ORIGINAL: beachbrada
Our staff commonly uses 30% heli fuel in Saito engines, as it not only gives better top-end performance but it runs smoother, gives a better transition, and runs cooler. So maybe you're not running a high enough nitro %.
I have put the OS "F" plug in the engine, no change. I did break it in with 30% and flew it with 30% for a gallon or two but didn't see much if any difference. Trouble is that 30% is so expensive. But I'm going to the hobby shop tomorrow, I might buy another gallon and give it a try. The engine runs great right now, nice slow smooth idle, smooth transition, about 10k top end. All is fine except for the wicked shaking about about 5200 rpm. Even when clamped down hard on the test bench you can see "two muffler ends" at that rpm. Thanks for the suggestion tho, I'm trying most everything suggested. Just adjusted the valves (3rd time) for a tighter fit, tried a heavy Higley prop nut for more mass, different prop (upteenth time) different fuel (four stroke) and a couple of other small things.
New bearings on order. New bearings in a new engine... sigh.