Rochester 4Mv Quadrajet Carburetor; Rochester 4Mv Carburetor - Pontiac Grand Prix Service Manual

6B-20 1969 PONTIAC SERVICE MANUAL
closed
,
pull upward on the choke coil rod to the limit
of its wavela ~h~ end of the rod should fit the guage
The idle mixture should be adjusted to give a smooth
notch on the choke lever.
idle at the specified idle speed. Missing is a sign of too
lean an idle mixture while rolling or loping indicates
To adjust, Bend rod as shown.
ROCHESTER 4MV QUADRAJET
CARBURETOR
CARBURETOR ENGINE AND
MODEL TRANSMISSION
NUMBER USAGE
7029260
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
250A.T.
7029261
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
250
M.T.
7029262
. . . . . . . . . . . . . . . . . . . . . . . . .
428
Bonneville A.T.
7029263
. . . . . . . . . . . . . . . . . . . . . . . .
350-400 & 428
M.T.
7029268.
. . . . . . . . . . . . . . . . . . . . . . .
.350-400 & 428
A.T.
7029270.
. . . . . . . . . . . . . . . . . . . . . .
,400 Ram Air IV A.T.
7029273.
. . . . . . . . . . . . . . . . . . . . . .
,400 Ram Air
IV
M.T.
7028270
. . . . . . . . . . . . . . . . . . . . . . . . . .
400
Ram AirA.T.
7028273.
. . . . . . . . . . . . . . . . . . . . . . . .
.400
Ram Air M.T.
Carburetor identification and change code is stamped on
the throttle lever side of the float bowl.
ADJUSTMENTS ON CAR
All Rochester 4MV adjustments can be performed on
the car. With the exception of the idle speed and
mixture adjustment and the unloader adjustment, all
adjustments are included in the OVERHAUL AND
ADJUSTMENTS procedure.
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too rich a mixture. Turning the a l e mixture screw in
leans out the mixture; five turns out from the lightly
seated position may be used as a preliminary setting of
the mixture screws on six-cylinder engine, and six turns
out on V-8 engines. The mixture is to be' leaned out
from this initial setting to achieve the best lean idle.
PERIODIC SERVICE
ROCHESTER 4MV CARBURETOR
There are no periodic services required on the
Rochester 4MV carburetor; however, choke linkage,
choke valve and levers and pump linkage should be
kept free of dirt and gum so that they will operate
freely. DO NOT OIL LINKAGE.
OVERHAUL AND ADJUSTMENT
Flooding, stumble on acceleration and other perform-
ance complaints are, in many instances, caused by the
presence of dirt, water or other foreign matter. in the
carburetor. To aid in diagnosing the cause of the
complaint, the carburetor should be carefully removed
from the engine without draining rhe fuel from the
bowl. The contents of the fuel bowl may then be
examined for contamination as the carburetor is
disassembled.
The following is a step-by-step sequence by which the
Rochester 4MV carburetor may be completely disas-
sembled and reassembled. Adjustments may be made
and various parts of the carburetor may be serviced
without completely disassembling the entire unit.
NOTE: Place carburetor on proper holding fixture (Fig.
6B-47).