3.47
ENGINE
3
Engine Idles But Will Not Rev Up
• Spark plug fouled/weak spark
• Broken throttle cable
• Obstruction in air intake
• Air box removed (reinstall all intake components)
• Incorrect or restricted carburetor jetting
• ETC switch limiting speed
• Reverse speed limiter limiting speed
• Carburetor vacuum slide sticking/diaphragm damaged
• Incorrect ignition timing
• Restricted exhaust system
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
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