Very often, my electric fuel boost pump (injected engine) will not develop
pressure when it is switched on prior to engine start.  It runs but it sounds
like it is not pulling on fuel, but rather air (lost prime?).  If I engage the
starter for a second, stop, then try the boost pump, it will begin to draw
fuel and develop pressure.  My fuel line is mostly per plans:  the line exits
the header tank, goes through the shut off valve then to the fuel filter
located on the inside firewall at the level of the bottom of the header tank.
Then the line goes down the firewall to the pump (mounted per the service
bulletin in the vertical orientation), then further down into the gascolator
and on to the engine fuel pump.

Any ideas what is happening here?  How might I fix it?

Regards,
Ed de Chazal