Abstract: The invention is a rotary throttle valve carburetor that minimizes frictional drag on the airflow through the air intake passage. This is accomplished by providing bearing shafts at both ends of the rotary throttle valve body upon which are mounted ball bearings such that upon assembly of the rotary throttle valve body to the carburetor body housing, friction free rotation is established as the rotary throttle valve body is rotated by an accelerator cable from idle to full throttle position. The rotary valve carburetor also features a rotary throttle valve body assembly which by the use of end caps mounted to the rotary throttle valve body provides the ability to vary the venturi effect within the air intake passage by exchanging the rotary throttle valve body assembly and associated end caps with a different face angle so as to create a different venturi effect by the air passing through the air intake passage of the carburetor body housing.