RE: YS110 fz-s idle issues
Sounds more like a problem with the servo than it does the engine. Are you sure the servo isn't binding or something? Or maybe the throttle barrel is not moving freely so that it's taking a long time for it to move after you move the throttle stick back to idle.
You need to be able to see the throat of the carb and see if, after you bring the stick back to the idle position, the carb barrel is rotating to the closed position immediately, or if there's a lag. If there's a lag, you'll have to find out why. If there is no lag, but the engine is continuing to run too fast even after the throttle closes, then I'd suggest you have a serious air leak somewhere that's letting the engine suck air past the barrel. Find out which it is and maybe one of us can help you figure it out.
David