Chevrolet Light Duty Truck 1973, Service Manual

Page: 470 / 979

6 M - 4 6 EN GINE FUEL
ROCHESTER CARBURETOR DIAGNOSIS MODELS M, MV
PO SSIBLE CAUSE C O R R E C T IV E ACTION
D irt in pump passages or pump jet. Clean and Blow out w ith compressed air.
Fuel level.
Check fo r sticking float needle or binding float. Free up
or replace parts as necessary. Check and reset float level
to specification. Use procedure A.
Leaking air horn to float bowl gasket.
Torque air horn to float bowl using proper tightening
procedure. Use procedure J.
Carburetor loose on manifold.
Torque carburetor to manifold bolts. (10-14 ft. lbs.).
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 I G H S P E E D
Carburetor th ro ttle valve not going wide open. (Check
by pushing accelerator pedal to floor).
Adjust th ro ttle linkage to obtain wide open thro ttle in
carburetor.
D irty or plugged fuel filters.
Replace w ith a new filte r element.
Power system not operating.
Check power piston fo r free up and down movement.
If power piston is sticking check power piston and cavity
for dirt, or scores. Check power piston spring for dis­
tortion. Clean or replace as necessary.
Metering rod not adjusted to specification.
Adjust metering rod. Use procedure B.
Float level too low.
1. Check and reset float level to specification. Use
procedure A.
Float not dropping far enough into float bowl.
Check fo r binding float hanger and fo r proper float align­
ment in float bowl.
Main metering jet or metering rod d irty , plugged or in­
correct part.
1. If the main metering jets are plugged or d irty and exces­
sive d irt is in the fuel bowl. The carburetor should be
completely disassembled and cleaned.
2. Check the jet or rod for being the correct part. Consult
the parts list for proper usage. The last tw o digits
stamped on the jet face are the same as the last two
digits of the part number. The metering jet and rod
can be identified using chart.
Use procedure K.
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 for binding choke valve and/or linkage. Clean
and free-up or replace parts as necessary.
Do not oil choke linkage.
2. Check and adjust choke thermostatic coil.
Use procedure FI or I.
Engine flooded - Carburetor flooding. See procedure under "Engine cranks, w ill not start” . Pg. 1
No fuel in carburetor. 1. Check fuel pump. Run pressure and volume test.
2. Check float needle fo r sticking in seat, or binding float.
Leaking float bowl. Fill bowl w ith fuel and look for leaks.
4
LIGHT DUTY TRUCK SERVICE MANUAL