PURPOSE: To improve the operability at idling time and reduce exhaust gas containing noxious components, in a multiple-cylinder 4-cycle engine, by a mechanism whereby the fuel injection time of each cylinder is synchronized with its stroke so that each cylinder injects fuel under the identical air pressure condition and that difference in exhaust gas composition between each cylinder is minimized.

CONSTITUTION: With the engine 14 started, the air stream let into the muffler chamber 16 is divided to flow into each throttle body 1 to mix with the fuel supplied from each fuel injection valve 3. The mixture is then supplied to the engine 14. The output signals from the hot wire air flow meter 6, the engine revolution sensor 8 and the temperature sensor 9 are fed into the control unit 7. This control unit 7 calculates valve opening time thereby making the rotary shafts synchronize with each other per revolution to open the fuel injection valves 3. The fuel injection time is when the pressure of inlet air against the fuel injection valves 3 becomes identical. The difference in pressure between before and after the fuel meter on the fuel injection valve 3 is the same with all of the fuel injection valves so that each of the fuel injection valves 3 supplies the same quantity of fuel proportional to valve opening time.