Chevrolet Light Duty Truck 1973, Service Manual

Page: 486 / 979

6 M - 6 2 ENGINE FUEL
ROCHESTER CARBURETOR DIAGNOSIS - ALL MODELS 4M, 4MV - FOUR BARREL
Problem:
N O P O W E R O N H E A V Y A C C E L E R A T I O N
O R A T H IG H S P E E D ( C O N T ' D )
POSSIBLE CAUSE
CORRECTIVE ACTION
Power system not operating,
(continued)
remove the carburetor air horn and check power piston
and cavity for d irt or scores. Check power piston spring
for distortion.
Float level too low.
Check and reset float level to specification.
Use procedure A.
Float not dropping far enough in bowl.
Check for bind in float hanger and float arm, float align­
ment in bowl and needle pull clip for sufficient clearance
on float arm.
Main metering jets or metering rods d irty, plugged or in­
correct part.
1. If the main metering jets are plugged or d irty or exces­
sive d irt is in fuel bowl, the carburetor should be com­
pletely disassembled and cleaned.
2. If the jets or rods are incorrect size, consult the parts
list for proper usage. The last two digits stamped on the
primary rods and jets are the last tw o digits o f the part
number. See identification chart J.
Problem :
E N G I N E S T A R T S H A R D
W H E N H O T
Choke valve not opening completely.
1. Check fo r binding choke valve and/or linkage. Clean
and/or replace as necessary.
Do not oil choke linkage.
2. Check and adjust choke thermostatic coil.
Use procedure G.
Engine flooded, carburetor flooding.
See procedure under "Engine cranks, w ill not start -
engine flooded."
No fuel in carburetor.
1. Check fuel pump. Run pressure and volume test.
2. Check float needle for sticking in seat, or binding float.
3. Check and adjust float level. Use procedure A.
Leaking float bowl.
Fill bowl w ith fuel and look for leaks.
Problem
E N G I N E R U N S U N E V E N O R S U R G E S .
Fuel restriction.
Check all hoses and fuel lines for bends, kinks or leaks.
Straighten and secure in position.
Check all fuel filters, if plugged or d irty - replace.
Dirt or water in fuel system.
Clean fuel tank, lines and filters.
Remove and clean carburetor.
Fuel level. Adjust float. Use procedure A.
Check for free float and float needle valve operation. Free
up or replace as necessary.
Metering rods bent or incorrect part. Main metering jets
d irty , defective, loose or incorrect part.
Clean or replace as necessary. See identification chart J.
Power system in carburetor not functioning properly.
Power piston sticking.
Free up or replace as necessary.
Vacuum leakage. It is absolutely necessary that all vacuum hoses and gaskets
are properly installed w ith no air leaks. The carburetor and
manifold should be evenly tightened to specified torque.
Carburetor to manifold (10-14 ft. lbs.).
5
LIGHT DUTY TRUCK SERVICE MANUAL