GMC 4000 Series Service Manual page 295

Sec. 6A
Page 284
GASOLINE ENGINES
SYMPTOM D - IGNITION TROUBLES (Cont'd.)
POSSIBLE CAUSES
6.* Defective ignition coil or condenser.
7. Cracked distributor cap.
SYMPTOM A - POOR COMPRESSION
POSSIBLE CAUSES
1. Incorrect valve lash.
2. Leaky valves.
3. Valves or lifters sticking.
4.
W eak or broken v a lv e sp r in g s.
5. Valve timing incorrect.
6. Blown cylinder head gasket.
7. Broken or stuck piston rings.
8. Worn pistons, ring, and/or cylinder bores.
SYMPTOM B - IGNITION SYSTEM MALFUNCTION
POSSIBLE CAUSES
1. Ignition out of tim e.
2. Defective spark plugs.
3. Distributor points worn or out of adjustment.
SYMPTOM C - LACK OF FUEL
POSSIBLE CAUSES
1. Dirt or water in carburetor.
2. Gas lines partly clogged.
3. Dirt in gas tank.
4. Air leaks in gas line.
5. Fuel pump not functioning properly.
6. Governor malfunction.
SYMPTOM D - EXCESSIVE FUEL (FLOODING)
POSSIBLE CAUSES
1. Choke not fully open.
2. Air cleaner restricted.
3. Carburetor float valve not seating.
4. Rich mixture at idle speed.
G M C S E R V I C E M A N U A L
HARD STARTING (CONT.)
6. Test coil and condenser; replace if necessary.
7. Install new cap.
LACK OF POWER
1. Adjust to correct clearance.
2. Remove cylinder head and grind valves.
3. Free up or replace.
4.
5. Correct the valve timing.
6. Replace gasket.
7. Free up or replace piston rings.
8. Overhaul engine.
1. Set ignition timing.
2. Clean or replace spark plugs.
3. Clean and adjust points or replace.
1. Clean carburetor.
2. Clean gas lines.
3. Clean gas tank.
4. Tighten and check gas lines.
5. Replace or repair fuel pump.
6. Repair or replace governor.
1. Check choke and adjust control.
2. Service air cleaner.
3. Clean float valve and set float level.
4. Adjust carburetor idle mixture.
REMEDY
REMEDY
R ep lace d e fe c tiv e sp r in g s.
REMEDY
REMEDY
REMEDY