I have recently rebuilt an older Stihl ms201t and now I cannot slow the idle down! I have installed new piston rings and ported the muffler. The only re-conditioning I did to the carb was to replace the plastic metering diaphragm and on the other side, the rubber pump (diaphragm). It starts easily and cuts like a beast but I cannot adjust the idle down. The LA (idle adjustment) screw has been backed all the way out so it is not even touching the throttle stop. I have made minor and major adjustments to both hi and lo screws, starting at the owners manual suggested settings, but does not alter the idle rpms very much at all. I am not using a tach on it, just going by sound and how fast the chain is turning. At this point the idle appears to be nearly a third throttle, too fast to be safe with the chain turning so fast at rest. What have I done to this beast?! Also, the "hi" carb screw has a plastic limiter which gives me barley half a turn either direction. It is a stock, Stihl/ZAMA C1Q, S280 carburetor.