Thanks, appreciate the input.
I've been doing the fast outboard thing for the 20 years and just getting back into a I/o platform.

I would send the injectors out for checking/ cleaning. If all else is good, reinstall and enjoy the many hours that are left.

Yes, good idea. Another quick trick I did after some bad gas a few years ago, I put in 40 gallons and the 2-liter bottle of the Lucas fuel injector cleaner and I could hear a difference, big fan of that stuff now.

Scan the motor, change the impellers because they are difficult when the engines are installed to get at. Do a leakdown test. Have the injectors flowed and cleaned. Send it. I have some friends with 496 HOs. They treat them like on/off systems. Either off or full throttle. They put on 1200 hrs and still going. I have heard of many reaching the 2000hr platform. Oil Changes and maitenance. GOOD LUCK. Remember they are mechanical and anything can fail. 1 hr. or 3000 hr. Just the way it is.

O/K Hrs. on the Computer on the Eng. Hrs. on a clock on the dash. Is Not the same.
I i was to buy a boat and I do Not know the History of these engines, Pull the Exhaust Manifolds and See If you have wanterr in the Exhaust Ports.
If yes Do a VALVE JOB, And Replace the exhaust elbows.

Then at lease you know what you Have, That is only if it passes a Leak Down Test.
Good Luck!!
Anthony

What every one else said, but also add plug wires, and coil packs, or at least test them when ever you change the plugs. I had these in my 47 Wellcraft, and replaced every sensor at least once in 200 hours of my ownership. Previous owner put 400 hard hours on the motors, and they were shot, running a variance of over 50 PSI on a compression test. . now its not always easy to find the correct numbers, but do a full compression and leak down test. All cylinder need to be within 15-20 PSi of each other. Total average pressure tells you a lot about the health of the engine. Run a full proper scan on the ECU. It will tell you tons about your engine health. Be sure a certified Merc person does the scan.

IIf you go all the way to the couplers, then you should change the U-joint too. Be sure to lube all the splines, and be sure you mechanic knows how to properly align the drives to the engine. I now own my own alignment tool an I ask my mechanic to let me test the alignment. It must be perfectly smooth going in or out and it must have full and square contact on the splines. Follow the merc installation process for the couplers and alignment exactly. I own a very heavy boat with way to much power (I replaced the 496HOs), and have had to replace a lot of hard parts. Moving to Arnesons to get away from anything merc. Mercs are great on light boats, not so much on large boats.

One more resource if you want to up your game on the 496 engines, or just want to talk to someone who knows these engines; https://www.raylarengineering.com/ They can walk you through any upgrade pans you have.


I hope this all helps!
-jeff

-j