Mary Hinge
Forum Apprentice
Sorry if I didn't make it clear enough, with vacuum only reserve and prime have full flow and on has a trickle, without vacuum only prime has flow. I'm puzzled as to why ON doesn't work, I took the petcock apart and the diaphragm looks fine and the filter screen on the pickup tube looks fine, took it for a ride today and seemed to work on reserve but was getting some hiccups at cruising speed so I switched it to prime and seemed to smooth out. I tried to put my old petcock back in the but the seal around the switch is leaking and I don't have a replacement for it so I guess for now I'll just run this one on Prime and shut it off when I get done.
If the fuel level was low then that's exactly what you'd expect the fuel tap to do when the bikes running. If the tank isn't low then everything points to either the diaphragm being Donald or the fuel tap (On" tube/passage being blocked.