Maybe I wasn't clear in what I asked you. When you run that engine with a prop on it as it appears in your video, there would be a lot of air flowing across it to cool it. If you ran it WITHOUT the prop on it, I am assuming it would overheat very fast. Have you ran it for any periods of time without the prop. I am going to assume that it is like the Nemett Lynx and Bobcat---Great as an air cooled engine when ran with a prop, but if ran without a prop would probably need to either have the cylinder water cooled or have an auxiliary fan mounted blowing over the fins as I did on my recent build.