115 2+2 Water on #1 spark plug

[botop]

I’m running a 1995 115 2+2 Mercury on an 18ft Astro bass boat. My issue is my #1 spark plug has moisture on it when I pull it and the other 3 plugs look like normal carbon wear. I’m only getting about 38 mph top, but the prop is pitched for a fish and ski boat (19 pitch)

What I’ve done:
New impeller
New lower end gaskets including the prop shaft seal under the impeller since I had some water in the gear oil
Re-tuned the engine per the Seloc. Initially it was idling above 1000 RPM and the book calls for 750-800 RPM. Also adjusted the top 2 carb idle mixtures per the manual. It still runs like a snotty 2+2 at idle and isn’t smooth until a little throttle is pushed in (makes me think #1 isn’t hitting all the time?)
New plugs, checked the ohms on the wires
Re-wired the main power wire since it showed signs of getting hot (stator wire?)
Rebuilt the fuel pump
New fuel and oil lines
Cold compression is 110-112 on all 4 cylinders
Re-torqued the bolts on the cylinder head and the exhaust cover to 18 ft-lb (most of them were 1/8 to ¼ turn loose).
I’ve scope the cylinders and the reed valves; all good (#1 is spotless like its getting some water in)

I’m just curious if there’s anyone has actual experience with the issue. Please don’t tell me to throw random parts at it unless you’ve actually ran into this problem or run a 2+2.

-jt

[JOE54]

blown exhaust plate gasket , been there seen that , also seen cast flaw in top of combustion chamber leak

[botop]

Is the exhaust plate under the cylinder block or over by the water jacket plate on the port side? How terrible is that job?

[JOE54]

port side ,not to bad

[botop]

Thanks. Did you break any bolts? I’ve read that people snap several from corrosion I’m guessing

[JOE54]

yes i did

[botop]

Do I need to use something like high track gasket sealant? The manual doesn’t really say

[JOE54]

not needed

[blackboat]

Like Joe mentioned....Really look close for casting flaws. They can really be tough to find. The motor can be fine for years but corrosion can eventually eat through thin spots deep in the cavities of the castings.

[dave540]

I had the same thing happen on a 1991 Faststrike 150. #1 plug looked brand new and the other 5 looked normal. The engine would run normally until it warmed up. Then it would drop 300 rpm at wot and it sounded like BB,s rattling around in the powerhead. I replaced everything to do with water, seals, gaskets, etc./ Still did it. Rebuilt the powerhead, still did it. I took the powerhead off and disassembled it. I could not find anything obvious. I torqued the heads on the empty block and made a block off plate for the other water jacket. I then screwed a garden hose to the flush on the back and turned the water on. On the #1 cylinder at the bottom where the sleeve contacts the block, every few seconds, a drop of water would roll out. The sleeve wasn't sealing at the bottom of the block. May not be your problem, just relaying my finding.

[botop]

I’ve got the gaskets and it looks like I need to replace about 6 bolts. I guess I’ll start there since if I need to order a new exhaust and water cooling plate they come with gaskets anyways. I managed to not break any bolts but two of them were super corroded and practically missing most of the threads. To me it seems like a 50/50 shot of fixing the problem. I can’t tell off the gasket had any leaks since it tears apart during removal but I definitely had a couple bolts that were cooked in exhaust carbon. I’ll probably use blue loktite on all the bolts to help them seal better and hold back the corrosion some.

[JOE54]

good luck ta ya