please help my os r2102 won't drop down to idle quickly even when very rich (carb back at factory setings) the more you try to put a tune on it the worse it gets.things i've tryed sofare throttle closing properly,new plug,fresh fuel,rebuilt clutch,new engine bearings,new rod and checked for any visable leaks.don't want to run a new engine in incase some thing else is causing the problem.any help on how to find the fault.