I tried adjusting the screw but honestly I couldn't hear a difference in RPMs. So I went with the "adjust till it's fixed" method. I gunned the throttle and let it snap back. Where it was originally, the rpms dropped to where the bike almost stalled. I leaned out the mix until that went away. I kept turning clockwise until I got a backfire, then backed it up between those two points. After a 20 minute stop & go ride in 95-degree heat, no more stalling. I'll see how it goes on the commute tomorrow.

It was working fine for a few days, then the stalling came back. Generally it is after I am holding the throttle at constant speed for a while, then slow down eventually to a stop. I have already bumped up the idle speed with no effect. I replaced the vac line from petcock to carb and it seemed much better, even after a longer ride. Then today I was riding about 8 miles at a constant 40mph. When I went to slow down for a turn, the engine bogged way down, nearly to a stall, then a HUUUUUGE KAPOW backfire, then it stalled. This happens with the petcock on ON and on PRI. I went back and tried to readjust my idle speed and my idle mix, but I haven't gone riding again yet. Any other suggestions? I am supposed to be making a longish (60 mile highway speed) run tomorrow afternoon so it's getting to be crunch time.

BTW, it does seem to be much worse in hot weather. Last night after I replaced the vac line it was about 75 degrees... now it is around 95.

Do you mean the blow-by tube from the engine to the air box? There was nothing in there. Or, did you mean the capped drain tube under the air box? That is empty as well...

Looks like I found it... it was the petcock. I had the thing apart and the diaphram looked good - I gave a little suction on the vac port and didn't feel any leaks so I figured I was good. The fact that she was still stalling and bogging while on PRI also threw me. I took the petcock off again, did the mod to manual and it's nice and smooth now.