PURPOSE: To successively open carburetor throttle valves in plural engines and obtain a desired output characteristic further improve fuel consumption, by providing a simple mechanism which comprises a movable pulley and cable wound on said pulley to alternatively perform continuous motion.

CONSTITUTION: The rotary center shaft of a shiftable moving pulley 15 is connected to a single of accelerator pedal 8, and a cable wound on this pulley 15 actuates to open throttle valves 7, 7' of two carburetors 6, 6' through a mechanism 9 of alternatively performing continuous motion. A difference is provided between spring tensions of return springs 20, 20' of the throttle valves. The accelerator pedal 8 is depressed to open the valve 7, if fully opened, the valve 7' begins to open. In this way, in a wide operational range spread from a low load to a high load, fuel consumption and/or operational performance can be always improved.