Motorcycles use a coil and a magneto to time the engines ignition pulses. When this coil fails the engine behaves as if you have a bad plug. The engine may try to run on one cylinder or not at all. It is recommended that you first check the coil for 200 ohm resistance. A separated coil will be a dead give away but it is possible the coil only fails under load. That is a bit more difficult to measure. Crankcase gasket is included.