This is an interesting topic, Iwonder why the Nitro Helicopters don't have foaming issues? Their tanks are hard mounted, they go through gyrations that no fixed wing could possibly do and at G forces that would snap the wings off most planes, and they don't have any foaming issues. They burn the same fuel for the most part that we do in our planes. Granted that they have a small slave tank (wrong term?) but it gets shook up the same as the primary tank. Iwould guess that all of the comercial fuels now have an anti foaming additive. Iknow the Omega and Cool Power does.

My guess is that if you are seeing air bubbles in the line, you have a hole in the supply line, and look all the way back to the clunk. A sharp end on the brass tubing is like a razor blade to the fuel line. I use a stone setting bur, 45 degree taper to clean the IDof hte brass tubing and the a very fine file to knock off the sharp edge on the OD and also to dress the end. After fighting this problem on my first few planes, I found it easier to fix before the first flight on a tank. Also, the bung will sometmes loosen up after a little use and shoud be retightened,

Don