Abstract: A speed control for an engine having a throttle and a drive shaft made up of a selective gear connected to a differential gear and a responsive gear connected to a second differential gear all rotatable about a common axis. Two differential pinions rotatably connected to the differential gears and supported on a pinion shaft disposed at right angles to the axis. The center of the pinion shaft being attached to a drum mounted concentric to the axis and having an actuating member connected from the drum to the engine throttle and a reference motor operatively connected to the first side gear to drive it at a selected speed and a drive shaft from the engine driving the second side gear.