Bendix-Stromberg Carburetors - GMC 4000 Series Service Manual

CARBURETOR INSTALLATION
1. Be certain throttle body and intake manifold
sealing surfaces are clean.
2. Install new carburetor to manifold flange
gasket (if required).
3. Install carburetor over manifold studs.
Carburetors described in this section are used
on vehicles equipped with V -6 engines. The Bendix-
Stromberg (WW) carburetor (fig. 21) is used on
305C, 305E, and 351C engines. The Bendix-Strom-
berg (WWC) carburetor (fig. 22) is used on the
351M engine.
Both carburetors are of the down-draft double
barrel type. Each barrel of the carburetor has its
own idle system , main metering system and throttle
valve. The idle and main metering system s are
supplemented by the float system , the accelerating
system , and the power system .
The WW and WWC carburetors are equipped
with manual choke control. The choke lever is con­
nected to the throttle linkage to provide fast idle
speed position during the choke period.
IMPORTANT: For description of carburetor
operation and internal adjusting procedures refer
to Unit Overhaul Manual X-6M-03.
IDENTIFICATION
Each carburetor has an identification part
number tag on the air horn cover, next to the fue]
inlet, as shown in figure 21 and22. Before attempt­
ing to repair a carburetor, refer to the identifica­
tion number and secure the correct repair kit.
TROUBLE DIAGNOSIS
NOTE: The following information is included
to serve as a guide in servicing carburetor. Many
tim es a carburetor has been overhauled and re­
placed, yet the adverse condition still existed. Use
this information which may a ssist in isolating the
p recise problem.
Before condemning the carburetor as the
source of the engine running problem, always
FIRST check the following:
1. Ignition System - Are the points, condenser,
wires, spark plugs, and distributor operating to
specifications.
2. Valve lash and spark plug gap.
3. Engine compression.
4. Crankcase ventilation and Exhaust Emission
Control System (if used).
5. Fuel pump flow and pressure.
6. Intake manifold - cracks or gasket leakage.
G M C S E R V I C E M A N U A L

BENDIX-STROMBERG CARBURETORS

FUEL SYSTEM— GASOLINE ENGINES
4. Start vacuum and fuel lines at carburetor.
5. Install attaching nuts and tighten securely.
6. Tighten fuel and vacuum lines.
7. Connect and adjust accelerator linkage.
8. Connect choke tube or choke rod.
9. Make carburetor adjustments as outlined
previously under "Carburetor Adjustment."
7. Contaminate fuel.
8. Spark and valve timing.
9. Contaminated fuel filter.
When the carburetor is isolated to be the
source of the problem (above items all checked
snd are to specifications), Select one of the ten
complaints shown in "Troubleshooting Chart" that
best describes the problem, then proceed with the
action outlined.
CARBURETOR CHECKS
It is very seldom necessary to replace a com­
plete carburetor. They can generally be repaired
at a lower cost than the price of a new assembly.
Repair kits are readily available.
Although there may be exceptions, carburetors
should not be replaced for the following reasons:
-L Flooding - In practically all cases, flooding
is caused by a dirty or sticking float needle and
seat. This item is easily repaired and is not a
valid reason for replacing a carburetor.
2. Carburetor Spitback - Carburetors are not
to be replaced as a cure for "carburetor spitback."
This condition, in most cases, is not the fault of
the carburetor but results from inoperative p osi­
tive crankcase ventilation, incorrect valve lash, or
incorrect spark plug application and/or gap setting.
Spitback on acceleration may be caused by the
accelerator pump inlet ball check valve not prop­
erly seating. However, in no case should the car­
buretor be replaced to cure spitback.
3. Leaking - If leaking is due to a faulty car­
buretor, such as one with a porous casting, the
leak will show up at very early mileage (0-5,000
m iles). Low mileage leaking due to a porous hous­
ing is a valid reason for carburetor replacement
or repair, whichever is le ss costly. However, high­
er mileage leaking (over 5,000 miles) in most
cases is not caused by defective material in the
carburetor.
NOTE: Fuel seepage at the bowl to air horn
mating surface is normal. This usually shows up
as a discolored carburetor and is caused by wick-
ing of the gasket in the area. Correction involves
a periodic tightening of the bowl to air horn a s­
sembly screw s.
Sec. 6M
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