I notice airtime mentioned synthetic fuel, that's not a bad way to go. I have tried it, not the green though and it is a much cleaner fuel. The bulk of the snot is the Castor oil. My number one brand fuel has always been Power Master 15/18. The 18% oil is fine but being a blended fuel there is still a lot of nasty snot blowing out. When I could no longer get Power Master I went with Wild Cat 15/16, much cleaner but 16% oil gave me pause so I added in two ounces of Klotz oil, that brought back the snot factor though. I'm now able to get the Power Master 15/18 again so I will be leaving my Klotz for my gas engines. If it's just the clean up that's the problem then buy a jug of full synthetic and give that a try. By placing my engines on there side or inverted I'm able to deflect the snot away and have very little clean up. I have one plane with an upright engine and it's a total mess after one flight, even with the deflector. There is just no good place to deflect the exhaust.