I was told when I purchased the boat Baja 272 that it had a 540cid/485hp motor install with 35 hrs. The motor has the fuel injection off the 502 that was previously in the boat. The guy that did the work had Alantic marine built the motor and he put the injection on him self.
When I go to wot it tacs to about 4900 and when cuts out for about 1 second or 2.
1. What is the best way to check to see the fuel/air?
2. I have heard that I can have computer reflashed ?
3. Alantic marine said they recommend to carb.

I am not planning to race just want to make sure I don't detonate it.
Or what would you do?

That fuel injection setup will easily support that HP. No way I would ditch it for a carb. There are a lot of people on here that can fix/tune it properly. Where are you located?

Does it cutout out for 1or 2 seconds just once or is it repetitive?
I would not just reflash the computer when you don't really know what the problem is. Engine cutting out could be anything from a bad electrical connection / ground to a fuel issue. More trouble shooting is in order.

To answer your questions in order:

1) To view AFR you need to install a wide band O2 sensor in the dry section of the exhaust. Many ways to do this depending on specific manifolds used.

2) If you have a MEFI ECM that came with the Merc 502 EFI it can be tuned or reflashed. Don't do this yet. I doubt it is your problem.

3) Keep the EFI.

Just above Cinci ohio

It does the same thing all the time

Any chance there's a rev limiter

See if you can get Articfriends (OSO longtime resident 502MPI dyno tester / programmer/etc) program it in the water. He's in MI sopmewhere. He will charge you $$$$$ of course.
look up his posts/threads...you'll get the idea.

Website:
Services

Here is his biz card:

Sounds like its hitting the rev limiter to me. Rev limiter feels just like brief stall or engine misfire.
The stock rev limiter on a 502mpi is 5150 rpms. First thing is to verify your tach reading. It could show 4900 on the gauge but really be at 5150rpms.
Who did he say programmed the ECM?? The only way to do it right is either in the boat with an O2 sensor or on the dyno.

If you get a 02 bung installed in the exhaust I could tune it on the water for you, sounds like its hitting rev limiter and if wasn't tuned for other changes I doubt tune is anywhere to close, its a little jaunt from your you to me but others have done it, Smitty

which 502 did you have from the start and what ECM ? engine serial would help for some of the stock parts if they are still installed. Have no idea if it started out a Merc big block or not ?

fuel pressure tests and and inline seal spark checkers can help rule out or in as possible issues. Depending on the ecm - one can scan that as well and or data log it checking for issues