US Patent 7136742 Engine kill-switch control circuit and method of operating the same

A kill-switch control circuit for use with a light-duty combustion engine determines whether to execute a controlled shut down method or an immediate shut down method in response to kill-switch activation. The selection of a shut down method is made, at least in part, by using engine speed readings and by counting engine revolutions. The controlled shut down method utilizes ignition timing delay and/or spark ratio techniques to quickly bring the engine to a stop, yet does so in a controlled manner that avoids backfiring and other undesirable effects. Conversely, the immediate shut down method abruptly stops sending a current to the spark plug.