I run my bushing rod ST90 at 16:1 oil using Redline. I also use the same fuel in my converted ST51 and Saito 91. No problems with any of them and the little 51 is turning just over 15,000 on the ground. By 16:1 I mean 8 oz of oil to a gallon of gas. I've run the two strokes at 22:1 which the four stroke tolerates just fine but the two strokes will eat the bushing if you get a real lean run. I just run the two stroke mix now in all of my conversions with bushings.