2005 F90 hard to start when warm.

[Mingofisher]

Hi all, first time poster long timer lurker. Have a problem with my 2005 F90 efi hoping one of you can guide me in the right direction to the solution. Up until two outings ago motor has been flawless (400 + hours). It starts instantly in the morning, but as the day progresses (from fishing spot to spot) it requires several attempts at the key including shifting the boat into neutral and revving to get it going. Once on, it runs normal. I perform yearly p.m., add stabil regularly, and always top off the fuel tank at days end. Did notice the vacuum line from the fuel pressure regulator to the intake manifold was not plugged in after the first signs of issue…. replugged it but problem continues. Vapor lock?

Thanks in advance.

[boats.net]

Needs to checked with diagnostic computer. Might check the water passages in fuel cooler.