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3.54
ENGINE
Engine Has Low Power
• Spark plug fouled
• Cylinder, piston, ring, or valve wear or damage
(check compression)
• PVT not operating properly
• Restricted exhaust muffler
• Carburetor vacuum slide sticking/diaphragm
damaged
• Dirty carburetor
Piston Failure - Scoring
• Lack of lubrication
• Dirt entering engine through cracks in air filter or
ducts
• Engine oil dirty or contaminated
Excessive Smoke and Carbon Buildup
• Excessive piston-to-cylinder clearance
•Wet sumping
• Worn rings, piston, or cylinder
• Worn valve guides or seals
• Restricted breather
• Air filter dirty or contaminated
Low Compression
• Decompressor stuck
• Cylinder head gasket leak
• No valve clearance or incorrectly adjusted
• Cylinder or piston worn
• Piston rings worn, leaking, broken, or sticking
• Bent valve or stuck valve
• Valve spring broken or weak
• Valve not seating properly (bent or carbon
accumulated on sealing surface)
• Rocker arm sticking
Backfiring
• ETC or speed limiter system malfunction
• Fouled spark plug or incorrect plug or plug gap
• Carburetion faulty - lean condition
• Exhaust system air leaks
• Ignition system faulty:
Spark plug cap cracked/broken
Ignition coil faulty
Ignition or kill switch circuit faulty
Ignition timing incorrect
Sheared flywheel key
• Poor connections in ignition system
• System wiring wet
• Valve sticking
• Air leaks in intake
• Lean condition
Cooling System
Overheating
• Low coolant level
• Air in cooling system
• Wrong type of coolant
• Faulty pressure cap or system leaks
• Restricted system (mud or debris in radiator fins or
restriction to air flow, passages blocked in radiator,
lines, pump, or water jacket)
• Lean mixture (restricted jets, vents, fuel pump or
fuel valve)
• Fuel pump output weak
• Restricted radiator (internally or cooling fins)
• Water pump failure
• Cooling system restriction
• Cooling fan inoperative or turning too slowly
(perform current draw test)
• Ignition timing misadjusted
• Low oil level
• Spark plug incorrect heat range
• Faulty hot light circuit
• Thermostat stuck closed or not opening
completely
Temperature Too Low
• Thermostat stuck open
Leak at Water Pump Weep Hole
• Faulty water pump mechanical seal (coolant leak)
• Faulty pump shaft oil seal (oil leak)