fuel pressure regulator
 

I have a 2001 Chaparral with twin 350 Mag MPIs. After running for a full day, we stopped at a sand bar for an hour or so, and when I it was time to go, the starboard engine would not start, just crank and stutter, but would not run. As luck would have it, about half way home, it started so now I have a problem I can't really troubleshoot. What I did find though is when the starboard engine primes the fuel system, the pump sounds eratic, whereas the port side is very smooth. I have repaced the fuel pump, fuel filter, swapped relays and ECMs between the motors. I swapped the feeds at the tank as well between the engines. The only thing left is the regulator. Does this even come into play when the engine is priming? Am I barking up the wrong tree if the engine runs fine when it is running? I have not yet checked the fuel pressure, but as I said, it runs fine when it is running. Could it have just been vapour lock? Or would that have affected both engines?
Any ideas would be great