None. You should see no bubbles. This is causing you to run lean. I would check the fuel line for a pin hole. Pay close attention to where the fuel line slides onto the tubing at you tank. That is normally where the line is cut. Also be sure that you tank is mounted wrapped in foam. It should not be touching wood. It should have foam isolating it from the planes structure. At higher RPM's the tank will sometime vibrate so much that the fuel foams if not wrapped properly.