There is one method to absolutely eliminate foaming and unporting without the need to resort to a sealed vent pump system such as used on YS engines. That is a bubbleless tank system by either Tetra or Jett without a clunk. Foam is impossible to form and foam padding is not used. One additional advantage is its not neccessary to have the tank close behind the firewall, they will reliably deliver fuel at distances up to 7 or 8 eight inchs from the engine. It does require a syringe tanker for fueling like this: http://www.darrolcady.com/Jett_Produ...t_products.htm

Many early flights of my Quad Cadet with standard tanks would tend to lose outboard engines during some manuvers such as loops, rolls and variations. That is now a very rare occurance with the substitution of bubbless tanks.

John