GMC 4000 Series Service Manual page 341

Sec. 6M
Page 330
FUEL SYSTEM— GASOLINE ENGINES
BEN D HERE TO
'A"
ADJUST FLOAT
G A U G E FRO M
UP O R D O W N
TOP O F C A ST IN G
TO TOP O F
FLOAT AT TOE
Figure 19— Float Level Adjustment
6. Remove air horn by lifting straight up. In­
vert air horn and place on a clean bench. Remove
air horn to bowl gasket.
7. Hold float bowl retaining pin firmly in
place and lightly p ress down on very end of float
arm as shown in figure 19.
8. With adjustable T -scale, measure distance
from top of float at toe to float bowl gasket sur­
face (gasket removed). Measurement should be
made at point 1/16-inch from end of flat surface
at float toe (not on radius). Float level should be
%-inch.
9. Bend float pontoon up or down to adjust.
10. Install air horn gasket on float bowl by
G M C S E R V I C E M A N U A L
place.
HO LD FLOAT
R E T A IN IN G PIN
FIRMLY IN PLACE
throttle.
LIGHTLY PRESS D O W N
O N VERY EN D
O F FLO AT A R M
V
T-6049
carefully sliding slit portion of gasket over m eter­
ing rod holder. Then align gasket with dowels pro­
vided on top of bowl casting and p ress firmly in
NOTE: Before installing air horn, check oper­
ation of metering rod and accelerator pump to en­
sure free operation from closed to wide open
11. Install air horn to float bowl by lowering
gently on to float bowl until seated. Install three
long and three short air horn to float bowl attach­
ing screw s. Tighten screw s securely using correct
tightening sequence as shown in figure 20.
12. Assemble choke rod to choke shaft lever.
End of rod points away from air horn casting when
installed properly. (Lower end of rodhas 45-degree
bend.)
13. Install lower end of choke rod into curved
slot in fast idle cam. Part number on cam should
face outward.
14. Install fast idle cam to main body and
tighten retaining screw securely.
15. Connect manual choke wire to choke lever.
16. Install carburetor air cleaner.
CARBURETOR REPLACEMENT
CARBURETOR REMOVAL
Flooding, stumble on acceleration and other
performing complaints are, in many instances,
caused by the presence of dirt, water, or other
foreign matter in the carburetor. To aid in diag­
nosing the cause of the complaint, the carburetor
should be removed from the engine without drain­
ing the fuel from the bowl. The contents of the fuel
bowl may then be examined for contamination as
the carburetor is disassembled.
1. Remove air cleaner and gasket.
2. Disconnect fuel and vacuum lines from
carburetor.
3. Disconnect choke cable.
4. Disconnect accelerator linkage.
5. Remove carburetor attaching nuts and re­
move carburetor.
TEST BEFORE INSTALLATION
It is good shop practice to fill the carburetor
bowl before installing the carburetor. This reduces
the strain on the starting motor and battery and
reduces the possibility of backfiring while attempt­
ing to start the engine. A fuel pump clamped to the
bench, a small supply of fuel and the necessary
fittings enable the carburetor to be filled and the
operation of the float and intake needle and seat to
be checked. Operate the throttle several tim es and
check the discharge from the pump jets before in­
stalling the carburetor.