Hi Guys

I have a problem in my datto it smokes a bit in higher rpm and smells fuel and also engine idle speed vary depend on the engine temp and also sometimes when i engage clutch it increase rpm(but not always), my mechanic said the Idle Air Mixture screw doesn't funtion so he can't tune the engine he was trying his best but could not sort out the issue.

what would you guys think ?
what cause this to happen ?
i am going to try it on next Saturday again so need your guys help

thanks
Regards
sumith