PURPOSE:To provide a carburetor having an acceleration pump, which is enabled to increase fuel supply at the low-speed region, by forming a fuel reservoir chamber communicated with a pump chamber for reserving fuel therein only when a piston of the acceleration pump is located within a prescribed distance from its waiting position. CONSTITUTION:A carburetor of an outboard engine of this invention comprises a main fuel system and a slow-speed system including by-pass ports 30, 31 and an idle port 29 which are opened in an intake passage 13 respectively on the upstream and downstream sides of the position where a throttle valve 15 is located when it is fully closed. Further, an acceleration pump 19 is provided in a subsidiary body 11B. In such an arrangement, a fuel reservoir chamber 34 is formed adjacently of a pump chamber 25 of the acceleration pump 19, and the chamber 34 is communicated with the pump chamber 25 via a connecting port 35. Further, a suction nozzle 36 is disposed in the reservoir chamber 34 in the manner that it is communicated via a fuel passage 37 with a subsidiary by-pass port 38 which is opened in the intake passage 13 slightly on the upstream side of the position where the throttle valve 15 is located when it is fully closed. The connecting port 35 is formed at such a position that it is kept open during the while when the throttle valve 15 is moved from its fully closed position to the position facing the port 38.
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