where can i find a throttlestop screw for a PY80 dirtbike?

Answer 1

Always give year, make, engine size and model # when asking questions.
Does a py80 have a throttle stop screw? or do you want to restrict the engine?
If it's the latter -
-Remove the carb
-Remove the top (where the cable goes in)
-Remove the cable from the slide
-Insert the cable through a couple of nuts (use more for more restriction) and re-install the cable on the slide (don't forget the spring).
-The nuts will prevent the slide from going all the way up.
-To fine tune the restriction, use washers.

Answer 2

It is probably a standard metric size.
Just go to the hardware store and by 4 or 5 different sizes, one should fit depending on how go of an eye you have for estimation.