Black electrodes

[techsledder]

So when I was winterizing the Sunsport I found the three rear (port side) spark plugs wear black as night. The rest of the starboard and the front port cylinder plugs were fine and looked great. Anyone have a clue as to why my three others are looking as if they came out of the two-stroke engine and fouled?
FYI, the engine runs like a top. I don’t hear a hesitation or any major knocking or anything of the sort.

[techsledder]

Really? :confused: No one has a clue? Come on...

[JohnnyH]

Valve seals. You ever smell any oil burning?

[techsledder]

Valve seals. You ever smell any oil burning?

Sure, I guess. Do you mean the valve cover seals ir valve seats? It's a big 'ol V-8 351 with 570ish hours on it. Would those seals be going already?

[OUI]

Most likely is valve guides.

[87SunSportMikeyD]

Hey I have that too! Just the rear spark plugs. I always wondered why. Now this fall we developed a noise when you floor the throttle we think it is also valve cover leak. Project #1 for spring.

[jet]

Do you mean they are black on the outside? If so its the valve cover leaking oil down on the spark plugs. the eng leans way back so the oil tends to pour to the rear exposing any old gasket leaks. Mine are due to be replaced also' Anybody know if you can take off the valve cover without removing the exhaust? Jet

[techsledder]

Do you mean they are black on the outside? If so its the valve cover leaking oil down on the spark plugs. the eng leans way back so the oil tends to pour to the rear exposing any old gasket leaks. Mine are due to be replaced also' Anybody know if you can take off the valve cover without removing the exhaust? Jet

Jet, Nope, I am speaking of the part of the plug that's the business end of the plug, inside the cylinder. The only ones not "clean", showing signs of tons of oil, where the 3 rear ones on the port side of the engine. The outside of the plugs are all clean. These plug only have 5-10 hours on them as they were replaced after I bought the boat late this summer.

The insulator tip, the center electrode and the ground electrode were all black. Like you'd see as a fouled plug. I took pictures, I just have to find them on the camera when I get home.

[techsledder]

Notice the the good burn tip...

[techsledder]

...the fouled tipped ones

[michael hunter]

Tech
What brand of plug are you running? Looks like a rich condition. Is that after a day on the lake or after a long period at idle. With out having any running problems I doubt its anything to worry about.

[Irish_Jack]

Hey Tech,
If it was me, I would be taking a peak under the distributor cap and looking for any major carbon tracking(black charcoal-like streaks). If you see any, replace the cap and rotor. The cause is high resistance in the wires. This will make for a cold spark condition allowing for carbon build up. Replace those too along with the plugs. Make sure the engine is running up to temp. Stuck open thermostats will cause cold combustion chambers and fouling...
Cover your basics first... Do a compression test warm--should be 135 to 145 with out any huge variance. Spark plug gap and type are super important... Also make sure you don't have any clogged idle passages in your carb. At an idle there should be no fuel bubbling out of the venturi spouts on the primary barrels. These common problems usually won't cause noticeable misfire until they get really bad. If you have any questions let me know...:cool: