Abstract: A device for controlling the air-fuel ratio of the mixture supplied to an internal combustion engine having a Venturi-type carburetor is disclosed. The device comprises a sensor for detecting the concentration of oxygen contained in the exhaust gas, an electromagnetic valve arranged in an air bleed passage of said carburetor, which passage is controlled so as to be either of opened or closed by said valve in accordance with a signal from said sensor, and another valve comprising an air valve arranged in said air bleed passage and controlling the quantity of air bleed by changing the opening area of said air bleed passage in accordance with the quantity of the suction air introduced to a combustion chamber.

Abstract: An air-fuel ratio control system in a twin carburetor type of an internal combustion engine comprising two SU carburetors each provided with an air-bleed passage opening into a main nozzle of said carburetor, a quantity of the bled air being regulated by an electromagnetic valve means which operates in response to an output signal emanating from a common oxygen sensor installed in the exhaust manifold, a phase difference being produced between input signals supplied to the two electromagnetic valve means, by a phase difference control unit.