Hoping someone may be local, need help. I have a 01 envision boat that I put a 95 502 mag efi into. Was having issues after running that it would sound like it was vapor locked. So I replaced fuel filter which was from 2019, oil filter, new oil. Fire it up smelled gas really bad then found that the vts was leaking got a seal kit. Tore apart to fine NO gasket in there at all. Found the diaphragm was varnished so replaced it while I was in there. Run about 20 miles and boar sits for 2 hrs. Went to start it and idling out of the cove it dies. Get towed back..sounds like it's not getting fuel. I know if it sits all night and I go back in am it will fire up. I'm at a loss. Someone said the cool fuel valve is bad but by serial number which is 0F363869. I don't ser one at all and based off of it being on the port side by motor mount I don't ever remember seeing anything there. Again any help or advice would be appreciated. At this point I wanna tear all of it off and put an electric pump with regulator and return line to tank..

At this point I wanna tear all of it off and put an electric pump with regulator and return line to tank..

This is what needs to be done.........95-97 ambient air temp....have you tried raising the hatch while coved up ?

Return to tank is best option for VL
Problem with VST is that will be harder to do but still doable

One think that can be done if it is VL. Have a rag and small item to push in on shrader valve on fuel rail. Place rag over shrader valve on fuel rail and let air fuel mix escape.

Turn key on/off a few times and let air/fuel mix escape

Once no air is visible, try restart

Yes I open the hatch. Where is the Schrader valve? Port or starboard

i would check your fuel pressure first. Make sure regulator and pumps are good. We had similar issue. Turned out being regulator. Problem went away.

Valve is item 13 under the plenum
https://www.mercruiserparts.com/bam/...31796/1614/150

Issue is it never convinentlly happens.

If vapor lock really is your issue, just remove the return line from your fuel filter head and return it to the fuel tank. This is a known, proven solution for the problem.

to do this would I need to get a T for the filler neck and run the return over to that?

That is certainly an option. Some fuel tanks will have an extra bung that isn't being used and it can be returned there as well