I a similar problem air in the fuel line, changed the fuel pump, still air in the line when starting, have been given an idea from a mechanic who has seen lots of these probs. He suggested fitting a non return valve in the fuel line to stop the fuel going back to the tank. It costs about a £5...

The spring clip stays on, but be carefull when pulling it through the hole as ti is quite thin and can easily break (as mine did when I tried to remove the clip)