Engine Turns Over But Fails to Start

• No fuel

• Dirt in fuel line or filter

• Fuel will not pass through fuel valve

• Fuel pump inoperative/restricted

• Tank vent plugged

• Carb starter circuit

• Engine flooded

• Low compression (high cylinder leakage)

• No spark (Spark plug fouled)

Engine Does Not Turn Over

• Dead battery

• Starter motor does not turn

• Engine seized, rusted, or mechanical failure

Engine Runs But Will Not Idle

• Restricted carburetor pilot system

• Carburetor misadjusted

• Choke not adjusted properly

• Low compression

• Crankcase breather restricted

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 valves, 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

Spark Plug Fouling

• Spark plug cap loose or faulty

• Choke cable adjustment or plunger/cable sticking

• Foreign material on choke plunger seat or plunger

• Incorrect spark plug heat range or gap

• Carburetor inlet needle and seat worn

• Jet needle and/or needle jet worn or improperly adjusted

• Excessive carburetor vibration (loose or missing needle jet locating pins)

• Loose jets in carburetor or calibration incorrect for altitude/temperature

• Incorrect float level setting

• PVT system calibrated incorrectly or components worn or mis-adjusted

• Fuel quality poor (old) or octane too high

• Low compression

• Restricted exhaust

• Weak ignition (loose coil ground, faulty coil, stator, or ETC switch)

• ETC switch mis-adjusted

• Restricted air filter (main or pre-cleaner)

• Improperly assembled air intake system

• Restricted engine breather system

• Oil contaminated with fuel

• Restricted oil tank vent

Cooling Troubleshooting 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, or fuel pump)

• Fuel pump output weak

• Restricted radiator (internally or cooling fins)

• Water pump failure

• Cooling system restriction

• Cooling fan inoperative or turning too slowly

• Ignition timing misadjusted

• Low oil level

• Spark plug incorrect heat range

• Faulty hot light circuit

• Thermostat stuck closed or not opening completely

• Radiator is missing its internal diverter plate not allowing coolant to flow through entire radiator.

Temperature Too Low

• Thermostat stuck open

• Faulty water pump mechanical seal (coolant leak)

• Faulty pump shaft oil seal (oil leak)