Start from the tank and work
to the engine. I had a issue wit the pick up tube in the tank that had a soldered elbow
that had a pin hole. No issues when the tank was full. As soon as I got to around 3/4 it would suck air. You also have the round valve that you can crack open and it will bleed itself when you turn the pump on. You can also just leave it open and it will continue to bleed the system.