A device that corrects with ease and high precision any deviation of the fuel flow rate due to variation in the constituent components of a carburetor, and to improve the exhaust condition and operability of an engine. A carburetor in which the delivery channel 23 and the suction channel 20 of a fuel pump 15 are connected with the aid of an escape channel 27, and in which a portion of the delivery fuel is allowed to escape to the suction side in order to prevent pressure exerted on the fuel valve 10 by the fuel delivered to the constant fuel chamber 5 from the fuel pump 15, which operates by pressure pulses, from reaching or exceeding a specified level, wherein the escape channel 27 is equipped with a manual control valve 29 for steplessly adjusting the surface area thereof. The quantity of fuel retained in the constant fuel chamber 5 can be adjusted so as to achieve a predetermined fuel flow rate by changing the escape quantity of the delivery fuel and rendering the fuel valve 10 more resistant to opening or less resistant to opening.