Fuel regulating mechanism for a rotary throttle valve type carburetor

In a fuel regulating mechanism for a carburetor in which a throttle valve having a throttle hole is disposed in an air intake passage of a carburetor body, and wherein the quantity of air flow in the air intake passage is controlled by movement of the throttle valve to thereby vary the opening area of the throttle hole exposed to the intake passage upstream of the throttle valve, and a quantity of fuel is controlled by a relative position of a fuel regulating needle attached to the throttle valve to a fuel jet port of a fuel supply pipe secured to the carburetor body due to movement of the throttle valve, and wherein the throttle valve is cylindrical and rotatable about an axis transverse to the axes of the throttle hole and carburetor air intake passage for controlling air flow through the carburetor air intake passage and wherein the throttle valve is movable along an axis transverse to the axes of the throttle hole and carburetor air intake passage for controlling air flow through the carburetor air intake passage, the improvement in combination therewith of a bypass air passage for variably communicating the throttle hole of the throttle valve at an upstream portion thereof with the air intake passage of the carburetor body in bypass relation to the opening area of the throttle hole exposed to the air intake passage at engine idle setting of the throttle valve, wherein an air quantity regulating needle valve is provided in said bypass air passage to variably adjust the quantity of air flowing in the bypass air passage to the throttle hole, wherein a closing member is non-removably fitted in said carburetor to permanently prevent exterior access to an adjustment portion of the fuel regulating needle located at one end thereof, and the end of the needle opposite said one end is inserted into said fuel supply pipe so that the adjustment of needle regulation of said fuel jet port cannot be made from outside of said carburetor after a low speed fuel quantity has been set prior to fitment of said closing member and wherein said bypass air passage has an outlet constructed and arranged relative to said throttle valve so as to be closed by movement of said throttle valve out of idle setting toward high speed and/or maximum power setting and thereby de-register the throttle hole with said bypass air passage outlet.