Engine speed control system for outboard motor

A system for controlling a speed of an internal combustion engine of an outboard motor that is adapted to be mounted on a stern of a boat and having a propeller powered by the engine to produce thrust that propels the boat in a forward or reverse direction in response to a shift position established by a shift mechanism, comprising:

• a throttle actuator connected to a throttle valve of the engine to open and close the throttle valve;
• an operation device provided to be manipulated by an operator to input an instruction to regulate the speed of the engine in accordance with an amount of manipulation;
• a manipulation amount detector which detects the amount of manipulation of the operation device;
• a desired throttle opening determiner which determines a desired opening of the throttle valve based on the detected amount of manipulation of the operation device;
• an actuator controller which controls operation of the throttle actuator to make an opening of the throttle valve equal to the desired throttle opening;
• a desired engine speed determiner which determines a desired speed of the engine based on the desired throttle opening;
• an engine speed detector which detects the speed of the engine;
• and
• an overrev discriminator which compares the detected engine speed with the desired engine speed and discriminates that the engine overrevs when the detected engine speed is larger than the desired engine speed;
• wherein the actuator controller implements an overrev prevention control to operate the throttle actuator to decrease the opening of the throttle valve such that the detected engine speed is lowered to the desired engine speed, when the engine is discriminated to overrev.