Abstract: A carburetor choke opening device wherein an altitude compensator opens an additional passage containing a delay element to vacuum at high altitudes so as to increase the amount of vacuum applied to the choke valve opening device at high altitudes, to insure that the choke valve continues to be opened without undue delay at high altitudes.

Abstract: In an exhaust gas recirculation system for an internal combustion engine of the back pressure control type which provides, by a vacuum-operated control valve, a pressure chamber of substantially constant and nearly atmospheric pressure at a middle portion of an exhaust gas recirculation passage, a thermostatic control means is incorporated in a vacuum passage which supplies control vacuum to the vacuum-operated control valve so as to modify the vacuum conducted therethrough in accordance with the temperature of the engine so that a partial ratio of exhaust gas recirculation is effected in cold operation of the engine.