GMC 1976 ZEO 6083 Maintenance Manual page 273

6A- 8 ENGINE
ENGINE STALLS AT IDLE - ENGINE COLD (OK WHEN HOT)
CARBURETOR (3) (5)
Idle too low .
Choke high idle too low .
ENGINE STALLS AT IDLE - ENGINE HOT (OK WHEN COLD)
MECHANICAL
GENERAL
Vapor lock . (11)
Engine overheats. (Refer to "Engine
Overheats" in this section .)
Positive crankcase ventilation valve.
CARBURETOR (3) (4)
Idle set too low.
GENERAL
Check all vacuum hoses for proper routing,
broken or disconnected hoses and/or caps .
Also vacuum leaks. (9)
Restricted air cleaner (Remove air cleaner
with engine running and note engine rpm .) .
Incorrect timing and dwell.
Positive crankcase ventilation valve dirty
or stuck.
Restricted exhaust.
Cold engine (Faulty thermostat) .
Fuel volatility too high or low.
IGNITION (6)
Improper plug or plug gap.
Faulty plugs.
Improper point setting, worn or damaged.
Defective condenser and toil .
Faulty rotor or cap.
Loose wiring .
Damaged or corroded coil wiring or spark
plug cables .
Moisture on wiring or in distributor cap .
Cracked distributor cap.
ROUGH ENGINE IDLE (1)
MECHANICAL
Linkage improperly adjusted or damaged .
Throttle linkage improperly adjusted or
faulty .
FUEL
Engine idle speed improper .
Mixture too rich or lean . (4)
Float level .
Dirt and water in fuel system .
Carburetor mounting bolts loose.
MECHANICAL
Choke linkage, secondary throttle plates
sticking, binding or damaged . (3)
Low compression.
Valve train faulty (Burnt or sticky
valves, broken spring, bent push rod etc.) .
Loose engine mounts or worn insulation .
Improperly torqued cylinder head .
Leaking or worn valve guides .
NOTE: When repairs have been made it may be necessary to re-adjust idle speed.