Ok. I ran it with the plane up side down. Guess what, runs just as good as it did on the bench. This is very frustrating. So much for my installation being wrong. Why are these engines so difficult to use? I've had 3 YS engines and they have all been a pain. They are great when they run right. Tons of power. But, at least for me, they are very difficult to tune. Especially when they are inverted. I am going to try a glow driver next.