Chevrolet 70 Series 1970, Service Manual

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ROUGH IDLE AND/OR STALLING (CONT.)
GASOLINE ENGINES 6A-23
SYMPTOM A - ERRATIC RUNNING OR SURGING (Cont'd.)
POSSIBLE CAUSES
4. Inoperative crankcase ventilation v alves.
5. Cylinder head gask ets leaking, or cylinder head
cracked.
6. Worn valve guides.
REMEDY
4. Clean or rep lace v a lv es.
5. R eplace cylinder head or gasket.
6. Overhaul cylinder head.
SYMPTOM B - STALLING
POSSIBLE CAUSES
1. Engine idle speed set too slow .
2. Engine running too cool.
3. Exhaust restr ic ted .
4. Carburetor flooding.
5. D efective fuel pump.
REMEDY
1. Adjust idle speed to sp ecification s.
2. Install proper therm ostat.
3. Repair exhaust sy stem to elim inate e x c e ssiv e
back p r e ssu r e .
4. R eplace defective float valve, se t carburetor
float le v e l. Check fuel pump for e x c e ssiv e
p r e ssu r e .
5. R eplace pump.
DETONATION
(SPARK KNOCK OR PING ON ACCELERATION)
POSSIBLE CAUSES
1. Ignition advance too far for fuel being used.
2. Wrong type (heat range) spark plug.
3. E x ce ssiv e build-up of d ep osits in com bustion
cham bers.
4. R estricted coolant p a ssa g e s in cylinder head
causing "hot spots" in com bustion cham ber.
5. Overheated engine.
6. Lugging engine.
REMEDY
1. Retard ignition tim ing.
2. Install co rrect spark plug.
3. Clean com bustion cham bers.
4. Remove cylinder head and clean p a ssa g e s.
5. Make correctio n s to low er the engine operating
tem perature. (Refer to "Causes" and "Remedied'
previou sly covered under "Overheating.")
6. U se low er tra n sm issio n gear to prevent o v er­
loading engine.
HIGH LUBRICATING OIL CONSUMPTION
POSSIBLE CAUSES REMEDY
1. Oil lin e s or connections leaking. 1. Tighten or rep lace d efective p arts.
2. Leaking gask ets. 2. R eplace gask ets as n e c essa ry .
3. Crankcase oil le v e l too high.
3. Drain cran k case and r e fill to co rr ect le v e l.
4. Crankshaft oil s e a ls worn.
4. Replace oil s e a ls .
5. Pistons and/or rin gs worn, or pistons damaged;
cylinder bores scored or worn. 5. Overhaul engine.
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL