Chevrolet Light Duty Truck 1973 Service Manual page 469

ROCHESTER CARBURETOR DIAGNOSIS
POSSIBLE CAUSE
Carburetor flooding (continued)
P roblem :
Idle speed setting.
Manifold vacuum hoses disconnected or improperly in­
stalled.
Carburetor loose on intake manifold.
Intake manifold is loose or gaskets are defective.
Hot idle compensator not operating (where used.)
Carburetor flooding.
NOTE: Check by using procedure outlined under "carbu­
retor flooding" , page 1.
Problem:
Defective accelerator pump system
NOTE: A quick check of the pump system can be made as
follows. With the engine o ff, remove air cleaner and look
into the carburetor bores and observe pump stream, while
briskly opening throttle valve. A full stream of fuel should
emit from pump jet and strike near the center o f the
venturi area.
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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
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
MODELS M, MV
CORRECTIVE ACTION
NOTE: A solid float can be checked fo r fuel absorption
by lightly squeezing between fingers.
on surface or float feels heavy (check w ith known good
float, replace the float assembly.
3. Check float adjustments. Use procedure A.
4. If excessive d irt is found in the carburetor, clean the
fuel system and carburetor.
necessary.
Re-set idle speed per instructions on decal in engine
compartment.
Check all vacuum hoses leading into the manifold or
carburetor base fo r leaks or being disconnected.
or replace as necessary.
Torque carburetor to manifold bolts (10-14 ft. lbs.).
Using a pressure oil can, spray light oil or kerosene around
manifold legs and carburetor base. If engine RPM changes,
tighten or replace the manifold gaskets or carburetor base
gaskets as necessary.
Normally the hot idle compensator should be closed when
engine is running cold and open when engine is hot (approx.
140°F at comp.) replace if defective.
1. Remove air horn and check float adjustment.
procedure A.
2. 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.
3. Check float for being loaded w ith fuel, bent float hanger
or binds in the float arm.
NOTE: A solid float can be checked fo r fuel absorption by
lightly squeezing between fingers.
surface or float feels heavy (check w ith known good float),
replace the float assembly.
4. If excessive d irt is found in the carburetor, clean the
fuel system and carburetor.
necessary.
1. Remove air horn and check pump cup.
scored or distorted, replace the pump plunger.
2. Check the pump discharge ball fo r proper seating and
location. The pump discharge ball is located in a cavity
next to the pump well.
remove air horn and gasket and fill cavity w ith fuel. No
"leak dow n" should occur. Restake and replace check
ball if leaking. Make sure discharge ball, spring, and re­
tainer are properly installed.
3
E N G IN E FUEL 6 M - 4 5
If wetness appears
Replace fuel filters as
Install
Use
If wetness appears on
Replace fuel filters as
If cracked,
To check fo r proper seating,
LIGHT DUTY TRUCK SERVICE MANUAL