Just went through some of these same problems with my TT 120. I ran it with Omega 5% and extra castor added on the bench, using the factory muffler, and it would follow the needle valve very well. (Four-cycle rich at maybe 2 or 2 1/2 turns open). Then I put it on my new Aeroworks Edge 540, using a Slimline Pitts style muffler and APC 16X8 prop, 10% Omega. It ran very strong, but could not be richened at all. That leaves me very uncomfortable..... So, I plugged one of the two stingers on the muffler. Now it could be richened, but on this airplane, needing all the power it can provide, the power was off enough to make the airplane somewhat "doggy".

I tapped the backplate and put a Perry P-30 pump (now Conley) on the firewall behind the engine head. Now it runs strong, and can be richened to a four-cycle at 2 turns open. This is the fifth or sixth Perry I am using and they all work well. I think this would solve your problems. And BTW, I don't set the pumps for maximum pressure. They are not critical. Good luck!

Clair Sieverling