I have two identical 1990 bayou 220's. One is driving me nuts. The compression is at 175. the valve clearance is in spec. I put a rebuild kit in the carb, new rubber on both sides of the carb. It starts very good runs smooth and quiet, no smoke. but once its hot and you come to a stop the idle is racing. I can turn out the idle stop screw and it drops down, but next stop it will be racing again. Pulled the spark plug and its covered in carbon soot. Any suggestions?