Arun
I have three Jen engines .37,.47,.57 I had problems running them on 10% nitro, as soon as I followed the Just Engines instructions and ran them on 5% nitro the problems vanished and they are now super engines (Jim had the same problem with his .57 last week and again 5% fixes the problem), it also cheaper
I agree with Gerard the Cougar is great with the .37 and is a superb plane.
Rod