I run Red-Line synthetic racing oil mixed at 40:1 in all my gassers - i think this is the "after brake in" ratio they call for in the instructions for the evo 26 too - also, you might want to try different prop - I gain 500 rpm just by changing props....
What muffler are you using? - If it is Bisson muffler, cut off the ends of the down tubes - just enough to open up tubes to their full diameter. By the way, does your engine spits out a lot of oil, making a mess kind like glow engines?