If it ran well at WOT, I'd look elsewhere. I run 15% in mine and it transistions pretty well. Might try more nitro. If it's only the transition, I might even suspect the needles still need a little needlin'. 1/8 to 1/16 of a turn on the low end at a time. Does it smoke at idle, transision or WOT? Do the pinch test and point it at the sky test to see how it reacts at idle. Great engine, even with that infamous carb.