Vacuum response type carburetor

Abstract

A motorcycle vacuum response type carburetor comprises a carburetor body having an upper portion, a lower portion, a diaphragm device disposed at the upper portion and a floating member disposed at the lower portion. The diaphragm device has a diaphragm chamber and a diaphragm comprised of hydrogen impregnated nitrile butadiene rubber separating the diaphragm chamber into an upper section and a lower section. A venturi passage extends horizontally through the carburetor body and a guide passage extends through the venturi passage. The guide passage has an upper end portion in communication with the lower section of the diaphragm chamber. A piston valve is movably disposed in the guide passage and has a head portion fixed to a central portion of the diaphragm. A needle valve for adjusting a jetting amount of a fuel is mounted to a lower portion of the piston valve and extends into the float chamber. A first communication passage communicates the lower section of the diaphragm chamber to the atmosphere. A second communication passage extends through the piston valve for communicating the upper section of the diaphragm chamber to the venturi passage. The second communicating passage has an opening at a lower end thereof which opens from a lower end portion of the piston valve and is in close proximity to the needle valve.