Abstract: A molecular diffuser assembly is adapted to replace the carburetor of an internal combustion engine and is provided with a venturi-type passageway in communication with the internal combustion engine for drawing an airstream therethrough. A thermistor-type heater/evaporator assembly operates at a selected temperature to evaporate all the volatile constituents of the liquid fuel introduced thereto and provides a substantially complete vapor fuel for delivery to the venturi for diffusion with the airstream passing therethrough. A regulator assembly controls the amount of vapor fuel discharged into the venturi in response to parametric information delivered thereto, such information indicative of the mass flow rate of the airstream flowing through the venturi. The vaporized fuel in the venturi throat represents the fuel molecules at an optimal degree of separation so as to optimally react with the oxydizing airstream.