Pontiac tempest 1968 Service Manual page 332

E N G I N E FUEL
6 B - 2 5
OVERHAUL AND ADJUSTMENT
Flooding, stumble on acceleration and other per­
formance complaints are, in many instances, caused
by the presence of dirt, water or other foreign mat­
ter in the carburetor. To aid in diagnosing the cause
of the complaint, the carburetor should be carefully
removed from the engine without draining the 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
disassembled and reassembled. Adjustments may be
made and various parts of the carburetor may be
serviced without completely disassembling the entire
unit.
SECONDARY
METERING RODS
AIR VALVE
MAIN WELL AIR /
BLEED TUBES
SECONDARY v ' - AIR VALVE
ACCELERATING" TORSION
WELL TUBES • SPRING
SECONDARY
FUEL DISCHARGE
NOZZLES
Fig. 6B-59 Air Horn Assy.
NOTE: Place carburetor on proper holding fixture.
DISASSEMBLY
AIR HORN REMOVAL (Fig. 6B-58)
1. Remove idle vent valve attaching screw then
remove idle vent valve assembly.
2. Remove clip from upper end of choke rod, dis­
connect choke rod from upper choke shaft lever and
remove choke rod from bowl.
6. Remove nine air horn to bowl attaching screws
two attaching screws are located next to primary
venturi, (Four long screws, three short screws, two
counter-sunk screws).
7. Remove air horn by lifting straight up. Air
horn gasket should remain on bowl for removal
later.
CAUTION: Care must be taken not to bend two
small main well air bleed tubes protruding from
air horn. These are permanently pressed into
casting. DO NOT REMOVE.
3
0
Remove spring clip from upper end of pump rod
then disconnect pump rod from pump lever.
4. Disconnect clip from vacuum break rod and
remove rod.
5. Remove metering rods and hanger by removing
screw from metering rod hanger located between
air valves and lift out.
CHOKE VALVE
CHOKE RCD
AIR HORN SCREWS(9)
P U M P LEVER
•
i
PUMP RCD
/
-*' ~*
• *T'
IDLE S P E E D
S C R E W
\
F U E L I N L E T
Fig. 6B-58 Rochester 4 M V Carburetor
AIR HORN DISASSEMBLY (Fig. 6B-59)
NOTE: Disassembly of air horn is not required
for cleaning purposes. If part replacement is
required, proceed as follows:
1. Remove choke valve attaching screws then re­
move choke valve and shaft.
2. Remove pump lever roll pin then pump lever.
CAUTION: Air valves and air valve shaft should
not be removed.
FLOAT BOWL DISASSEMBLY (Fig. 6B-60)
1. Remove pump plunger from pump well.
2. Remove air horn gasket from dowels on second­
ary side of bowl, then remove gasket from around
power piston and primary metering rods.
3. Remove pump return spring from pump well.
4. Remove plastic filler over float valve.
5. Remove power piston and primary metering
rods, using needle nosed pliers to pull straight up on
metering rod hanger directly over power piston