PURPOSE: To improve the response of the air-fuel ratio control by opening the sub-fuel path into the throttle bore independently from the main fuel path.

CONSTITUTION: A sub-fuel path 9 conducting to the fuel jet port 8 provided at the downstream of a throttle valve 7 is provided independently in a float chamber 2 while an actuator 10 is provided at the fuel jet port 8. The rich-lean signal of the air-fuel ratio from a computer 12 is fed as the operating signal for the actuator 10 which will function on said signal to correct the air-fuel ratio. The computer 14 will control the electrical output to the fuel jet port 8 through the engine temperature and to heat the fuel jet port 3.