RE: MT-57 help - please!
Since my original post I've gone through everything. I removed the canister and ran with just the muffler. That helped. Then I went back to the canister tried playing with the length of the header and found that by shortening it (tuning it in effect) I have gained a bit more RPM. I'm now in the 6,600RPM range on the ground.
I've also checked the timing and although it isn't an exact science to measure, it seems to be in the range you mentioned. I experimented with moving it just a bit, but ended moving it back as it ran best in it's original position.
I have been running it pretty lean all along and it's had over 2 gallons through it now, so the break-in should be finished. I've switched to the 50-1 mix, and on a whim I also switched from 87 to 89 octane. In doing that I lost about 150 rpm, so I'm going back to the 87 octane after this gallon is used up.
The one thing that is really puzzling in this is the high-speed needle. Everything I've read says to creep up on this by small adjustments. I can crank the needle all the way in, most of the way out, or most anywhere in between and little difference is made on the top end. It does change the transition from mid-range to high, but that's about it.
I'm wondering if it's more of a carb problem.