PURPOSE: To make the suction resistance in a suction passage to each cylinder almost equal by differentiating the venturi diameter carbureters provided for respective cylinder according to the length of the suction passage.

CONSTITUTION: A carbureter body 6 is composed of a main carbureter 9 and the other carbureter 10 which are communicated to the respective cylinders. The carbureters 9 and 10 have respectively throttle valves 13 and 25 in linkage with a shaft 26. A control valve 12 is arranged in front of the valve 13 of the carbureter 9, while one end of a sub-suction passage 15 communicated to the proximity of a suction valve 5 is arranged between both the carbureters 12 and 13. The diameters D1 and D2 each corresponding to Venturi 7a and 8a of the respective carbureters 9 and 10 differ from each other. They are determined by the length of a suction passage 3 located at the rear of the carbureters 9 and 10. Accordingly, the difference in the suction resistance between the carbureters 9 and 10 can be eliminated.