To prevent occurrence of excessive rich state of air-fuel mixture through sensitiveness of an acceleration pump even when a driver snap-operates a throttle valve lever.
Inside a body 16 of this evaporator, a cam is formed on a throttle valve shaft 26 of a cutout surface and a bearing surface. A cylinder chamber is formed perpendicularly to the throttle valve shaft 26. A piston holding a ball 32 and en energizing means are fitted to the cylinder chamber to compose an acceleration pump D. Fuel inside a constant pressure fuel chamber 54 is suctioned into the cylinder chamber by means of piston at the time of deceleration of the throttle valve shaft 26. The fuel in the cylinder chamber is fed to an intake passage 24 by means of the piston at the time of acceleration of the throttle valve shaft 26. A center axis of the cylinder chamber is eccentrically formed in respect to an axis of the throttle valve shaft 26. A contact of the ball 32 to the cam is moved to an axial peripheral surface from one side of the cutout surface through the center.
ENDO MASATOSHI
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