Yesterday afternoon I got on the bike to leave work.  It turned over 2 or 3 times before starting, usually starts right up.  Idled rough and when I put it in gear it started off and then stalled.  I monkeyed some with the choke and could start it but it wouldn't stay cranked when I tried to roll away in first.  It seemed to be flooding out.  While thinking about what to do, I opened the oil fill and put in about a half pint cause I knew I was that low.  Got my tools out of the box, and used the flat screwdriver to turn the idle air screw.  (Actually the stock screwdriver is too wide to fit in the hole, so I filed it down some on the concrete.)  Richened the mix by turning counterclockwise about 1 full turn, as it had been at 1 1/2.  Opened the gas cap just to be sure it was as full as I thought; and it was, because I had just filled up about 16 miles ago.  Put my tools back in place, started her up and everything was fine again, drove 25 miles home.

So which of these things fixed it?  (1) Opening the oil fill cap; (2) adjusting the air screw; (3) opening the gas cap.

Probably not #1.  On #2, I had been feeling some slight surging at mid RPMs, so richening the mix probably helped, and indeed there is less surging now.  On # 3, there might have been a vapor lock of some kind that was relieved when I opened the cap.

Let me hear from you, Brain Trust!

Not real cold.  Temp down a few degrees, in the 70s, but humidity has dropped noticeably.  I've thought about that being a contributing factor maybe.  You think I should check the carb vents, huh?

Could be stuck needle valve! I had similar episode before