Abstract: An engine synchronizer for synchronizing the speed of a slave engine with the speed of a master engine is disclosed. The disclosed synchronizer includes a comparison and control circuit deriving input signals from the distributors of two engines, e.g., the two engines of a power boat, one engine being arbitrarily designated the master engine and the other being arbitrarily designated the slave engine. The throttle of each engine is coupled to its associated hand throttle lever by means of a Bowden cable. One end of the sheath of the slave engine throttle control cable is attached to a slidable bracket. The slidable bracket is positioned within its limits of sliding movement by a positioning motor operating through a rack and pinion. Power to energize the positioning motor is supplied by the comparison and control circuit.