Haven't had time to compression test yet. But just ran it today by myself on relatively calm water - again only got to 3800-3900rpm at 40mph. So got it back on the trailer and to home. Took a close look at prop, and itr is a quicksilver mirage 19P. The prop is in good condition but has lots of dry scum on it. I originally thought I had a 23P, but with such a small prop the boat should easily push past 3800 rpm.

I'll do the compression test this weekend and provide update. Hoping it is not major engine troubles.

You are way down on power if you can't spin a 19" prop past 4000 rpms.

Spray some CLR, Snow Bowl or Works on the prop to clean the mineral deposits.

Make sure it has a merc tag on the back of the block with the correct rivets. Seen a similar deal one time guy was fighting a gutless peanut port forever ,finally blew i grabbed old block tore it down ended up being a truck motor with a truck cam .

Maybe a silly question, but currently I have the outdrive off for bimball bearing replacement. My mech will not be here to remove and replace it until next week. In the meantime is it safe for me to do a compression test. Also I have an engine tuner that I want to look at my engine before my other mech shows up for the gimball. Is it safe to start the engine for short increments with the outdrive off.

Thanks

yes it is okay as long as you supply water to the engine,
you said you checked the wires. did you check the cap and rotor? maybe corrosion on contacts.. I have personally had that happen with a 3 month old msd cap.

Haven't checked cap and rotors yet. Not sure really how. I'll youtube it. How do I put water in engine with outdrive off? I assume water is only necessary if I start engine. Just turning it over for compression test needs no water right?

Even a truck peanut port motor should do more than 3900. I know, the PO of my boat put in a parts store truck motor with a very mild truck cam, turned it 4600 for a few years, then a ring land lifted.

You need to check the timing too.

Chris

Just searched some youtube videos on rotor cap and timing. Replacement oif cap and rotor look easy enough so going to do it today with new. The timing looks much more complex. I currently don't have a timing gun and not sure where to see the timing strip on the engine block. Likely going to have my mech do it, but does anyone know what the optimla timing is for a 330hp 454? Based on youtube videos, I need to know the idle curve, 3500rpm curve and type of springs inside the distributor for optimal curve.

Thanks

I would not just throw a cap and rotor on it just to do it. Mercruiser ignition should have 4 screws holding the cap down or spring loaded hooks that attached under the distributor. I would reove the cap flip it upside down and see if there is any moisture or green fuzz on the copper points of the cap.
It was very interesting when this happened to me because you did not feel a miss from a cylinder. It would not accelerate over 4200 rpm and i never thought to look at it because i just changed it.