stalls on any throttle with low tank.

[1N23456]

Having a new problem with my 08 - was cruising down the highway last week when the engine cut out on me.  Figuring it was just low, I switched to reserve, but the bike refused to run right.  I just spent all of today cleaning and rebuilding and synchronizing the carbs, which was a great learning experience, but it seems to have gotten me nowhere. 

Symptoms:
When cold or warm, it will only start with full choke
With full choke, it switches between running at 1500 or around 4000 RPM. 
With full choke, as soon as I touch the throttle it bogs down and dies
With choke off, it dies immediately, even when warm.

I added a gallon of gas to dilute the seafoam I had tried, and voila, after about a minute it picked right up and ran great.  But after I rode around for a while and burned up that gallon or so, it cut out again.

Thoughs?  My other idea had been a clogged line or something, but I blasted everything out with compressed air while it was apart today.  It also behaves the same with the petcock at on or reserve.

[Joolstacho]

I'd be looking at the fuel tap Vacuum system for a start. Try running it on prime and see if it still cuts out.