A piece of crud in the float valve, stuck maybe,
Rap on the carb with a screwdriver handle.

Drain the bowl into  clear container, see if its got crud..


How old is it?
And this is no big deal. Youll be fine.

Update: drained the bowl like you said, some white gunky stuff that kinda looked like mucus was in there. Unfortunately, the screw won't tighten back into it, so there's another problem.

If you pulled the screw out, put itup to a light, make sure you havent messed upthe threads, the very first one is critical. repair with small triangle file if necessary.
hold it up in place , turn backwards, till you feel a click.Thats when the threads line up.

Fingertips, small screwdriver.
Maybe clear threads, shoot Berymans up in those threads.
If it's not wanting to play fair, you may have messed it up.
You should probably pull the carb, get the JIS tools, pull the bowl, maybe chase the threads. I dunno if they go through. If so, from inside the bowl, run a good screw down, reshaping the threads. If not, a tap, BUT, be careful to Not cut new threads, its really important to just recreate the original threads.

The reverse rotation,click, serious help.
I. Use that with plastic all the time.

If they have been in, never removed, you'll play the dickens getting them.
Start by dosing them with the 50/50 acetone and transmission fluid penetrating oil for a coupla days, get JIS tips , antisieze , and, best to go back with SS Allen heads.Try , but don't be surprised if you need to pull the carb.