Abstract: Apparatus for limiting the speed of motor vehicles, especially small motorcycles, which have a carburetor provided with a fuel control element, wherein the fuel control element is responsive both to a signal generated by the driver and to an automatic control system which is responsive both to engine speed and vehicle speed. A displaceable stop member for limiting speed increasing displacement of the control element is driven by a servomotor controlled by a bridge switch circuit which is responsive to a comparison between control signals derived, respectively, from the position of the control element and the engine or vehicle speed. In the absence of a vehicle speed signal, an electronic switch automatically couples engine speed control signals to the bridge circuit.