Re: omc fuel pump
In some pumps, mounting it upside down puts the outlet check valve at the bottom of the pumping chamber. That means that an air bubble can collect above the level of the check valve, which is commonly called "vapor lock". Mounting it right side up puts the outlet at the top of the chamber so the air is expelled before the fuel rises to the outlet, purging the pump and keeping it purged as it runs.
OK, ok, I know there are pumps out there that are running upside down. But if they are giving hard to diagnose fuel shortage problems, don't ignore the facts.
