I think I found the problem. I cleaned everything up getting ready to do the final assembly on the pump
View attachment 159624 and decided to pull the pump out of a core to compare it to. I found where a 1/4" hole had been drilled and tapped into the port that the filter slips up into. The hole was higher up than the filter neck reaches so it was allowing the pump to pull in air instead of fluid. Any idea what this hole is there for? Should I be looking for any other modifications elsewhere that could relate to this?