Perhaps back off the screw all the way out and see if you can get a replacement with a standard phillips head ( be careful, I believe there is a spring there when you back all the way out ).
First order of business for me was to buy a clone carb and rebuild kit, just to have it, its basically the heart of the bike.
I think you are going to get to a point where you strip or damage that screw and create a problem for yourself.
Get it out of there and get a regular screw in.
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