Abstract: A resiliently deformable link is interposed between the throttle linkage and the throttle lever of a carburetor normally associated with a conventional internal combustion engine. The resiliently deformable member receives and stores energy during acceleration movements of the linkage and transmits the energy to the throttle lever for opening the throttle valve. A pneumatic restrictor such as a dashpot or bellows opposes the opening of the throttle valve in response to the resiliently deformable member. The rate of discharge of air into or from a chamber within the pneumatic restrictor modulates the rate of opening the throttle valve. Air flow is regulated by air bleed means which may be an adjustable atmospheric vented valve or other means responsive to engine manifold vacuum.Biasing means serve to urge the throttle lever toward a closed throttle position.