To easily manufacture the fuel jet of a carburetor of which the throttle passage has length different corresponding to the flow rate of fuel.

Cylindrical parts 13 and 14 demarcating the outer diameter of the fuel jet are formed to the mating surface 27a of a mold 27 and a shaft- shaped third mold 19 demarcating the caliber of an outlet passage 9 is protruded into the inner end part of the cylindrical part 14 and an axial shaft hole 17a is provided to the axial center of the leading end of the third mold 19. A shaft- shaped fourth mold 15 is inserted in the through-hole 26 piercing the mold 25 mated with the mold 27 to be supported in the through-hole and the fourth mold 15 demarcating the caliber of an inlet passage 5 is protruded to the outer end part of the cylindrical part 13, and a small diameter shaft part 17, which demarcates the caliber of the throttle passage 17 formed to the leading end of the fourth mold 15, is fitted in the shaft hole 17a of the third mold 19 and the fourth mold 15 is axially moved to adjust the length of the throttle passage 7 of the fuel jet 2.