Abstract: A rotary valve system mounted to an internal combustion engines and method of operating the system primarily comprises a rotary valve mounted within a valve sleeve, which is in turn mounted within a longitudinal bore extending through an intake and exhaust manifold. Controllers vary the rotational and axial position of the valve sleeve, which provides the capability of adjusting the amount of fuel mixture entering the combustion chambers of the engine and the timing of the intake of such mixture. The method of operation includes in taking fuel mixture into, and evacuating exhaust gas from, an internal combustion engine, wherein fuel mixture flows into the manifold, is directed across the valve sleeve, through the rotary valve, across the sleeve, and into a combustion chamber. After combustion of the fuel mixture, the exhaust gases are directed from the combustion chamber through the sleeve, through the rotary valve and into an exhaust chamber.