If you really want the engine to run well on 5% nitro, then I would say a carburetor change is in order. You need a smaller intake to keep the need for too much fuel down. When you load the engine up with enough 5% to get it to balance the amount of air it gets, it's just too much fuel for it to burn. It's like putting a cam in an engine that doesn't have the right heads and exhaust system to match it. Power actually improves with the smaller carb because you can get a better needle setting, and fuel draw is also improved. I think Mr Cregger will agree with me on this one.