Abstract: A system for vaporizing fuel and mixing it in controlled proportions with liquid fuel as a feed to a carburetor in an internal combustion engine comprising a vapor generator for heating liquid fuel to vaporize it, a jacket around the generator filled with a liquid heating medium, a means for controlling the heating of the liquid heating medium by exchange with the exhaust of the engine, a first temperature sensing means to detect when the vaporized fuel in the vapor generator reaches a predetermined value and signaling a controlled means to admit vaporized fuel to the feed line to the carburetor and correspondingly to reduce liquid fuel being fed to the carburetor, a second temperature sensing means in said jacket for controlling the amount of heat absorbed by the liquid heating medium from the exhaust, a first pressure regulator means in the vapor outlet of the vapor generator to direct vaporized fuel to the feed of the carburetor upon reaching a predetermined pressure in the vapor generator, and a second pr