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1998 502 Magnum MPI

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Old 10-03-2011, 09:57 AM
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Default 1998 502 Magnum MPI

Hey..I'm new to this site and was hoping someone would be able to help me out with a problem I'm having.
I just restored a 87 Scarab 3 inside and out but haven't really done anything to the engines (twin 502 Mag MPI Bravo Gen 6 1998).
I have been using the boat for about two months now and they have been running fine and fast but I'm having a problem now, once I go anywhere and sit for more than an hour they won't start back (just rolls and rolls). If I spray starter fluid in them they will kick off. The last time I went out one would not start at all. It seems to be getting fire and fuel and the only how I can get it started now is spraying LOTS of starter fluid and it then runs fine.
Can anyone give me some pointer on where I should start with this?

Thanks for any info you guys can give!!!
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Old 10-03-2011, 10:12 AM
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These engines have had lots of problems with vapor lock. You could install an electric boost pump at the tank which will normally cure it by pushing fuel through the mechanical pump and up to the main electric pump. If you have VST tanks on your engine then you could remove them and plumb a high pressure electric pump at the tank and fuel pressure regulator that returns fuel to the tank, this will absolutely cure the issue.
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Old 10-03-2011, 10:32 AM
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Originally Posted by Ted G
These engines have had lots of problems with vapor lock. You could install an electric boost pump at the tank which will normally cure it by pushing fuel through the mechanical pump and up to the main electric pump. If you have VST tanks on your engine then you could remove them and plumb a high pressure electric pump at the tank and fuel pressure regulator that returns fuel to the tank, this will absolutely cure the issue.
x2
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Old 10-03-2011, 12:00 PM
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Vapor Lock for sure. The solution is the Merc booster pump kits or run a return line back tot he tank instead of back to the water sep filter.

E10 fuel will also cause them to vapor lock much easier. Opening your hatch and running the blowers after you dock will also help.
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Old 10-03-2011, 01:23 PM
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Get the Mercruiser pump and harness. It will fix the vapor lock problem.

I dealt with this for half the Summer on our (new to us) 502MPI.
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Old 10-03-2011, 05:06 PM
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don't count on that..seem many that it did not cure...re plumbing with return to the tank is the way...
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Old 10-03-2011, 05:31 PM
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x2 return back to tank will fix the problem everytime.
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Old 10-04-2011, 02:44 PM
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Can you remove mech. Pump run a electric pump from gas tank and then run return line to tank
Did they run all return by to seperstor
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Old 10-04-2011, 04:47 PM
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Default 502 prob

fix the problem asap dont just keep using starter fluid, starter fluidiis terrible for motors!
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Old 10-05-2011, 09:15 AM
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Thanks guys! I will take your advise and get back to you and let you know how it came out!
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