Abstract: A self-regulating, fast-response fuel vaporizer is disclosed which is cape of promoting increased efficiency of combustion of the fuel supplied to a spark ignition engine throughout the entire working range of the engine. The vaporizer comprises an inlet conduit through which fuel-air mixture is admissible to the engine, the mixture being directly heated within the conduit by an exhaust conduit which intersects with the inlet conduit. Use is made in the design of the respective heat transfer surfaces, of an inherent effect that flow pulsations have upon heat transference between a gas flowing in a tube and the walls of that tube, to provide a selected inverse relationship between heat transfer coefficient and engine speed whereby automatic regulation may be achieved of the heat supplied to the fuel-air mixture for all engine speeds.