Misfires/ no fires will cause exhaust water reversion.

Those plugs are not only real cold but also non resistor.

BTW: What kind of ignition and what inital and total timing ...since we are discussing things.

Okay...back to the carbs...Any chance a piece of gasket remained in a fuel bowl or you installed a wrong meter body gasket or a jet fell out ? lol

Do all 8 plugs appear to be "steam cleaned" to the same degree? If so, I would take a fuel sample before messing with anything else. How long was it in storage? Fuel stabilizer used? Have you added fresh fuel? Replace fuel/water separator lately? If you're running ethanol laced gas like most of us, that stuff attracts water like a magnet.
The fact that you have 2 fuel tanks and I assume each eng feeds from it's own tank makes me more suspicious.

I pulled 5 plugs at random, 3 from the port side port motor and 2 from the starboard side port motor. All appeared to be too clean. To confirm any suspicion, I pulled one from the starboard motor, and it looked rich but definitely firing.

Im going to pull all the plugs this weekend and do a compression test, but I assume all 8 will look clean at this point.

As for storage, it went in in October and came out earlier this month. It went in with low fuel left in the tanks and was winterized and stabil was added. Prior to going out on the water, I filled up both tanks with 93 (~100 gallons each)., so if there was any water/condensation, Im assuming it would be very diluted. Plus, the boat fired up on both motors, on the hose, with no issues after I swapped the jets and plugs on the old remaining fuel. Both idled and ran fine. It ran fine all day on the water until I came into the marina at idle, then it was obvious something was off with the port motor.

I'm not liking the bubbles/water coming out of the port motor. I'm trying to understand the logic in that or why that is.

Here's a pic as I just left the ramp;

Sounds like you got the fuel covered. I've seen single or even multiple cyls get steam cleaned when an intake or head gasket leaks but hard to imagine how all 8 could look the same.

Did you come off plane fast and take some water up the tail pipes? seen it happen numerous times...just a thought??

Update: Went down to the boat

Brief synopsis/symptoms: Compression is 158-160 all cylinders. No water/milkshake on dipstick, but precipitation/water on valve cover oil fill cap. Second plugs in (on both sides of motor) appear to have more water drops than others. Other plugs starting to actually have some color to them, but still not like starboard motor plugs. Port motor does NOT get past 130 degrees, no matter how long I idle/rev. Starboard motor locks in ~150. Oil Pressure is good. A lot of tiny little bubbles coming out of port motor exhaust when silent choice on. Vacuum is all over the place even though "idle" seems steady rpm. Distributor cap and rotor appear very clean and excellent shape.

Pics of plugs in order from front to back on port side:









Dip Stick:


Port motor fill cap:



Port motor/starboard side, 2nd bank from front plug:



General gauge info:


Videos:


High Idle/Silent Choice ON

Both Motors on, turn of starboard motor ~30 second mark

Silent Choice Off

Vacuum Gauge