Mercury 115 spark plug burned electrode

Shakeynight

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Sep 7, 2020
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I recently picked up a 1993 115 Mercury, I noticed after the last outing it was leaking water around the plug after replace omg the gasket and everything in the cooling system. I also replaced the plugs. I checked them after about an hour of running and all of them have punted a groove in the center of the electrode. I have never seen this before any thoughts to what caused this?
 
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