Running out of gas w/ 1/4 tank

[icabodcam]

I'm embarrased, and angry, and confused all at the same time.  Got my bike running very well after all these years (thanks Buddha and all for the advice for the carbs, was a cloged pilot), and spent yesterday putting on lots of miles.  Even took my wife out for a ride or two.  This morning I grabbed the bike to ride out with the wife to get some biscuits, and the thing started stuttering at speed, then ended up stalling.  I was thinking major problems, but hit the starter, and got nothing.  I tapped the bowl on the left side, and got a hollow plink, seemingly empty.  "Out of gas", I thought, "how, I just filled up?"  I primed, then shifted the petcock to on, and got started.  Half a mile down the road, did it again. 

This time I checked the tank.  There seems to be quite a bit of fuel in the tank, so I primed again, and this time shifted to reserve.  This time it lit right up, and rode like a charm all the way home.

What am I missing?  I don't remember this think running out of gas with fuel in the tank, is this bad memory?  I was thinking perhaps that the on setting is vacume driven, maybe I've a vacume problem.  Maybe a pinched line, though visual inspection dosen't support that, nor the miles I put on yesteraday.  To complicate this thought, I was warming up with the bike on the side stand, and got a fuel overflow, but when holding the bike up, no problem. This may be two seperate problems, I don't know, somebobdy help. 

[bikejunkie223]

You are running out of fuel in your main tank and have to put it on the reserve. The main tank holds roughly 4 gallons and is good for about 225 miles or so if you ride reasonably, then you need to put it to reserve to access your additional 1.3 gallons

[theGrinch]

+1

Reserve is vacuum operated as well.