Joe,

What I notice is that about 2/3 to 3/4 throttle, I get a peak rpm sound when flying level (i.e. full throttle is not the highest power setting). I tried various ground settings and found that ground peak does not equal best in air performance.

I currently use a Bisson Pitts muffler to pressurize the tank. I've had other conversations about when to adjust the needle (full tank or near empty). The latter in my mind means that the extra airspace is "damping" the muffler pressure pulses for a smoother flow of fuel.

Greg.