Fuel regulating mechanism and method for a rotary throttle valve type carburetor

A method of regulating fuel feed from a carburetor to an associated engine in which the carburetor has a rotary throttle valve with a throttle hole disposed in an air intake passage of the carburetor body, and wherein the quantity of air flow in the air intake passage is controlled by at least rotational movement of the throttle valve to thereby vary the opening area of the throttle hole exposed to the carburetor intake passage for controlling air flow therethrough, the throttle valve being cylindrical and rotatable about an axis transverse to the axes of the throttle hole and carburetor air intake passage, the throttle valve also being axially movable along its rotational axis during such rotational movement and a quantity of fuel is released from a fuel jet port of a fuel supply pipe secured to the carburetor body as controlled by the relative position to such jet port of a fuel regulating needle attached to the throttle valve for axial movement therewith, 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 an idle speed fuel quantity has been set prior to fitment of said closing member, the carburetor further having a bypass air passage for variably communicating the throttle hole of the throttle valve at an upstream portion thereof with an air source comprising ambient atmosphere or the intake air for the carburetor and in bypass relation to the opening area of the throttle hole exposed to a bypass air passage outlet at engine idle setting of the throttle valve, and wherein said bypass air passage outlet is 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, said method comprising the steps of:

• (a) at initial carburetor-to-engine set-up and calibration maintaining the bypass air passage open while the engine is running at idle speed, (b) during the conditions of step (a) adjusting the fuel-regulating needle to provide the maximum fuel to air (F/A) mixture ratio permitted by applicable engine exhaust air quality regulations,
• (c) then permanently setting said fuel needle adjustment by non-removably fitting the closing member to prevent exterior access to an adjustment portion of the fuel needle,
• (d) then thereafter during subsequent end user operation of the engine closing the bypass air passage only when preparing to crank the engine for starting to thereby provide an enriched fuel-to-air mixture for starting of the engine, and
• (e) thereafter, upon engine starting and running under its own power, reopening the bypass air passage.

A method of regulating fuel feed from a carburetor to an associated engine in which the carburetor has a rotary throttle valve with a throttle hole disposed in an air intake passage of the carburetor body, and wherein the quantity of air flow in the air intake passage is controlled by at least rotational movement of the throttle valve to thereby vary the opening area of the throttle hole exposed to the carburetor intake passage for controlling air flow therethrough, the throttle valve being cylindrical and rotatable about an axis transverse to the axes of the throttle hole and carburetor air intake passage, the throttle valve also being axially movable along its rotational axis during such rotational movement and a quantity of fuel is released form a fuel jet port of a fuel supply pipe secured to the carburetor body as controlled by the relative position to such jet port of a fuel regulating needle attached to the throttle valve for axial movement therewith, 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 an idle speed fuel quantity has been set prior to fitment of said closing member, the body of the carburetor further having a bypass air passage for variably communicating the throttle hole of the throttle valve at an upstream portion thereof with an air source comprising ambient atmosphere or the intake air for the carburetor and in bypass relation to the opening area of the throttle hole exposed to a bypass air passage outlet at engine idle setting of the throttle valve, and wherein said bypass air passage outlet is constructed and arranged in the carburetor body 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, said method comprising the steps of:

• (a) at initial carburetor-to-engine set-up and calibration maintaining the bypass air passage open while the engine is running at idle speed,
• (b) during the conditions of step (a) adjusting the fuel-regulating needle to provide the maximum fuel to air (F/A) mixture ratio permitted by applicable engine exhaust air quality regulations, and
• (c) then permanently setting said fuel needle adjustment by non-removably fitting the closing member to prevent exterior access to an adjustment portion of the fuel needle.

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 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 and wherein the throttle valve is movable along the 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 a bypass air passage is provided in the carburetor body variably communicating the throttle hole of the throttle valve at an upstream portion thereof with the 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, 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 an idle 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 to thereby de-register the throttle hole with said bypass air passage outlet, the improvement in combination therewith wherein said bypass air passage is constructed and arranged so as to be maintained open when said adjustment of needle regulation is being set and also during engine running at idle speed.