Having the same issue, BUT on my first run I did not have this issue, bike ran pretty well, now runs, cuts out, the vent is in the open position of course, any way to clean the cap so it flows better, but also did it with cap off, so maybe cap is ok? Fuel line leaks a bit from petcock to carb, so maybe vacuum is sucking the line closed? It always starts back up, but only runs about 30 seconds now. Thoughts? 78 Express. For what it is, this bike rides nice, I love my QT-50, but this rides better, but I think Yamaha owned the noped market, love the kick start and shaft drive.