Rebuild or no?

[Brimikeg]

Good morning everyone,
I have a late model atomic 4 that I recently got running after is sat for a while. From what I understand it was rebuilt in the early 2000's and meticulously cared for by that owner. Then the boat was sold to someone that wanted a diesel so they pulled the motor. I suspect the set it on a pallet at the boat yard and covered it with a tarp and left it there until I picked it up. After some troubleshooting with the cooling system I got it running well with no water intrusion. When the boat is not in gear the motor will rev up as it is supposed to and behaves normally. However when in gear it will not exceed 1500 rpm. It reaches 1500 at about half throttle and stays at 1500 all the way to full throttle. I did a pressure test and got the following results:
1- 0psi
2- 65psi
3- 65psi
4- 75psi
My immediate assumption is that I need to rebuild the engine. I'm going to pull off the head and check to make sure I have no stuck valves or carbon buildup that's preventing them from sealing properly. So my question is, is there anything else I should look at before continuing with a rebuild? I have already pressure tested the water jacket in the block and manifold (and installed a new manifold because that was the root of my previous problem) and everything there checks out. As I am relatively new to this world of atomic 4's I just don't know if I'm missing something obvious that could solve my problem, but in what knowledge I do have of similar engines, I suspect worn piston rings possibly from sitting on the pallet in the boat yard for who knows how long. Any help or advice would be appreciated!

[Dave Neptune]

No rebuild yet! A stuck or sticky valve is probably causing the zero cylinder~~no biggie. The low numbers are not that bad and could easily be sticky rings from sitting or the results of a poor test.

I would add some TCW-3 (synthetic 2 stroke oil) or MMO to fresh fuel at around 100:1 mix.

SPRAY some penetrating oil or lubricant of some sort into each cylinder and let it sit for a day or two. Leave the plugs out and kick her over with the starter once in a while to mix and shake thing up.

Check the centrifugal advance for smooth operation, especially since she has been sitting.

After a few days and/or even some trying to loosen the offending valve with an Allen wrench gently.

Now start her up again and let her run for a bit at various RPM's and stay below 2,000. She may just shake the stuck valve loose and the added oil to the fuel will get in a begin lubricating. Once done let her cool for a few hours and do a compression check.

The compression check should be done with the throttle at full, the choke open, all plugs removed and fully charged batteries.
First do the dry test and record the numbers. Now do a wet test by spraying some oil into the cylinders one at a time and conduct the "wet" test again recording the numbers. Get those numbers back to us for further evaluation.

No need to rebuild unless something is broke or a knocking bearing journal.

Dave Neptune

[joe_db]

^ what he said.
I would bet that nothing is going on other than stuck rings and valves. You can also do a "MMO Tuneup". Get the engine warmed up and start pouring MMO in the carb slowly. When the engine starts to bog down shut her off. Come back in an hour and fire back it back up, once the smoke clears you may have unstuck what needs unsticking At the very least you'll annoy the neighbors with a big cloud of smoke

[Brimikeg]

Sounds good, I've had it running for a while now while trying to figure out what to do with it. Every time I go out to the boat I run it for anywhere from 30mins to an hour to make sure everything is moving properly. I'll give some of these ideas a try and do the tests and post the numbers.

[Brimikeg]

So I went out today and tried first the mmo trick pouring it in the carb, after waiting a while and starting her again it sounded better but still not exceeding 1500-2000 rpm in forward gear. Before leaving the boat I sprayed some penatrating oil into the cylinders, aimed at the valves mainly. I'm letting that sit till tomorrow where I'll give her another start and do the wet and dry compression test. I'll post those results here tomorrow.

[joe_db]

1500 and 2000 are not the same thing. Plenty of boats that are somewhat over-propped or have dirty props don't get much past 2000.
I would try a compression test again soon and see where you are.