I race this quad. I sees extremely demanding conditions, mostly dust, hard throttle and sustained rpms. The most recent sample is Silkolene Pro 4 SX in 15w50. It is a full ester oil, I was just curious how it would perform in this engine. The previous two samples are Schaeffer's Racing 5w50. I was very happy with the Schaeffer's, just curious about the Silkolene and needed to use it up, looks like it did very well. I took the sample on a cold engine, concerned about the fuel. I know this fuel injected engine has a very rich start and cold idle mode, I tried to avoid it by sampling cold, but it seems I may have a fuel problem.