Abstract: The present invention provides a diaphragm carburetor wherein heat transferred from the engine to the carburetor through the insulator is reduced to lower the temperature of the carburetor unit and reduce the occurrence of bubbles in the fuel. The carburetor of the present invention is a diaphragm carburetor in which a fuel channel that extends from a pump chamber of the carburetor to a constant-pressure fuel chamber is divided into two branches to form one branch as a main fuel channel connected to the constant-pressure fuel chamber, and the other branch as a fuel circulation channel for passing the fuel through the body side surface of the carburetor on the insulator side, or the body side surface of the insulator on the carburetor side, causing the fuel to make a circuit around the carburetor, and returning the fuel to the fuel tank.

Abstract: A carburetor start pump circuit, for starting an engine has an auxiliary fuel pump mounted on a relatively standard carburetor body, a start pulse passage extending through the carburetor body to the auxiliary fuel pump, and a fuel circuit having an intake side which extends from a metering chamber of the carburetor body to the auxiliary fuel pump and a discharge side which is interconnected to the intake side and extends from the auxiliary fuel pump to a throttle bore in the air intake of the carburetor body. To prevent the engine from stalling, a restriction jet is placed within the start pulse passage to prevent the auxiliary fuel pump from discharging fuel into the throttling bore when the engine transmits pulses at high frequencies.

Abstract: Methods of operating a diaphragm type carburetor to facilitate the atomization of fuel in the diaphragm-type carburetor are disclosed. Particularly, methods of operating a diaphragm-type carburetor having a check valve installed in a fuel passage leading from a constant-fuel chamber to a main nozzle, and an air bleed passage connected at a position on the downstream side of the check valve are disclosed. Moreover, techniques for operating a diaphragm-type carburetor having a main nozzle including nozzle openings facing downstream with respect to the engine intake air flow are also disclosed, wherein the nozzle openings are located in a tubular member cutting across a central axial line of the venturi so that the tubular member bridges the neck of the venturi.

Abstract: A valve opening mechanism for a rotary throttle valve type carburetor having a lever which transmits the accelerator operation to the throttle valve. The lever and throttle valve are turned while the throttle valve is simultaneously caused to move in the central axial direction from the idle position by a cam part. This movement slightly increases the degree of overlap between a throttle orifice in the throttle valve and an air intake passage in the carburetor body, and slightly reduces the depth of insertion of a metering needle into the fuel nozzle. As a result, the amount of air and fuel is increased to an amount necessary for low-temperature starting. In operation, the cam part engages with the lever and is fixed in the operative position. Then, the lever is released by the normal operation of the accelerator, and is returned to the inoperative position by a return spring.

Abstract: A valve opening mechanism for a rotary throttle valve type carburetor having a lever which transmits the accelerator operation to the throttle valve. The lever and throttle valve are turned while the throttle valve is simultaneously caused to move in the central axial direction from the idle position by a cam part. This movement slightly increases the degree of overlap between a throttle orifice in the throttle valve and an air intake passage in the carburetor body, and slightly reduces the depth of insertion of a metering needle into the fuel nozzle. As a result, the amount of air and fuel is increased to an amount necessary for low-temperature starting. In operation, the cam part engages with the lever and is fixed in the operative position. Then, the lever is released by the normal operation of the accelerator, and is returned to the inoperative position by a return spring.

Abstract: The present invention serves to facilitate atomization of fuel in a diaphragm type carburetor for all-purpose two-cycle engines. A check valve used to prevent back flow is installed in the fuel passage leading from a constant-fuel chamber to a main nozzle, and an air bleed passage is connected at a position on the downstream side of the check valve. The main nozzle is constructed by forming nozzle openings which face downstream with respect to the engine intake air flow. The nozzle openings are located in a tubular member which cuts across a central axial line of the venturi so that the tubular member bridges the neck of the venturi.

Abstract: A diaphragm type carburetor is disclosed wherein a cantilever portion is used to augment the resilience of a first diaphragm and return it to an undeformed position during the neutral signal produced by a 4-cycle engine. The cantilever portion cooperates with the intermittent vacuum signal from the crankcase piped to one side of the first diaphragm so as to oscillate the diaphragm and draw fuel from the fuel tank of the engine into the carburetor. The device is also suited for use with 2-cycle engines which produce both vacuum and pressure pulses wherein the cantilever portion is used to augment either pulse to improve the performance of the fuel diaphragm.

Abstract: The object of the present invention is to easily provide an appropriate amount of starting fuel for all-purpose engines, without requiring any special skill. The upstream side and downstream side of a throttle valve in an air intake passage are connected by a bypass. This bypass and a constant-fuel chamber are connected by an increased-fuel passage which is equipped with a check valve. The system is arranged so that the bypass and increased-fuel passage are opened and closed more or less simultaneously by an opening-and-closing valve. The necessary amount of starting fuel can be supplied to the engine in a short time by means of the increased-fuel passage, so that starting can be accomplished by cranking the engine a few times. The flow of air into the constant-fuel chamber from the bypass is prevented by the check valve so that rough idling and the need to expel inflowing air are eliminated; and starting operations may be performed in any desired order.

