Abstract: A fluid continuously variable transmission system that includes a body forming a cylindrical chamber. A rotor with blades positioned in the chamber is connected to a power input shaft. The rotor is rotatably movable relative to the body, which in turn is connected to a power output shaft. A valve, preferably a rotary plug valve, is connected to the rim portion of the body. The valve is movable between fully open and fully closed positions, and a plurality of intermediate positions therebetween. The body forms a fluid circuit between a high pressure channel from the chamber to the valve and a low pressure channel from the valve to the chamber. The rotor pressurizes fluid in the fluid circuit against the valve in proportion to the degree of closing of the valve which action rotates the body in all valve positions except the fully closed position.