OK, just got done running it again, I tried playing with the timing but found no RPM increase in the little adjustments I did so I put it back.

I reset the needles to what the book says, then ran it, only get about 6700-6750 on the 20x10 with the first muffler shown in the above links.

So, I tried that other muffler, man is it loud, my ears are ringing, but it picked up a bit of rpm. Right off the bat of starting it it hit 7100 but then slowed to a bit over 6900 and that is the best I can get out of it now.

what do you think? Just need more time?