To stably warm up an engine and operate the engine at a desired engine speed by supplying the proper amount of fuel at the start of the engine or in a specific speed range.

A first fuel system F1 is provided in which fuel in a constant fuel chamber 18 is fed to an intake passage 2 as it is metered with a metering needle 32 operating in conjunction with a throttle valve 5. A second fuel system F2 is provided in which the fuel pressurized by a fuel pump 8 is fed to the intake passage 2 under control of an electromagnetically driven control valve 52. The pressurized fuel under control of the control valve 52 is supplied to control engine speed, either at the start or warm-up of the engine or in the specific speed range, to maintain the desired engine speed.