John,

Not angered all!

If you recall you were kind enough to show pics of you adding an additional tank (pony tank) to your airplanes on certain setups which is what I am referring to essentially doubling the fuel capacity. Looking at your setup and plumbing diagrams supplied by RCKen or Minnflyer the muffler pressure would be the same if you have one or two tanks involved. The pressure is supplied to the second (pony) tank to feed the primary fuel cell which in turn supplies the engine.

My point is this is not a big deal in most cases if the setup is sufficiently close to the muffler to provide adequate pressure. Otherwise a pump maybe required depending on the distance and location of the tank(s).

It makes no difference to the engine how large or small the volume of the fuel cell as the muffler back pressure provides X amount of constant pressure depending upon the rpm. The pressure would certainly drop as the volume decreases if it were a closed system like a compressed charge of air as with shallow well water pressure tank system. In that system as the water volume drops so does the pressure until the air volume control senses the allowable drop to start the pump to recharge the system. We don't have that type of setup. We have fairly constant muffler back pressure to provide positive tank pressure as long as the engine is running, even though the pressure chamber or the tank's volume of air increases as burn off occurs.