M6 x1.0 is the most common size screw on these (think of the clutch cover screws)
id take one of those off and compare sizes, believe the carb idle screw is an M5x(0.8?), try and see if the magneto cover screw and see if it will work in it.
keep in mind the idle screw has a taper (for adjusting the idle up or down) so your gonna have to make that yourself.
id just buy a new carb, for 8$ your gonna spend that one 2 screws +shipping (or at least close to it) + the hassle of finding the right one, trial and error, etc.