I would bet your getting some vibration from the tank hitting the firewall opening. I like to make the opening about 1/4" bigger than the stopper. Then put a bead of silicon around the stopper before I install the tank. Then when you push the tank into place the silicon
will form a little cushion around the area. That being said I have a .72 on a Pizzaz that gets small bubbles in the line after a flight. The fuel tubing has a 1/2 loop in it before it goes onto the carb nipple. I can see the bubbles in it after I land. I have well over 150 flights on it like this and it has caused no problems. So is it vibration,rugged flying, tank to tight? Who knows but the bubbles are small and don't seem to effect the engine.


david