Merc 40hp 2003 EFI won't start when hot

[beaubm01]

My 2003 motor starts right up and runs great. After shutting down and then trying to start an hour later, it starts, runs for a few seconds then begins to idle very rough and then shut down. If I wait a couple of hours it will start and run fine. I have found that if I remove the bottom of the water seperator and then reinstall it will start immediately 100% of the time without waiting for the cool down. Why would that cure the problem? Does that quickly release pressure on the fuel line? Is this vapor lock? Can this be caused by the fuel pump or the injectors? Any help would be appreciated.

ps...Ive replaced my fuel line with the bulb and the filter in the water seperator

Thanks in advance for the help