1.  back the screw all the way out. (dont lose the spring)
2.  Remove the screw
3.  Use a dremmel tool with the smallest circular cutting blade you can find.
4.  Cut a new slice in the top of screw and you'll be good to go. The only part of the screw that is functional is the tip (the part inside the carb) and the spring.

May the force be with you