ive just bought a 140cc pitbike from classifieds, it has only been ridden 4-6 times and wear on the bike proves it as theres not a scratch, but ive just done my mixture screw, but now my idle screw has no effect, can u help?

 

Late to the party maybe but go to the Carb tuning sticky in this forum and start from scratch?
If your mixture is way off, the idle screw wont do bugger all.
Best I can suggest is start from the start. get it running and go from there.
Had a 49cc 2stroke here other day needed same treatment. Make it run, then run right.