TxGoat wrote:
Gasoline can "boil" at fairly low temperatures when it is subjected to vacuum. That can cause bubbles in fuel lines and half-full filter bowls. It looks like an air leak situation but it is more like what happens if you try to drink warm beer through a straw. Warm to hot weather usually aggravates the situation. Gasoline sold today is designed to be held under low pressure in the gas tank, and forced up to the engine under higher pressure. The positive pressure prevents bubbles from forming, and the higher pressure in the underhood fuel plumbing keeps the gasoline from boiling. Any restriction on the suction side of a conventional fuel system can cause bubbles, especially in warmer weather or where excess heat from any source is present.