I have a 1999 OX66 on a Skeeter 202C. Some times it will get up to 5700 rpm's and other times only 5200 rpm's. About 20 hours ago and changed/cleaned all the filters and had the injectors cleaned. Also cleaned the O2 sensor by soaking in Seafoam for 24 hours but it was still black. Have any idea what else it could be?