Abstract: A system for controlling the timing of an internal combustion engine having a rotatable power shaft including a timing mechanism coupled to an advance mechanism which produces a recurring ignition pulse. The timing mechanism produces a timing signal that recurs at a timing rate proportional to the rotational speed of the power shaft. The ignition pulse, which is initiated by the timing signal to establish the degree of spark advancement, is varied in response to an engine operating parameter, such as engine temperature to control spark advancement, and thereby reduce exhaust emissions.