Trouble shooting 502
 

I’ve got a 2000 Merc 502 that will run perfect until we cove out for a couple hours and then when we fire it back up it’ll run for about 15 minutes and then it’ll just fall on it’s face. It never quits running, but it’s almost like a complete loss of power, stumbling, or misfire. Any ideas/help would be greatly appreciated. Boat has new plugs, plug wires, and fuel filter this season.

Check for trouble codes and verify fuel press when its acting up.

Wut he said. ^

I’ve only read about these systems here where vapor lock is the main culprit, but paint delaminating in the cool fuel system is often a problem too. Good luck!

Sounds like a vapor lock issue. Vapor lock usually starts right after a hot restart after sitting for 20mins to 2 hrs, not after 15 mins of running though.
How long does it run crappy?? Does it clear up after a while??

Every time it starts running crappy we take it back to the dock, which luckily has only been a couple miles from the house. We went to shootout a couple weeks ago which is a 25+ mile ride and stayed all day and had zero problems on the way home. It only seems to be when we stop for shorter periods of time.

Vent the hatch while stopped next time you're out and see is it still does it, open the hatch a foot or so and let the heat out

Like I said, sounds like vapor lock. Using E10 fuel will make it vapor lock more easily also.
BTW, All land fuel in MO is E10 unless it specifically states Ethanol Free for some 91-93 octanes.

I’ll try popping the hatch next time we take it out and see what that does. We always buy our gas on the water, so hopefully we aren’t getting E10. Thanks for the help