Abstract: A fuel system for an internal combustion engine includes a fuel processing unit having at least one foot-actuated, split butterfly valve for controlling induction airflow and a plurality of fuel injectors for spraying fuel into the induction airflow. The split butterfly valve in the fuel processing unit includes a pair of butterfly flaps which rotate in opposite directions in response to throttle movement to insure symmetry of induction airflow through the unit. The butterfly valve is connected to the throttle by a tangential linkage which gradually increases the rate of valve opening responsive to throttle movement to provide smooth response characteristics. The fuel is injected at a temperature and pressure drop selected to produce flash vaporization of the major portion of the fuel in order to promote complete combustion.