To be clear, air bubbles at the carburetor occur when the clunk line in the tank is cracked or loose, allowing air to enter instead of fuel.

And, if the clunk line is too long, the clunk might squirm around to the top of the tank, where air would enter, rather than fuel.

Air Leaks can also occur outside the tank, at the tank / line connection or at any line connection between the tank and carburetor.

Good luck,
Dave Olson