# Weird substance on spark plug (25 Yamaha)



## William H (Oct 21, 2020)

Good afternoon everyone. I am having a slight problem on my 25 2 stroke Yamaha. I just finnished rebuilding it and putting all news gaskets on it. The bottom cylinder has a blue tinted substance on the plug. It has 130 psi on both cylinders. Is this water intrusion or just a too rich mixture? It seems to run great with no issues of cutting off or anything.


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## William H (Oct 21, 2020)

Also before the rebuild it never had this.


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## BrownDog (Jun 22, 2019)

Blue tinted makes me think oil is somehow involved.

Are you still breaking it back in post rebuild? I would keep running it and see if it improves.


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## William H (Oct 21, 2020)

It isn’t completely broken in but I’ve run it for about 5-6 hours so far. Could the head gasket be a culprit?


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## BrownDog (Jun 22, 2019)

William H said:


> It isn’t completely broken in but I’ve run it for about 5-6 hours so far. Could the head gasket be a culprit?


have these hours been primarily at idle?

Its a 2 stroke with good compression so I'm not too hot on the head gasket idea. I'm leaning towards an unburt oil situation.


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## mwolaver (Feb 6, 2014)

Blue Permatex?


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## Sublime (Oct 9, 2015)

I can give you no more than $300 for it FOB Texas.

Jk, I'm a good taker aparter and put back together guy, but terrible diagnosis skills.


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## William H (Oct 21, 2020)

It was run at less than half throttle for the first 3 hours but now I am running it in the higher rpm ranges close to full throttle.


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## Mako 181 (May 1, 2020)

Double Oil ?


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## State fish rob (Jan 25, 2017)

Maybe a hotter plug.or cooler....


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## Sublime (Oct 9, 2015)

mwolaver said:


> Blue Permatex?



That's where I'm leaning as well, especially since it is described as a "substance"


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## emptysea (Jul 14, 2019)

Sorry to say that looks like a leaking head gasket


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## Loogie (Jul 24, 2019)

That looks like oil and water mixed, you should test it, but a milky substance like that is classic leaking head gasket. It may not be a big leak but it will become big. There should be no substance like that on your plugs.


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## emptysea (Jul 14, 2019)

Take off head and clean well with light or medium scotch bright pad before reinstalling. Torque to specs in appropriate order.


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## William H (Oct 21, 2020)

I did just install a new head gasket about 5 days ago and did torque it to the correct specs. I also cleaned the head and used the finest sand paper I could find to sand it flat. (It didn’t seem warped at all). But I’ll buy a new head gasket again and see if that fixes my problem. I am running it on 50-1 by the way.


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## emptysea (Jul 14, 2019)

when you take it off again get a piece of glass to check if its warped. tolerances are pretty tight with stuff like that


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## William H (Oct 21, 2020)

Ok alright. Could there be any other problem besides the head gasket. Could the base gasket have anything to do with it? I’ve been told when it runs that if there is a leak in the base gasket it can suck water into the bottom cylinder through the exhaust port. (The gasket between the crankcase and midsection)


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## William H (Oct 21, 2020)




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## emptysea (Jul 14, 2019)

the base gasket could be the issue as well. Ina 2 stroke the exhaust and intake are connected so its not that simple a diagnosis.


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## William H (Oct 21, 2020)

(Late response) I ended up replacing the base gasket and am getting the same deal. It seems to run fine and idle great. Should I just run it and see what happens? I am running 32 to one because it’s still in breakin. Or should I just go buy a used power head. Has 130 psi on both. Has about now 8 hours on the rebuild.


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## William H (Oct 21, 2020)

Running quicksilver oil


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## GSSF (May 25, 2013)

I could be break-in cheese on the plug. I've seen worse. For sure.

If she Chuggs strong, keep at it. I say run the heck out of it and see how she holds. You got good compression and all else lines up.... send it!


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