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Chapter 13 Preventive Maintenance and Troubleshooting
Figure 13-31.
Typical troubleshooting chart for small gas engines.
Engine Troubleshooting Chart
Cause Remedy
Engine fails to start or starts with diffi culty
No fuel in tank. Fill tank with clean, fresh fuel.
Shut-off valve closed. Open valve.
Obstructed fuel line. Clean fuel screen and line. If necessary, remove and
clean carburetor.
Tank cap vent obstructed. Open vent in fuel tank cap.
Water in fuel. Drain tank. Clean carburetor and fuel lines. Dry spark
plug and points. Fill tank with clean, fresh fuel.
Engine overchoked. Close fuel shut-off and pull starter until engine starts.
Reopen fuel shut-off for normal fuel fl ow.
Improper carburetor adjustment. Adjust carburetor.
Loose or defective magneto wiring. Check magneto wiring for shorts or grounds; repair if
necessary.
Faulty magneto. Check timing, point gap; if necessary, overhaul magneto.
Spark plug fouled. Clean and re-gap spark plug.
Spark plug porcelain cracked. Replace spark plug.
Poor compression. Overhaul engine.
No spark at plug. Disconnect ignition cut-off wire at the engine. Crank engine.
If spark at spark plug, ignition switch, or safety switch
interlock switch is inoperative. If no spark, check magneto.
Crankcase seals and/or gaskets leaking (two cycle only). Replace seals and/or gaskets.
Exhaust ports plugged (two cycle only). Clean exhaust ports.
Engine knocks
Carbon in combustion chamber. Remove cylinder head and clean carbon from head
and piston.
Loose or worn connecting rod. Replace connecting rod.
Loose fl ywheel. Check fl ywheel key and keyway; replace parts if
necessary. Tighten fl ywheel nut to proper torque.
Worn cylinder. Replace cylinder.
Improper magneto timing. Time magneto.
Engine misses under load
Spark plug fouled. Clean and regap spark plug.
Spark plug porcelain cracked. Replace spark plug.
Improper spark plug gap. Re-gap spark plug.
Pitted magneto breaker points. Replace pitted breaker points.
Magneto breaker arm sluggish. Clean and lubricate breaker point arm.
Faulty condenser. Check condenser on a tester; replace if defective.
Improper carburetor adjustment. Adjust carburetor.
Improper valve clearance. Adjust valve clearance to recommended specifi cations.
Weak valve spring. Replace valve spring.
Reed fouled or sluggish (two cycle only). Clean or replace reed.
Crankcase seals leak (two cycle only). Replace worn crankcase seals.
(Continued)