PURPOSE: To make an operating hole for a screw driver small in size so as to improve the strength of frames in a motorcycle equipped with four or more carburetors between right and left main frames by arranging the direction of drain holes of float chambers reciprocally.

CONSTITUTION: Carburetors 5aW5d are provided in line for respective cylinders between a right and a left frame 1 of a motorcycle. A drain 7 is provided to a float chamber 6 of respective carburetors, and its opening is covered with a screw type plug 8. The direction of respective drains is set so as to face each other reciprocally such that the drain 7 of the carburetor at the left end is directed to the left, and the drain 7 of the adjacent carburetor is directed to the right. And holes 9 are provided on a right and a left frame in order to operate the plug 8 to the drain of the right end and left end carburetors with a screw driver. As the frame 1 does not interfere the operation of the plug to the drain for two carburetors at the center, no hole is required to be made whereby the strength of the frame is improved.