A system and method for controlling an internal combustion engine and electrical inverter system for powering a load, including controlling the operation of a spark-ignited internal combustion engine prime mover used in generation of electrical power by way of a generator. A microprocessor (e.g., DSP) controlled circuit taking engine speed input from an engine speed signal is used to control the operation of the internal combustion engine prime mover so that it is preferably operated substantially at wide open throttle.