There are some excellent ideas above for how a pressure tap could be added to the muffler. While I don't personally like adding a nut on the inside wall of the muffler to retain the tap (Murphy seems to dictate that things that can come loose in mufflers often do..and then end up inside the engine ) I also think the main point may have been missed. The reason K&B doesn't have a pressure tap on the muffler, and the reason they say just to vent the tank to the atmosphere, is that they were DESIGNED to run best that way. having run one of the .28 sportsters, I can attest that even though I too had to TRY some form of pressure boost on the fuel to the carb, the engine just plain was easier to set up with the tank vented to the air.

As for concerns about fuel running out of the tank, all one has to do is to run a line from the vent on the top of the tank, straight down, and out the floor of the plane. When the plane is upright, the vent is above the top of the fuel in the tank...no fuel running out. When the plane is inverted, the END of the vent line is STILL above the fuel in the (inverted) tank, so it still can't run out.

Just my thoughts...

Lee