Abstract: An automatic cold start and warmup system for an internal combustion engine carburetor comprises a coiled bimetallic spring element actuating a choke valve mounted across the induction passage of the carburetor to control air flow therethrough. Two PTC heating resistors are located in heat-transfer relation with the bimetallic element, have different switching temperatures and are connected in series with a source. A switch closes above a predetermined temperature level of the engine and short-circuits the resistor having the lower switching temperature.