PURPOSE: To restrict the fluctuation in the air fuel ratio of mixed gas to be supplied to the engine by supperssing the volume of excessive fuel overflowing from a secondary main nozzle, even if the operating conditions are drastically changed, thereby tilting the oil level to a greater extent.

CONSTITUTION: A duplex carbureter 1 is provided with a primary carbureter 2 and a secondary carbureter 3. A fuel inlet nozzle 12 and a primary jet 9 are installed on the buttom of a float chamber 4, and the nozzle 12 and the jet a are communicated to a secondary main nozzle 7 through a fuel channel 11 and a main well 8. A fuel inlet nozzle 3 is provided on the side wall of the float chamber 4 below the fuel level, and said float chamber is communicated to the fuel channel 11 through a secondary jet 10. If the oil level of the float chamber 4 is assumed to be Y-Y, the fuel level inclination center 14 is positioned at the center of the float chamber 4. When a car is turned to right, the fuel level is tilted in the direction of Z-Z at the angle of Q around the center of the inclination center 14. The fuel inlet nozzle 13 is installed in such a way that it is located on the line Z-Z which connects the inclination center 14 to a fuel outlet upper end 15 located above the fuel level by the height of H. Therefore, if the inclination exceeds the angle of θ, the fuel inlet nozzle 13 is exposed to air.