Known rotary-type carburetors have a fuel-and-air mixing passage orientated through a body for flowing a controlled ratio and volume of a fuel-and-air mixture to a combustion engine. This control is generally provided by a throttle valve rotatably and axially movable in a cylindrical cavity transverse to the mixing passage. A cylindrical portion of the throttle valve located in the cavity carries a through-bore that when rotated generally aligns adjustably to the mixing passage generally controlling the mixture flow rate. The cylindrical portion also supports a needle orientated concentrically to a rotary axis of the throttle valve and projecting into the through-bore for receipt into an open end of an axially confronting fuel feed tube supported by the carburetor body. A cylindrical wall of the feed tube carries an orifice opening into the through-bore for the flow of liquid fuel into the mixing passage and from a fuel metering chamber communicating with the feed tube. Axial movement of the rotary throttle valve shifts the needle axially with respect to the feed tube thus adjustably obstructing the orifice thereby controlling fuel flow into the through-bore and mixing passage.
Generally, a cammed interface between the cylindrical portion of the throttle valve and the carburetor body acts to move the throttle valve axially in response to rotational movement of the same. Rotational movement is achieved through operator intervention generally placed upon a throttle lever disposed outside of the carburetor body and typically engaged to the cylindrical portion via a rotatable valve shaft.
Such rotary-type carburetors are known to have engine start devices that act to supply an enriched fuel-and-air mixture to a cold engine for starting. These start devices typically carry cam surfaces required to cause axial movement of the throttle valve. Unfortunately, known start devices have numerous parts and the known cam surfaces require structure that projects further outward from the carburetor body than does the throttle lever at its furthest axial withdrawn (wide open) state thus considerably enlarging the carburetor size. Moreover, known start levers having a handle or knob at a distal end for leverage that must also project a considerable distance from the carburetor body hindering a desirable compact carburetor design.