Abstract: A control circuit for delivering control signals to interrupt admission of the fuel-air mixture in the low speed and idle circuit of the carburetor of an internal combustion engine. The control circuit is operated according to the engine operating conditions. The control signal is delivered in response to comparison of a signal whose level is representative of the positive or negative variations in the duration of an engine cycle with a substantially periodic signal to generate a pulse shaped signal. The width of the pulses increases when the vehicle is accelerating and decreases when the vehicle is decelerating.