Chevrolet Light Duty Truck 1973, Service Manual

Page: 477 / 979

E N G IN E FUEL 6 M - 5 3
ROCHESTER CARBURETOR DIAGNOSIS - MODELS 2G, 2GV - TWO BARREL
Problem:
E N G I N E I D L E S R O U G H
A N D S T A L L S ( C O N T I N U E D )
POSSIBLE CAUSE CORRECTIVE ACTION
Carburetor flooding.
NOTE: Check by using procedure outlined under engine
flooded. See page 1.
Remove air horn and check float adjustments. Use pro­
cedure A and B or C and D.
If excessive d irt is found in the carburetor, clean the fuel
system and carburetor.
Replace fuel filters as necessary.
Check float needle and seat for proper seal. If a needle
and seat tester is not available, mouth suction can be
applied to the needle seat w ith needle installed. If the
needle is defective, replace w ith a factory matched set.
Check float for being loaded w ith fuel, bent float hanger
or binds in the float arm.
NOTE: A solid float can be checked for fuel absorption
by lightly squeezing between fingers. If wetness appears
on surface or float feels heavy (check w ith known good
float, replace the float assembly.
Check metal float for leakage by shaking.
Problem :
e n g i n e h e s i t a t e s o n a c c e l e r a t i o n
Accelerator pump not adjusted to specification. Adjust accelerator pump. Use procedure E.
Defective accelerator pump system.
Note: A quick check of the pump system can be made as
follows. With the engine o ff, look into the carburetor
bores, and observe pump shooters, while briskly opening
thro ttle valves. A full stream of fuel should emit from
each pump jet and squirt into the venturi area.
Remove air horn and check pump cup. If cracked, scored
or distorted, remove the pump plunger. Check the pump
discharge ball for proper seating and location. The pump
discharge ball is 3/16” steel and is located beneath the
venturi cluster assembly. Check pump discharge ball for
proper seating by filling cavity above ball w ith fuel to level
of casting. No "leak down” should occur w ith discharge
ball, spring and retainer in place. Re-stake or replace check
ball if leaking
D irt in pump passages. Clean and blow out w ith compressed air.
Float level.
Check for sticking float needle or binding float. Free up
or replace parts as necessary.
Check and reset float level and drop to specification.
Use procedure A and B or C and D.
Carburetor loose on manifold.
Torque carburetor to manifold bolts (10-14 ft. lbs.).
Problem :
N O PO W ER O N H E A V Y A C C E L E R A T I O N O R A T H I G H S P E E D
Carburetor th ro ttle valves not going wide open. (Check by
pushing accelerator pedal- to floor).
Adjust thro ttle linkage to obtain wide open thro ttle in
carburetor.
D irty or plugged fuel filters.
Replace w ith a new filte r element.
3
LIGHT DUTY TRUCK SERVICE MANUAL