Will add to this, what I have remember as we had to fix some of these that would run good and then at any giving moment would not or just shut down, let sit and would run good all over again. Back in late 1998 if I remember correctly was that mercruiser had a bunch of engine serial runs affected by excessive internal ignition module heat and if they got to hot or stayed hot for long periods of time the module could completely fail.

mercruiser came out with a heat sink plate kit which goes on the module to help draw heat away from it and this solved a lot of those sporadic running problem - shutdowns and failures. Just bringing this info about so maybe something to check out or possible module failure to whomever.

All 525 SC with engine serial # runs 0D456000 thru OD763831 used firepower ignition set ups, After those serial runs from Mercruiser came T-bolts ign. Sometimes I know about this marine stuff you just have to believe. LOL

+1
I had this happen on a poker run.. We were in 2' tight chop and when we approached our first stop.. one engine loss rpms for a 1/2 sec and came back, wife asked, "what was that?" I was like, wtf, I don't know?? Then it just killed. Cranked right back up and did it again. This time when I turn the key to prime, it didn't sound off, I went to move the lanyard and it beeped!!

We shoved some paper from my bro n laws cig pack and lasted the day. I changed both kill switches and the initial beep sounded a lot better.... That was my problem! It had missed a lil before but nothing that bad. Easy check!

Check the main power plug to the engine and all grounds associated, coil would be another option

cannon plug and the pins having good solid contacts with none broken nor any corrosion.

I will definitely start with replacing the safety/kill switches. I know I had to adjust the port motor switch a couple of times to make contact so the motor would start up. Then I will start checking everything else. Hopefully I will get to duplicate the conditions here on the rivers and see if it works. Otherwise, I will have to wait till I run in rough water again to test it out. Thanks for all of the inputs. Spoke with my mechanic today and he tends to think it might be a contact or adjustment issue at this point as well.

At least with twins you can roll components between the engines, and eventually you will come across the issue, either by process of elimination or you will find the issue as you are removing/reinstalling parts.

C-Deezy, I saw the boats line under your avatar and thought for a moment you might have been the buyer on my old 240 Sport. But it supposedly went to the Cincinnati area of Ohio.

I could be a kill switch problem which is not adjustable, but I highly doubt it has anything to with the neutral safety switch adjustment.

The problem sounds electrical but it could also be float bowl sticking.
I know n my 525SC Pantera, I launched it nose high a couple times and pulled back on the sticks. The angle would change s much that fuel bowls would flood and stall the engine.
I have also heard of the Merc TB IV add on rev limiters having issues