Variable venturi carburetor

A structure in a variable venturi carburetor of an internal combustion engine for preventing fuel vapor bubbles to pass to a main fuel jet comprising:

• a venturi portion, a float chamber, a main fuel passage communicating with the venturi portion and with the float chamber, the main fuel jet provided in the main fuel passage and a movable metering needle, a free end of said metering needle being adapted to control the size of the main fuel jet and a base portion of said metering needle being mounted to a suction piston adapted to transversely move with respect to the venturi portion in response to the condition of load on the internal combustion engine, an improvement including provision of a bypass detouring upwardly from a portion of the main fuel passage upstream of the main fuel jet for discharging the vapor of fuel, said bypass communicating with a negative pressure passage having an opening in a lower portion of said venturi portion and said bypass communicating also with an air passage having an opening in the vicinity of an air horn inlet.