Abstract: A system for simultaneously injecting propane and gasoline into an internal combustion engine. A propane supply reservoir is connected to the engine carburetor by a first line. A metering valve is positioned in the first line and has a vacuum responsive valve actuator associated therewith. The vacuum responsive actuator is connected by a second line to the EGR valve which creates a stronger vacuum with increasing engine speed. As the vacuum strength increases, the valve actuator opens the valve further allowing more propane to flow into the carburetor which is also drawing vaporized gasoline through conventional means. Preferably, an air aspirating device is positioned in the first line between the valve and carburetor for mixing air with the propane.