I'd like to add that the high needle seems to be not so sensitive, while the low end needle is very sensitive.

The easiest way to match the bisson muffler to the stock one would be to open one tube fully, and plug the other completely. To save time, I compromised both tubes to a point that somewhat equals one open tube. I may be off a little bit, but I won't know till I try some test runs with different settings. I may hack the corner off the fuse and go with the stock muffler to test different props. That will remove the muffler pressure from the equation.