[Deezelweazel]

In the fuel tank there is a fuel line camped to the the return line. This line must reach also to the bottom of the fuel tank. Otherwise it will drain the return line, causing trouble. The fuel injectors release the excess fuel into the return line. If air is in this line it causes trouble.
The injectors need to work against the non pressurized amount of fuel in the fuel return line. If air is in this line you don't have that "backpressure".