These procedures assume the kickstarter cranks the engine over normally.
1. Engine misses erratically at all speeds — Intermittent trouble like this can be difficult to find. The fault could be in she ignition system, exhaust system (exhaust restriction), or fuel system. Follow troubleshooting procedures for these systems carefully to isolate the trouble.
2. Engine misses at idle only — Trouble could exist anywhere in ignition system. Trouble could exist in the carburetor idle circuits.
3. Engine misses at high speed only—Trouble could exist in the fuel system or ignition system. Check the fuel lines, etc. as described under Fuel System troubleshooting. Also check spark plugs and wires.
4. Poor performance at all speeds, lack of acceleration — Trouble usually exists in ignition or fuel system. Check each with the appropriate troubleshooting procedure.
5. Excessive fuel consumption — This can be caused by a wide variety of seemingly unrelated factors. Check for clutch slippage, brake drag, and defective wheel bearings. Check ignition and fuel systems.
1. Knocking or pinging during acceleration —Caused by using a lower octane fuel than recommended. May also be caused by poor fuel available at some “discount” gasoline stations. Pinging can also be caused by spark plugs of the wrong heat range.
2. Slapping or rattling noises at low speed or during acceleration — May be caused by piston slap, i.e., excessive piston-cylinder wall clearance.
3. Knocking or rapping while decelerating —Usually caused by excessive rod bearing clearance.
4. Persistent knocking and vibration — Usually caused by excessive main bearing clearance.
5. Rapid on-off squeal — Compression leak around cylinder head gasket or spark plugs.
This can be difficult to find without disassembling the engine. Usually this is caused by loose engine mounting hardware or worn engine or transmission bearings.
Fuel system troubles must be isolated to the carburetor, fuel tank, fuel tap, or fuel lines. These procedures assume that the ignition system has been checked and properly adjusted.
1. Engine will not start — First determine that the fuel is being delivered to the carburetor. Turn the fuel tap to the OFF position; remove the flexible fuel line to the carburetor. Place the loose end into a small container; turn she fuel tap to the ON or RESERVE position. Fuel should run out of the tube. If it does not, remove fuel tap and check for restrictions within it or the fuel tank.
2. Rough idle or engine miss with frequent stalling — Check carburetor adjustment.
3. Stumbling when accelerating from idle — Check idle speed adjustment.
4. Engine misses at high speed or lacks power — This indicates possible fuel starvation. Clean main jets and float needle valves.
5. Black exhaust smoke — Black exhaust smoke means a badly overrich mixture. Check that manual choke disengages. Check idle speed. Check for leaky floats or worn needle valves. Also check that jets are proper size.