To properly adjust idle fuel flow in a carburetor without requiring high machining accuracy for a nozzle hole and the like, in the carburetor controlling fuel flow through the adjustment of the open area of the nozzle hole such that a metering needle operating in conjunction with a throttle valve is inserted into a pipe-shaped fuel nozzle whose nozzle hole is provided in a circumferential sidewall.

A tapering throttle part 36, which is formed at the tip of the narrow shank 35 of the metering needle 32 inserted in a through hole 12 in a fuel nozzle 11 with the nozzle hole 14 provided in the circumferential wall, is inserted into a metering hole 22 at the tip of a fuel adjusting member 16 and the longitudinal position of the fuel adjusting member 16 is adjusted to vary the end open area of the metering hole 22 at an idle position whereby the idle fuel flow delivered from a constant fuel chamber 8 to an intake passage 2 is adjusted.