1995 502mpi won't start when hot
 

Hello,

I am posting for a buddy of mine as his problem has me baffled. He has a 1995 Checkmate Convincor 303 with twin 502mpi mag engines. The boat runs perfect when first started for the day and will run bang on until for example pulling up to a beach. Shut the boat down for a while, when we went to leave both engines fired up, we idled out of the bay and just about to get up on step lose 1 motor and within seconds lose the second motor.
Everyone is leaning towards vapour lock, but here is the issue. I removed the outlet on the mechanical fuel pumps, crank boat over and no fuel whatsoever coming out... I removed the fuel/water separator off the one motor and it was full, dumped it out and reinstalled, cranked over and nothing. Removed fuel filter again and empty. The anti-siphon valves at the pickups on the tank have been removed (each engine has its own pickup and separate fuel system).
The boat ended up getting towed back to the marina, and by the time we got back the one engine fired back up (this engine has a brand new mech. fuel pump), the other engine was supposedly changed last year with a good used one stated the previous owner...
Anyone have any ideas on what could be going on here, I am lost, I even took the rubber suction line off the fuel/water separator housing and was able to suck fuel up... I am at a loss!!!

the vst screen might be clogged with junk.

I had the outlet off the mechanical fuel pump off though when cranking the boat over and no fuel coming out??? This is before the VST.

Does it have one tank and one tank vent ?

BTW: if you dump the separator, which is before the mechanical fuel pump, it will take a good amt of cranking before it fills up even when everythings working fine. If you remove water seperator again for diagnosing possible vapor lock there, just loosen to break the vacuum and tighten back up,,,do not dump it out.

Yeah we cranked it considerably, I have a 454 mag in my Checkmate and it doesn't take that long to fire back up after the filter has been changed. I removed his fuel fill cap as well to eliminate possible venting issues but all is fine there as well.

the vst screen might be clogged with junk.

Does the other engine start yet ? Let's get that one figured out first if it doesn't.

Hasn't ran it since, this problem has been happening since he bought the boat, but I will get him to put the muffs on and see if it starts!

It sounds like a weak fuel ump combined with vapor lock. Someone posted once about an allen head screw on the vst that can be loosened to vent off the pressure.