Abstract: Disclosed herein is an internal combustion engine provided with an exhaust gas recirculation system of so-called back pressure control type. The exhaust gas recirculation system is provided with a vacuum line connecting a so-called EGR port with a vacuum operated flow control valve, and a modulator valve having a control chamber selectively opened to the vacuum line in response to the pressure of recirculated exhaust gas for controlling vacuum signal level of the flow control valve. The control chamber of the modulator is connected to another vacuum signal port located slightly above the EGR port.

Abstract: The apparatus according to the present invention includes means for conducting secondary air into the exhaust lines of a multi-cylinder internal combustion engine, which conducts the secondary air into exhaust passages for one or more of the cylinders, and means for conducting a requisite amount of atmospheric air into the intake lines of the all or a part of the cylinders being available for said secondary air conduction, in response to an abrupt change of the negative pressure in the intake pipe through a mixture control valve.