I've learned the trick with evolution is to get rid of the needle adjustment limiter, the limiters are there to prevent less experienced pilots from messing up the needle adjustments, at the same time it limits those of us with the experience needed to fine tune a engine to run perfectly, once you get rid of those limiters these engines are gems that should last a very long time with that true chrome liner, I expect my 46nt and 91nx to outlast any of my OS engines that aren't ringed.