What is this?

[tsubaki]

Was pushing along most of the day around 4000rpms, going about 32mph and consuming about 12gph. Occasionally slowing to idle or no wake speed to look at stuff.
Coming back I seen I was sucking 17gpm at about the same speed and rpm. When I slowed or tried to speed up I realized it was skipping. Got it back to the house and removed the plugs and found this in the #6 cylinder.



Brought the piston all the way to the top and had the same imbedded stuff.

The residue is much like carbon build up, it actually completely covered the electrode of the plug. I picked the plug to what you see in the pictures.
The only color I can describe the build up as, is exactly the same as Anti-Seize which I did use when replacing the thermostats and sensors in August 2007.

Some history of this:
When we got the motor in April 2007 it had 90 psi on all cylinders, except #4 had 89psi. The #6 (yesterday) still reads 90psi.
The water separator was changed yesterday morning just before using the boat.
The motor is fuel mixed at about 50:1 (usually heavy on the oil), with various types of oil, the last one was from Walmart (first time I've used it), I've ran about 30 gallons of premixed fuel with this stuff (counting yesterday). Normally I'll use Quicksilver.
The plug type is Champion L77JC4. Replaced in August 2007. Plugs #1-5 had varying wet oil to burnt (light brown) residue on them.
I'm of the opinion that the lower carb feeding this cylinder is running lean (dirty) and has scorched the piston. I've seen burnt pistons but never on the electrodes of the plugs, even to cause fouling.
I'm planning on cleaning the bottom carb, replacing the plugs, pumping the saddle tanks (10 gallons each) and only using Quicksilver from now on and letting it go till it shows me more problems.
Y'all got any ideas or better suggestions?
And what is this stuff?

[cterrebonne]

looks like detonation. you ran a comp check on that cyl??

[spareparts]

thats part of a piston on your plug, go ahead and pull the head

[macojoe]

Another one bites the dust

[Skools Out]

yep post a pic of that fried motor, that is the top of you piston, were you running premix or oil injection or both? what brand is that motor and yr.

[cterrebonne]

man sorry to see that, sounds toast. we had a couple of carbed engines come into the shop last week that has bitten the dust.

[tsubaki]

Thanks guys!
The motor is the one in the signature, an "84 Evinrude 150 horse, premixed fuel.
The compression is the same as 2 years ago, 90psi.
What's your opinion of cleaning the carbs and changing oil type and seeing how long it might take to finish off the piston, or do you think it will cause even more damage doing that?

[Skools Out]

at least remove that head and clean the stuff out so it won't break loose and make the motor loose a cylinder all together. just clean the head and piston top really well then install back with new gasket run till she dies.

[tsubaki]

I'll plan on doing that, thanks.
I'll put in line with the detrimental repairs list with the other stuff, which is ahead of the regular maintenance stuff and those are ahead of the other projects.
How did that go? God put me on this Earth to complete a certain amount of tasks, at this time I am so far behind that I will never die!

[fishinest]

dont look good maybe try to decarb the motor clean carbs new plugs fresh fuel and see if it helps before tearing apart