Engine control system

A method of controlling the spark timing of an internal combustion engine having a shaft rotatably about an axis and means for generating a reference signal indicative of a reference shaft angular position and for generating signals indicative of incremental shaft angular positions, said method comprising the steps of selecting a first angular shaft position in relation to said reference shaft angular position and a later second angular shaft position both before the timing of the firing of the spark plug, selecting a fixed amount of shaft angular rotation, measuring the time said shaft requires to rotate through said selected fixed angular amount after the shaft reaches the first angular shaft position to determine an angular rotational speed for the shaft, computing the time required for the shaft to reach the timing of spark ignition from the second angular shaft position using the computed angular shaft rotational speed, and initiating firing after this time elapses.