Staged carburetor

Claim 1

A carburetor for an internal combustion engine comprising: A. a body structure having at least one air/fuel mixture conduit therethrough, B. a throttle valve mounted across said conduit for movement from an open position to a position closing said conduit, C. means for operating said throttle valve, D. means for supplying fuel to said mixture conduit, E. a boost venturi having an air passage therethrough and centrally located in said mixture conduit above said throttle valve and having a main nozzle therein in communication with said means for supplying fuel, F. an unbalanced venturi valve means mounted in said mixture conduit for obstructing the flow of air around said boost venturi when said venturi valve means is in a closed position, G. means for biasing said venturi valve means toward a closed position whereby said venturi valve means is closed at least during a portion of the part throttle range of operation of said carburetor, H. an idle fuel system in communication with said means for supplying fuel and having a discharge port adjacent an edge of said throttle valve for supplying fuel during idle and low part throttle operation of said carburetor, I. restricting orifice means including an adjustable metering element in the said means for supplying fuel to said main nozzle, and J. positive opening control means for said venturi valve means comprising linkage means including lost-motion connecting means connecting said venturi valve means to said throttle valve operating means for controlling the opening thereof to thereby maintain high air velocity in said boost venturi throughout the part throttle operation of said carburetor.