Sounds to me like you have a vibration problem, because you say the bubbles show up at full throttle. Make sure the prop is balanced to reduce any excessive vibration. Isnure the tank is wrapped in foam. Just make sure it is not packed too tight, just enough to isolate from the airframe. Last option would be to put an in-line fuel filter between the tank and carb. These filters help remove air bubbles as they hit the screen.

Hope this helps. Nothing worse than an engine going lean due to bubbles.