In a system including a carburetor for regulating the air/fuel ratio fed to an internal combustion engine, a sensor is positioned in the exhaust pipe to provide a control signal indicating the amount of some exhaust gas constituent, such as oxygen. A control circuit is provided to regulate the position of a carburetor component, to change the air/fuel ratio as a function of the control signal derived from the exhaust gas sensor. This carburetor component is continually displaced, either toward a richer or leaner mixture condition, thus in effect integrating the signal from the exhaust gas sensor which ultimately regulates the air/fuel ratio. Operation of the control circuit is modified as a function of the engine speed and the engine temperature.