RE: Seagull Decathlon engine
That is a great plane. I flew mine with an os .61 2 stroke. I liked it but it needed more so i went for the saito .84 four stroke. Works great. Flying with a 14*6 prop. A little fast on landing with that but i am going to try it with a 13/8 three blade this weekend. There is lots of information on that plane here.