You are using a fuel containing 15% of oil, according to me 15% is low it would be better to raise the amount of shell to 13%, the loss of power is negligible but your engine will last much more.Last summer I experimented 15%of molysint in a S.T.G90 the engine run perfectly,the model was very clean........ after about 5 liters of these fuel the big end of the conrod was gone.