Walbro Japan, Inc.

Shin-Ichi Ohgane

Teruhiko Tobinai

Tamio Aihara

A carburetor for a two stroke engine with an air passage and a separate fuel and air mixing passage in a carburetor body and the passages having an air valve and a throttle valve, respectively. A coupling connects a valve shaft of the air valve with a valve shaft of the throttle valve and has an area wherein the valves are rotatable relative to each other corresponding to a difference between an opening and closing angle of the air valve and an opening and closing angle of the throttle valve. Preferably, when the throttle valve is in an idle position, the air valve is closed and the throttle valve can be opened through at least some angle from its idle position before the air valve is moved from its closed position. Also, the air valve is preferably fully opened when the throttle valve is moved to its fully or wide open position. Thus, at idle operation of the engine, the air valve is closed to prevent a scavenging air supply from being provided to the engine to avoid an overly lean fuel and air mixture in the engine. When the engine is moved sufficiently off idle, the air valve is opened to supply the scavenging air supply to the engine which facilitates removal of exhaust gases and reduces the escape of a fresh fuel and air mixture through the engine exhaust ports.

Carburetor for two-stroke engine

A carburetor for providing a fuel and air mixture and a scavenging air supply to a two stroke internal combustion engine has a throttle valve received in a fuel and air mixing passage and connected to a throttle drive for controlling engine operation and an air valve received in an air passage and selectively operably connected to the throttle valve by a lost motion coupling. Preferably, the throttle valve and the air valve are barrel-type valves each comprising an opening formed through a shaft extending transversely through and rotatable within an associated bore of the carburetor body. The lost motion coupling may comprise a pair of selectively meshed gears consisting of a first partial gear connected to a shaft of the throttle valve for co-rotation with the throttle valve shaft, and a second partial gear connected to a shaft of the air valve for co-rotation with the air valve shaft and having a gap between two adjacent teeth so that the first partial gear does not mesh with the second partial gear until the throttle valve has rotated to a predetermined angle or position from an idle position. A gear ratio of the gear pair is set in such a manner that the throttle valve and the air valve are simultaneously operable at a fully opened position to permit substantially unrestricted fluid flow through their respective passages in the carburetor body.

Carburetor with air and throttle valve for two-cycle engine

A carburetor for a stratified type scavenging engine has a scavenging air supply passage with an air valve therein, a fuel and air mixture passage having a throttle valve therein, a diaphragm which defines a negative pressure chamber on one side and an atmospheric chamber on its other side, and a low pressure passage that communicates a venturi portion of the fuel and air mixing passage with the negative pressure chamber. The air valve is responsive to movement of the diaphragm caused by the pressure differential across it to move the air valve between open and closed positions and a spring yieldably biases the air valve towards its closed position. The air valve is not directly mechanically connected or linked to the throttle valve. Thus, when the throttle valve is rapidly opened during engine acceleration, the air valve is not immediately rapidly opened and is not significantly opened until a sufficient pressure differential exists across the diaphragm. Therefore, during initial rapid acceleration of the engine from idle, the air valve prevents a significant flow of scavenging air to the engine to ensure a sufficiently rich fuel and air mixture is supplied to the engine to support the rapid acceleration.

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Miyagi, Japan

Shin-Ichi Ohgane