You can't buy the power jet screws. You have to get a really good fitting screw driver, give the screw a smack and it should undo with a bit of a crack.

I used to run mine with the biggest power jets I could get (think its #80 or is it #75 I can't remember).

To quote Fontyyy, run jets that could power a space shuttle.
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If I have to take the carbs off once more...