Abstract: In a first aspect, a carburetor fuel adjusting device that facilitates control of the quantity of fuel that flows from the fuel chamber to an air intake port of a carburetor by making it possible for the user to adjust an adjustment valve within the limits defined by emission control regulations. The carburetor fuel adjusting device has a cap having two appendages, and an engagement area to engage a valve extension of the fuel adjustment valves of a carburetor. The cap is retained by the retainer in either a disengaged position, or an engaged position wherein the engagement area of the cap becomes attached to the valve extensions. In the engaged position, the adjustment valves can be turned in unison with the cap within a range formed by the angle between the appendages which, when rotated, abut against stoppers.

Abstract: In a first aspect, a carburetor fuel adjusting device that facilitates control of the quantity of fuel that flows from the fuel chamber to an air intake port of a carburetor by making it possible for the user to adjust an adjustment valve within the limits defined by emission control regulations. The carburetor fuel adjusting device has a cap having two appendages, and an engagement area to engage a valve extension of the fuel adjustment valves of a carburetor. The cap is retained by the retainer in either a disengaged position, or an engaged position wherein the engagement area of the cap becomes attached to the valve extensions. In the engaged position, the adjustment valves can be turned in unison with the cap within a range formed by the angle between the appendages which, when rotated, abut against stoppers.

Abstract: A fastening member made of an elastic material is press-fitted in a gapless manner in an insertion hole that divides screw holes in a carburetor body into forward and rearward sections. Screw rods of adjustment valves are screwed into the screw holes and through screw through-holes formed in the fastening member. The screw through-holes have female screw-threads formed by thread rolling. The female screw-threads maintain pressing contact with the surfaces of male screw-threads on the screw rods as a result of the elastic recovery force of the female screw-threads, so that rattling and fuel leakage tend to be prevented.

Abstract: A valve opening mechanism for a rotary throttle valve type carburetor having a lever which transmits the accelerator operation to the throttle valve. The lever and throttle valve are turned while the throttle valve is simultaneously caused to move in the central axial direction from the idle position by a cam part. This movement slightly increases the degree of overlap between a throttle orifice in the throttle valve and an air intake passage in the carburetor body, and slightly reduces the depth of insertion of a metering needle into the fuel nozzle. As a result, the amount of air and fuel is increased to an amount necessary for low-temperature starting. In operation, the cam part engages with the lever and is fixed in the operative position. Then, the lever is released by the normal operation of the accelerator, and is returned to the inoperative position by a return spring.

Abstract: In a first aspect, a carburetor fuel adjusting device that facilitates control of the quantity of fuel that flows from the fuel chamber to an air intake port of a carburetor by making it possible for the user to adjust an adjustment valve within the limits defined by emission control regulations. The carburetor fuel adjusting device has a cap having two appendages, and an engagement area to engage a valve extension of the fuel adjustment valves of a carburetor. The cap is retained by the retainer in either a disengaged position, or an engaged position wherein the engagement area of the cap becomes attached to the valve extensions. In the engaged position, the adjustment valves can be turned in unison with the cap within a range formed by the angle between the appendages which, when rotated, abut against stoppers.

Abstract: A carburetor start pump circuit, for starting an engine, has an auxiliary fuel pump mounted on a relatively standard carburetor body, a pulse passageway extending through the carburetor body to the auxiliary fuel pump, and a fuel circuit having an intake side extending from a metering chamber in the carburetor body to the auxiliary pump where it is interconnected to a discharge side extending from the auxiliary pump to a throttle bore in the air intake of the carburetor body. To facilitate control of fuel flow, the fuel circuit includes inlet and discharge check valves and a metering jet.

Abstract: A carburetor fuel adjusting device that facilitates control of the quantity of fuel that flows from the fuel chamber to an air intake port of a carburetor by making it possible for the user to adjust an adjustment valve within the limits defined by emission control regulations. The carburetor fuel adjusting device has a cap having two appendages to limit its turning in the lean mixture direction and in the rich mixture direction, and an engagement area to engage a valve extension of the fuel adjustment valves of a carburetor. The valve extensions are inserted through insertion holes of a retainer attached to the carburetor body. When the cap is retained by the retainer in a disengaged position, wherein the engagement area is not attached to the valve extensions of the fuel adjustment valves, the adjustment valves can be adjusted separately from the cap. The cap, however, can be moved forward to an engaged position wherein the engagement area of the cap becomes attached to the valve extensions.

Abstract: A carburetor fuel adjusting limit device that facilitates control of the quantity of fuel that flows from the fuel chamber to an air intake port of a carburetor by making it possible for the user to adjust a fuel adjustment valve within the limits defined by emission control regulations. The limit device has a cap that comprises an engagement area to engage a valve extension of the fuel adjustment valve and radially extending appendages to limit rotation. The construction of the engagement area, which includes axial and radial locks, enables the cap to be pressed onto the valve extension with a relatively low amount of force. The fuel adjustment valve includes a screw head attached to the valve extension and constructed to break away from the valve extension at a torque that exceeds about 8 kg-cm. A retainer is utilized to retain the cap in a disengaged position adjacent the valve extensions. Once the cap is pressed onto the valve extension the cap and the fuel adjustment valve rotate as a unit.

Abstract: A tamper resistant limit cap for a carburetor having manual adjust valves that are able to adjust the effective area of the main fuel passage and the slow speed fuel passage. The cap covers tightly on the head part of the main fuel adjust valve and includes a flange attached to the outside of the cap that abuts a stop upon rotation of the cap, a guide flange attached to the outside of the cap to locate, upon installation, the final position of the cap, and two projections on the inside of cap to prevent removal of the cap from valve head part or independent rotation of the cap and head part relative to each other.