I have a BME 44 and was getting tired of the mess it was leaving on plane. I called Keith at BME and he said as long as I had two gallons of 40 to 1 mix with regular petroleum based oil I could then switch to synthetic mix at 50 to 1. He also mentioned that he had been meaning to change the number of gallons of breakin in the manual. I switched to synthetic after two gallons and have had no problems at all. I get 7600 rpm with a Menzs 20x8 prop and have a great low idle on the motor. I have 8 gallons through it and it is still getting stronger. If you don't believe me just call Keith, He has great customer service.