GMC 1976 ZEO 6083 Maintenance Manual page 355

ENGINE FUEL SYSTEM
6M- 13
POOR FUEL ECONOMY
Possible Cause Corrective Action
Power system in carburetor not
Free up or replace as necessary.
functioning properly .
Power piston sticking .
Vacuum leakage. It is absolutely necessary that all vacuum hoses
and gaskets are properly installed with no air
leaks. The carburetor and manifold should be evenly
tightened to specified torque . Carburetor to
manifold (to 15 ft. lbs.) .
Secondary throttle valves stick-
Loosen secondary throttle valve screws . Align
ing open or not seating properly .
valves in carburetor bores and tighten securely .
Possible Cause
Corrective Action
Engine needs complete tune
up .
Check engine compression, examine spark plugs, (if
dirty or improperly gapped, clean and re-gap or
replace), ignition point dwell, condition, re-adjust
ignition points if necessary and check and reset
ignition timing . Clean or replace air cleaner
element if dirty. Check for restricted exhaust
system and intake manifold for leakage. Make sure
all vacuum hoses are connected correctly.
Choke valve not fully opening.
1 . Clean choke and free-up linkage.
2. Check choke coil for proper adjustment.
Fuel leaks. Check fuel tank, fuel lines and fuel pump for any
fuel leakage.
High fuel level in carburetor or 1 . Check for dirt in the needle and seat . Test
carburetor flooding . using suction by mouth or needle seat tester .
2. Check for loaded float.
3 . Re-set carburetor float.
4. If excessive dirt is present in the carburetor
bowl, the carburetor should be cleaned.
Power system in carburetor not
Free-up or replace as necessary.
functioning properly .
Power piston sticking in up
position .
Metering rods bent or incorrect Clean or replace as necessary.
part . Main metering jets,
defective, loose or incorrect part
Fuel being pulled from accelera- Run engine at RPM where nozzles are feeding fuel .
for system into venturi through Observe pump jets . If fuel is feeding from jets,
pump jets . check pump discharge ball for proper seating by
filling cavity above ball with fuel to level of
casting. No "leak down" should occur with discharge
ball in place, Re-stake or replace leaking check ball .
Air bleeds or fuel passages in
Clean carburetor or overhaul as necessary.
carburetor dirty or plugged .