To troubleshoot a motorcycle, first identify the exact problem, such as the engine not starting, the engine running poorly at low speed or the engine overheating. The engine may also be overcooling.
If the engine doesn't start at all, check the starter motor and the neutral switch for fault. Additionally, inspect the wiring for open ends or signs of short-circuiting. If none of these components are faulty, check whether the main fuse is blown. If the starter engine rotates but the engine doesn't turn over, inspect the starter motor clutch.
If the engine runs poorly at low speed, the spark produced by the spark plug could be weak. Check whether the spark plug is broken, dirty or incorrectly inserted. The cause could also be incorrect mixing of fuel and air. Check whether the pilot screw is correctly adjusted. Next, check for clogging in the pilot jet or the air passage. Ensure that the fuel level in the carburetor float bowl isn't too high or too low.
If the engine overheats, check whether the engine oil's level is too low. If it's at the proper level, the oil could be of poor quality. If the engine overcools, inspect the thermostatic fan switch. If the fan switch isn't faulty, inspect the thermostat.