Vacuum fuel valve (external, GX-moto). The valve opens the fuel supply to the carburetor only while the engine is running: vacuum in the intake tract moves the diaphragm, and when the engine stops the supply is shut off.
Replace it if gasoline leaks, if the engine stalls while riding or starts poorly because of a poor fuel supply — a torn diaphragm is often to blame. Before installing, check the hoses and the filter so as not to contaminate the new valve.
