hi
going to ask you a dumb question OK? have you balanced your prop? what you describe leads me to believe it is a vibration problem or tank not padded enough to avoid bubbling in tank. wrap tank with a couple layers of foam padding, check prop balance and I t hink you said you had replaced all fuel lines. also I had a plane with a thin bulkhead where the motor was mounted which had enough flex to cause enough vibration to cause foaming fuel. epoxyed a 1/8 inch plywood plate to firewall and solved problem.

try these and hope it helps

good luck and happy flying

pt19 flyer