GMC 1976 ZEO 6083 Maintenance Manual page 368

6M- 26
ENGINE FUEL SYSTEM
The accelerator control system is a cable type .
The pedal is mounted to a lever which is connected
to the cable above the pedal, under the dash . As the
pedal is depressed the lever moves back pulling the
cable and engaging a transmission down shift switch .
There is no adjustment on the pedal or lever, and it
is important that the cable assembly NOT be lu-
bricated .
The fuel pump rocker arm is held in constant
engagement with the eccentric on the camshaft by
the rocker arm spring . As the end of the rocker arm
which is in contact with the eccentric moves upward,
the fuel link pulls the fuel diaphragm downward .
The action of the diaphragm enlarges the fuel cham-
ber drawing fuel from the tank through the inlet
valve and into the fuel chamber.
The pump delivers fuel to the carburetor only
when the pressure in the outlet line is less than the
pressure maintained by the diaphragm spring .
Therefore, when the carburetor float needle valve
opens, the spring will expand to move the diaphragm
upward to force fuel past the outlet valve to the
carburetor. When the carburetor float needle valve
closes, the pump builds up pressure in the fuel cham-
ber until the diaphragm spring is again compressed .
The diaphragm will then remain stationary until
more fuel is required by the carburetor .
INSPECTION AND TEST
There are three tests that can be preformed to
evaluate the fuel pump without removing the pump
from the engine . It is important that the pump per-
forms properly using all three tests.
ACCELERATOR LINKAGE
FUEL PUMP
Fuel Flow Test
Figure 32-Accelerator Linkage
1 . Be sure there is gasoline in the tank .
2. Check for loose line connections. A leak at the
pressure side of the system (line from pump to carbu-
retor) will be indicated by dripping fuel . A leak in the
suction side of the system (line from gas tank to
pump) will not be apparent except in its effect of
reducing volume of fuel on the pressure side of the
system .
3 . Look for bends or kinks in lines or hoses which
will reduce flow . Check the fuel pump inlet hose
routing to be sure it is not bent or kinked .
a. Remove coil secondary wire from distribu-
tor and ground to block so that engine can be
cranked without starting .
b. Disconnect fuel line at the carburetor inlet
fitting. Install a rubber hose approximately 8-10"
long over the end of the fuel line .
c . Place suitable container at end of the hose
and crank engine a few revolutions.
NOTE : If little or no gasoline flows from open
end of line, then the fuel line is restricted, gas