Abstract: A water-augmented fuel and air supply system for an internal combustion engine which draws heated air into its intake manifold through two paths, one carrying the bulk of air, referred to as leaning air, drawn directly into the manifold, and the other providing a smaller stream of mixing air through a fuel and water vaporizer heated by engine exhaust. In the vaporizer, the heated mixing air flow acts upon a pool of liquid water and fuel to stimulate vaporization thereof. As engine temperature and engine exhaust temperature rise, the maximum vaporization stimulation effect of the impinging mixing air is no longer needed and is correspondingly reduced. The result is to permit cold starts and to provide a lean mixture of vaporous mixing air conducive to sustained economical engine operation, and increased power availability from the engine without incurring excessive rise in engine operating temperatures.