First, when you get the bike started, and after you can close the choke(enrichment lever up) and keep it idling, slowly turn the big-headed screw in until you have a little bit higher idle speed than you want, but not much higher. Just enough to be very stable and a very little bit above normal idle speed.
Let the bike warm up for a couple minutes.
Then turn the little air-bleed screw slowly out, and see if the idle speed increases. If it does, play around with it until you achieve the fastest idle speed you can get by turning that screw.
If turning out doesn't do anything, then try slowly turning it in, and see if you can get the idle speed highest by doing that.
The goal is to turn that screw, either in or out, whichever way works, to get the highest idle speed that you can find with that screw.
Don't turn it any more than one turn in either direction. If you can't get the highest idle speed within one turn in or one turn out, then report that to us here.
Once you find the place where the idle air-bleed screw gives the fastest idle, then leave that screw right where it is.
If that was successful, you now have a warmed-up bike that has a fast idle.
You may now lower the idle speed by turning the big-headed screw out slowly, until you get a decent idle speed, not too slow, and very stable.
Once that is done the bike should run good, and not stall at a stop-light.
If it doesn't work out good, then we'll need to look deeper.
Just see if that does the trick for you, and tell us if it does.