Pontiac FIREBIRD 1972 Service Manual page 681

ENGINE FUEL 6B-27
WGD CARBURETOR
DESCRIPTION AND OPERATION OF WGD 2-BARREL CARBURETOR
GENERAL DESCRIPTION
The WGD Carter carburetor used on 350 Manual engines
is a 2-barrel, down draft, offset bowl type (Fig. 6B-3 1). It
contains a float system, low speed (idle) system, high
speed system, power system, accelerating system and pla-
teau choke assembly (automatic choke).
Air enters both barrels of carburetor through the air horn
which has one inlet and contains the choke valve. Fuel is
supplied to both barrels from one float chamber. The float
chamber is on the forward side of both barrels and con-
tains a single float and lever assembly which operates a
float needle or valve. The accelerating pump jet in each
barrel is supplied with fuel from one pump located in the
float chamber. The power systems of both barrels are
controlled by one vacuum piston and link.
Except as noted above, each barrel forms a complete car-
buretor system. Each barrel contains a low speed system
with a fixed adjustment screw, a high speed system with
a metering rod, an accelerating pump discharge jet, a
triple venturi and a throttle valve. The throttle valves of
both barrels are mounted in line on one shaft. The dual
construction combines the advantages of two carburetors
in one compact unit. The dual carburetor and dual intake
manifold provide more uniform distribution of fuel to all
cylinders than would be possible with one single barrel
carburetor.
OPERATION OF WGD FLOAT SYSTEM
Fuel enters the carburetor at the gasoline connection and
flows through the needle seat into the float chamber.
When the fuel reaches the prescribed level in float cham-
ber, the float presses the needle against its seat to shut off
the flow of fuel. Thereafter, the fuel is maintained at the
prescribed level by opening and closing of needle as re-
quired. The float chamber is vented internally through a
port in the air horn to allow fuel to be smoothly with-
drawn through the various systems (Fig. 6B-32).
Operation of WGD Low Speed or Idle System
Fuel is delivered to the engine through the low speed
system at closed throttle and light load speeds up to ap-
proximately 20 MPH. The low speed system also partially
controls fuel supply for light load speeds up to approxi-
mately 30 MPH.
The operation of the low speed system in each barrel of
the carburetor is identical. Fuel flows from the float cham-
ber through the metering rod jet into a passage which
supplies both the low speed jet and the main nozzle. It
'
then flows upward through the low speed jet which meters
the fuel used by the low speed system. At the upper end
of the low speed jet, the fuel is combined with a stream of
air comipg i n from the carburetor throat through a by-
pass. The combining of the air stream with the fuel tends
to atomize or break up the gasoline into a vapor (Fig.
6B-33).
Operation of each system of the WGD Carburetor carbu-
retor is described in the following sub-paragraphs.
-OAT
NEEDLE
-
AND
SEAT
Fig. 66-31 Carter WGD Carburetor Assembly
Fig. 88-32 Float System