My GS had some serious running issues when driving, but was just fine parked (idling, revving, etc...) So I took apart the carburetors and cleaned them (one was clean and fine, the other had obvious corrosion and filth).  Now I put everything back together and it's having problems (Murphy's law).   

The first thing I noticed was that when it started with full choke, the rpm was only about 3,000 instead of 5-6,000 before.  It then became evident that maintaining idle was an issue (it would die without intermittent throttle).  Adding more idle speed screw made it die.  I've been playing with the idle mix screws, but there's no overt difference with any differing number of turns (well between 1 & 4 turns out). 

When I can get it to stay running (can't figure out what I do that makes it decide to run) I maintain rpm at 4,000, but after a while it gives a little stumble. So I give it a little more throttle to rest at 5,000 rpms.  Here's where it gets interesting...

After about 15 seconds of 5,000 rpm (with fixed throttle) the rpm will give a slight surge and then the engine will die.  After this it is difficult to start again.

Things I changed in the carb:

I found the #4 washer (one on each carb) that goes with the needle to be on the spring side of the E-clip, so I put it on the doughnut side (as per the pictures I've seen on gstwins)

The float height was below specifications on the right carburetor, so I bent the tang accordingly.

Anticipatory answer:

New gas comes out of the drain screw hole regardless of petcock position at any time I check it.

thanks for any help!

So my roommate thought percussive maintainence on the float bowl with the handle end of a phillips #2 would fix it...

Turns out he's right.

Someone make sense of that!

you float needle or slide was stuck. Same thing happened on mine, and I did the exact same thing with a screw driver and it fixed it.