Abstract: A fuel injection system for an internal combustion engine comprises at least one fuel injection valve for supplying fuel into the intake passage of the engine, an electronic control unit responsive to operating conditions of the engine for controlling a time period over which the fuel injection valve is opened and timing for opening the fuel injection valve, a generator responsive to rotation of a flywheel for generating electric power, the generator being connected to an ignition device and the electronic control unit and forming power supplies for driving the ignition device and the electronic control unit, a fuel pump arranged to be driven in unison with the flywheel by torque transmitted from the flywheel, and a pressure regulator for controlling pressure of fuel supplied from the fuel pump to the fuel injection valve.