16 hours since rebuild, lots of blow by with condensation

[electroryan]

Bought a bayliner boat. I am in new Zealand.
Twin small block mercrusier Carb engines, apparently factory rebuilt.
It Had these 2 engines put in 2 years ago, and hour meters have 18 hours.
One engine has a lot of blow by that has lots of moisture in it. The guy that supplied engines 2 years ago said its not uncommon for the engines to have blowby as some of them don’t run stem seals.
I Have just put in new fuel tank, electric fuel pumps, fuel filter, oil filter and 20/50 oil, as well as spark plugs.
Spark plugs are not rusty. I don’t see water in the oil or under the valve cover.
Engine temp and oil pressure is fine. Raw water cooled so can’t check water for oil.

In my mind it can only be coming from 4 places. 1- Condensation 2- Exhaust manifold (unlikely if 2 years old?) 3-intake manifold 4-head gasket

Engine not as smooth sounding as one next to it but sounds fine.
Have added videos.
Lots of condensation at idle speed. Hardly any at 2500rpm, lots at 3500rpm
That knocking noise is from the electric fuel pump.

THANKS A LOT FOR THE HELP

blow by at idle
https://www.youtube.com/watch?v=5_2QtDfuyKU

condensation at idle
https://www.youtube.com/watch?v=HK-H5IC-mOk

2500rpm not much blowby
https://www.youtube.com/watch?v=i6Ifu28Ymjk

3500rpm blowby present again
https://www.youtube.com/watch?v=2hs1PuHYKAo

 

[alldodge]

The motor was either not rebuilt or were poorly rebuilt. No motor should be doing what its doing. Hour meters mean nothing and the plugs are running rich. My thought is the motors where never rebuilt, and this comment has me believing it more so.

The guy that supplied engines 2 years ago said its not uncommon for the engines to have blowby as some of them don’t run stem seals.

Do a compression test

 

[QBhoy]

I’m thinking it’s been rebuilt poorly and or not been run in properly and now a loose engine. That oil won’t help either.