I agree. The engine should go lean if the pressure line is taken off and the needle valve isn't adjusted. But I've seen varying results. Some quite dramatic and others not much change.

You don't have any real control over the amount of pressure the muffler produces. Maybe the size of the hole in the tap would make some difference, but I wouldn't think it would be much. And the actual pressure isn't all that high anyway. I don't know that anyone has a real answer to the question. Mostly we just go with what works....I have good luck with the muffler pressure, but then I don't know any better.

Yeah, I think the PF is a real bargain, too. Big (620 sq inches) and light, flies fine on a garden variety motor. OS LA 46 is another good way to go. I saw at least one with a 40 four stroke. Only bugs I've seen are that they are a little vulnerable in high winds and the tricycle landing gear takes some extra care when flying off grass. Not much prop clearance, either. But I've been able to work around those with bigger wheels and 11" props. When you get the takeoff and landing right, they're really pretty. Last night I made up an Al Rabe style jig to assemble my new PF and it looks like it will be among the straighter things I've built. That jig is a great idea.