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Hard Start Problem

H

HZ900

New member
2000 Scarab w/ twin 350 Mag MPI

I've got a hard start problem when the boat warms up. Both engines are experiencing the same issue. Engines start right off when cold, but just turn over when hot. In order to get them to start I have to turn the key on and off numerous times and throttle up all the way when cranking and it might start, along with some backfiring and then it takes a few minutes before it will idle correctly.

What I've tried:
Replaced temp sensor for computer
Swapped in known working IAC, no change so went back to original
Installed Holley in line booster pump (thinking vapor lock and this is a known possible solution) Pump is a 7psi pump.
Changed fuel filters
Filled up at different gas stations, including an ethanol free station.

I'm at a loss here and out of ideas, I really thought the booster pump would work. Any ideas are welcome.
 
Anyone think this could be ignition related? Got to thinking when the boat is warmed up is is smoking just a tad like its running rich. Also already changed the plugs but nothing else on the ignition side.
 
I've got the engine hatch open, with cold hose water running through it in the drive way. I really don't think ventilation is the issue. I run the boat for about 10 minutes and shut it off. Gets to 175*. After that its hard starting.
 
Think I might have found the issue. Fuel pressure is 30psi at best at the end of the rail, tested with two different testers and same result. Even after engines crank and are running. Shouldn't this be ~43 psi? They hold the pressure for a while so I wouldn't think pressure reg, maybe bad pumps?
 
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