'99 Donzi 33ZX w/502 intermittant starting problem

[mjbtx]

Just picked up a '99 Donzi 33ZX with 502's in it w/approx 100hrs;
A couple weeks ago, the starboard engine would start while out
after running awhile.....got home w/boat on trailer and engine fired
through perfectly. Yesterday, the port engine did the same thing
almost. It cranks through.....fired and idled for approx 4-5 seconds
and died....eventually it started fine. I have currently replaced
fuel/water separators and cleaned flame arrestor. Both engines
have approx 20 psi oil pressure @ idle and approx 40 psi running
up around 3-4000 rpm; Water temps are approx 170-180. Any ideas?

[Griff]

Sounds like a vapor lock problem. Never heard it talked about much on 502's, but several board members had similar problems with 500efi's.

Use the search function and search fro "vapor lock"

[mjbtx]

Any other suggestions?

[robyw1]

Is this an EFI or a Carb engine? Based on the year I assume EFI but I wanted to be sure.

Roby

[mjbtx]

It's a EFI motor.....

[Von Bongo]

All the 502's and 454 efi's can have this problem. It is a vapor lock issue that Merc has a tech bulletin out about. If I remember correctly you are supposed to let it idle a bit before shutting it down and always open the hatch to let the heat escape. Do a search here like Griff said and you will find it.

[mjbtx]

It's been running great now since I let the motors idle for approx 5 minutes
before shutting them down!!! Knock on wood....hope this was the fix.