Hard Starting

[Clydesvx]

I recently had a used engine installed in my '92. Runs good, sounds good, but doesn't like to start cold. The mechanic 'THE SUBARU GURU' from Lancaster Pa. had an engine vac and used it. It worked fine for him.
When she sits for over 20 minutes she cranks for a while without starting. When she cranks a second time she hesitates and then kicks over. In either one of these situations if I hit the gas she will start.
Here's another strange one...If I turn the key off then back to start between crankings I hear gurgling in the trunk.
Is there a valve in the fuel pump that might be sticking allowing gas to flow back to the tank instead of leaving the fuel system pressurized?
Here another anomaly....If I stick a bottle of 'RED LINE FUEL INJECTOR CLEANER' in the tank she starts fine until I get below 1/4 tank.
Any suggestions or abuse will be appreciated.
CLYDE