PURPOSE: To improve the response under low speed region and the output under high speed region by arranging a high speed Venturi at higher position than a low speed Venturi while projecting the fuel nozzle of high speed Venturi into the Venturi from below.

CONSTITUTION: Low and high speed Venturis 1, 2 are juxtaposed in front and rear while coupling the outputs to the intake tube of single engine. Here, the high speed Venturi 2 is arranged at higher position than the low speed Venturi 1. Respective Venturi 1, 2 is opened/closed by sliding respective tubular throttle valve 3 up and down. The fuel nozzle 4 of low speed Venturi 1 is opened to be slightly exposed in the Venturi 1 while the fuel nozzle 5 of high speed Venturi 2 is projected into the Venturi 2 and opened at high position. Consequently, it can be operated with high response under low speed region while high output can be obtained under intermediate/high speed region.