RE: Jett 50 problem
agree with Rich.........with a 10x6 you should be hitting somewhere around 16-16,500 easily.
i don't own a torque wrench and i like the idea of using one, but i never run engines lean so haven't had anything loosen up.....might even say my pattern of mechanical setup and checking is rather boring, but competition teaches you that. but like Rich said, if you have run lean and the holdown screws have loosened enough to allow the sleeve to rotate, then that will make a sudden change like you just experienced.
here is a picture of where i have my needle mounted. 6 flights so far and haven't touched a thing, but the 50 is showing signs of more power, not less. i'm still on the original plug too, and that includes 40 minutes of breakin.
these engines are the smoothest and most consistent engines i've run yet.