Chevrolet Light Duty Truck 1973, Service Manual

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6 M - 4 4 ENGINE FUEL
ROCHESTER CARBURETOR DIAGNOSIS - MODELS M, MV
POSSIBLE CAUSE
CORRECTIVE ACTION
Carburetor flooding (continued)
3. Check float needle and seat for proper seal. If a needle
and seat tester is not available, apply mouth suction to
the needle seat w ith needle installed. If the needle is
defective, replace w ith a factory matched set.
4. 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. If wetness appears on
surface or float feels heavy (Check w ith known good float),
replace the float assembly.
5. Adjust float. Use procedure A.
Problem:
e n g i n e s t a r t s a n d s t a l l s
Engine does not have enough fast idle speed when cold. Check and re-set the fast idle setting and fast idle cam.
Use procedure C and D.
Choke vacuum break unit is not adjusted to specification
or unit is defective.
1. Adjust vacuum break to specification.
Use procedure E or F.
2. If adjusted O.K., check the vacuum break fo r proper
operation as follows:
On the externally mounted vacuum break unit, connect
a piece o f hose to the nipple on the vacuum break unit
and apply suction by mouth or use tool J-23417 to
appiy vacuum. Plunger should move inward and hold
vacuum. If not, replace the unit.
On the integral vacuum break unit remove cover and visual­
ly check diaphragm and vacuum channel. If diaphragm is
leaking, replace.
NOTE: Always check the fast idle cam adjustment before
adjusting vacuum break unit. Use procedure D.
Choke coil rod out of adjustment. Adjust choke coil rod.
Use procedure H or I.
Choke valve and/or linkage sticking or binding.
1. Clean and align choke valve and linkage. Replace if
necessary.
2. Re-adjust if part replacement is necessary.
Use procedure D, E or F.
Idle speed setting
Adjust idle speed to specifications on decal in engine com­
partment.
Not enough fuel in carburetor. 1. Check fuel pump pressure and volume.
2. Check for partially plugged fuel inlet filter. Replace if
dirty.
3. Remove air horn and check float adjustments. Use
procedure A.
Carburetor flooding.
NOTE: Check by using procedure outlined under carbu­
retor flooding. Page 1.
1. Check float needle and seat fo r 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
needle is defective, replace w ith a factory matched set.
2. Check float fo r being loaded w ith fuel, bent float hanger
or binds in the float arm.
2
LIGHT DUTY TRUCK SERVICE MANUAL