OK, the fluid is new, pumps were sitting for a bit before I put them on, only thing I didn't rule out was checking pick up, I blew in line had bubbles, but could still be a bad pick up, I think its fuel pump though, was fine then out of nowhere it was dropping pressure, was not rough out, filters good and clean/new lines not deteriorating, so I am looking at pump

There was a thread about the company that makes the mechanical fuel pumps for Merc. I believe the company is Aeromotive and there was a pic of the Aeromotive pump in the thread and their retail was $65 versus Mercs $115+ on line. The new style pumps have a curved vent tube. I just went thru this. I ordered 2 Mercs from BAM and it turned out one had low pressure out of the box, had it replaced under warranty. PIA but at least I learned something for the future about the o.e. supplier and saving a few $. I searched for you but couldn't find the thread.

I will look for that .... thx

You could pull it off and take the bottom off and check the diaphragm. Could have deteriorated from sitting if the boat sat. Similar issues we just had on a scarab. Over 3500 one motor would lose fuel pressure. Dry rotted diaphragm was the culprit. Good luck

That was the info I was going to offer up to ya Tim. The way you run that boat you should change it out every other weekend......

you saying I run it hard???? haha

The diaphragm deteriorates, so replacing the valves doesn't always fix the problem. I've looked at replacing parts from other pumps and the issue always comes down to how to replace the diaphragm. I just buy a new Merc pump and replace the whole thing, it's not worth the risk. I also added a fuel pressure gauge to keep an eye on it.

I do have fuel pressure gauge so that helps lol

Can you guys post a pic of your fuel pressure gauge placement if its direct on engine or where you placed your fuel pressure gauge sender? I want to put fuel and oil pressure gauges directly on the engine for simple checks with the hatch open. I had problems figuring out issues with fuel delivery and oil pressure sender this year and if I had mechanical gauges I would have not been so frustrated. I have 525s if that makes a difference

Mine is on fuel rail, I am adding pressure gauges in dash this winter though also...