For Sale an almost new O.S. 81FS-a Ringed 4-Stroke Engine w/Muffler. About 1/2 a gallon of fuel through this excellent engine. I had it in a .46 U-Can-Do and it hauls it like a rag doll. With an APC 12.25-3.75 you can hover all day long and then shoot out like a lunar rocket. I fully guarantee this engine, if you are not satisfied send it back within seven (7) days and I will fully refund your money. Thank you for looking. I will post actual photos as soon as possible.