlet nut to give maximum
filtration of incoming fuel. A check valve is used in the filter
inlet to prevent fuel drainage from the fuel system after
rollover.
To improve hot engine starting and meet evaporative
emission requirements, fuel vapors from the carburetor
bowl are vented to a vapor canister on some models. A
tube is added to the air horn to connect the air horn and
canister.
Other features of the carburetors include an aluminum
throttle body for decreased weight and improved heat distri­
bution. A thick throttle body to bowl insulator gasket keeps
excessive engine heat from the float bowl.
All 1 MEF models have seals added in the float bowl to
seal the power piston drive rod and the pump lever. This
prevents fuel vapors from escaping to atmosphere. During
unit repair, the seals and retainer, where used, must be
removed prior to immersion of the float bowl in carburetor
cleaner.
The carburetor model identification is stamped on a ver­
tical portion of the float bowl, adjacent to the fuel inlet nut
figure 2).
B
C
D
E
F
A. M odel Num ber
B. Day Of Year
C. Source Code
D. Year
E. A ssem bly Plant Code
F. S hift Identification
Figure 2 — Carburetor Identification
If replacing the float bowl, follow the manufacturer's
instructions contained in the service package so that the
identification number can be transferred to the new float
bowl.
Dual throttle return springs and an electrically operated
idle stop solenoid are used on all carburetors.
The throttle lever has a spun-in plastic bushing which is
used as a bearing surface. The bushing will withstand nor­
mal cleaning time in an approved cold immersion type car­
buretor cleaner. The bushing is not serviced separately and
should not be removed from the carburetor throttle lever.
Six basic systems of operation are used (figures 3
through 8).
• Float
• Pump
• Main Metering
• Power
• Choke
• Idle
B-06647