I've got a problem with my Evolution .46NT.
It's installed in a Great Planes Piper J-3 cub Arf.
I orginally attached a Slimline pitts muffler to it, and it worked well, but then started losing rpms.
Because I thought it would look better, I put on a Bison Pitts muffler.
This has restored my rpms, and it sounds better, but when the nose is up, it goes lean and dies; when the nose is low, it goes slobbering rich and dies. 1/2 to 2/3 throttle is fine however.
Seems to me its a fuel delivery problem.
I have a check valve installed on the line going to the carb, and its worked fine before. O-rings on carb, low and hi speed needles are good.
I've flow tested, and pressure tested the entire tank and fuel lines.
Any suggestions?