An engine that refuses to start or is difficult to start is very frustrating. More often than not, the problem is very minor and can be found with a simple and logical troubleshooting approach.

Engine fails to start: Perform the following spark test to determine if the ignition system is operating properly:
Remove one of the spark plugs, connect the spark plug wire and connector to spark plug and touch the spark plug base to a good ground such as the engine cylinder head. Position the spark plug so you can see the electrodes.

WARNING...Do not hold the spark plug, wire or connector or a serious electrical shock may result. If necessary, use a pair of insulated pliers to hold the spark plug or wire. The high voltage generated by the ignition system could produce serious or fatal shocks.

If the spark is good, check for one or more of the following possible malfunctions: Obstructed fuel line or fuel filter, leaking head gasket(s), low compression.
If the spark is not good, check for one or more of the following: Weak ignition coil(s), weak TCI module, loose electrical connections, dirty electrical connextions, loose or broken ignition coil ground wire, broken or shorted high tension lead to the spark plug.

Engine is difficult to start: check for one or more of the following possible malfunctions: Fouled spark plug(s), improperly adjusted choke, contaminated fuel system, improperly adjusted carburators, weak TCI module, weak ignition coil(s), poor compression,
Engine will not crank: check for one or more of the following possible malfunctions: blown fuse, discharged battery, defective starter motor, seized piston(s), seized crankshaft bearing, broken connecting rods, locked-up transmission or clutchassembly.

Engine Performance:

The possible causes for each malfunction are listed in a logical sequence and in order of probability: Engine will not idle: Carburator incorrectly adjusted, fouled or improperly gapped spark plug(s), leaking head gasket(s), obstructes fuel line or fuel shutoff valve, ignition timing incorrect, valve clearence incorrect.
Engine misses at high speed: Fouled or improperly gapped spark plugs, improper carburator main jet selection, ignition timing incorrect, weak ignition coil(s), obstructed fuel line or fuel shutoff valve, clogged jets in carburators.
Engine overheating: Incorrect carburator adjustement or jet selection, ignition timing incorrect, improper spark plug heat range, damage or blocked cooling fins.

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