RE: Air bubbles in fuel line ?
It can be from different things. You could have small holes in the fuel lines in the tank. The stopper in the end of the tank may not be tight enough and it can draw in air there. Some filters leak air. (not sure if you have one) I use the type of filters that don't come apart and it eliminates air leakage. I would start by replacing the fuel lines in the tank with new fuel tubing and then check the lines or replace the lines that are on the outside of the tank going to the carb and muffler. It could even have a hole in the tank it's self. Sometimes tanks can rub on the fuse framing and wear through or people drill into them when installing hardware. [8D]