PURPOSE:To enable mounting of a carburetor unit without deceasing suction efficiency, by a method wherein an intake air pipe is extended in a direction, in which it is separated away from a crank shaft, along the central line of an included angle of bank. CONSTITUTION:An intake air pipe 37, communicated to an intake air port 25 and formed integrally with a cylinder head 15, is situated to inner side surfaces of two banks 2a and 2b, positioned facing each other, and extended along the central line of an included angle of bank in a direction extending at right angles with a crank shaft. The intake air pipe 37, extended from the two banks 2a and 2b, is formed such that axes A1 and A2 of the openings of the intake air pipe are positioned in parallel to each other, and end surfaces 38a in an axial direction of two open ends 38 are positioned flush with each other. A carburetor unit 38 is coupled to the two opening ends 38 through a joint member 39 formed by a rubber material and additionally serving as an insulator.
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