Abstract: A carbutetor having an intake pass, an axially movable throttle valve, a main nozzle, a main jet fixedly disposed on the lower end of the main nozzle having an axial channel, a conical surface and a planar surface. The main jet comprises a plurality of downwardly directed oblique holes formed on the conical surface and extending to the axial channel. The surface of the oblique holes is made of a rough surface in order to reduce the boundary layer of fuel flowing through the oblique holes, thereby creating a smooth flow of fuel and improving fuel efficiency.