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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 11-09-2008
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Spark plugs

i was winterizing my gasoline atomic 4 yesterday. i replaced all 4 spark plugs. 2 of them were all coated with a black powder. two of them were coated black but were wet. (oil?) not sure if this means anything. the engine runs fine and didn't have any trouble all summer. i looked in my moyer marine a4 manual but i didn't notice anything about dirty spark plugs. is this something i should be concerned with or is it just normal wear and tear.
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wchevron,
The black powder is carbon residue. This is usually caused by too rich a fuel to air mixture. It is not burning the fuel completely. The wet plugs could be oil from a bad plug miss firing, or a bad ring letting oil thru to plug or a valve sticking. Do you see any smoke when the engine is running? A dark smoke?
Check your oil too, do you see any chocalaty foam? That would be water mixing with the oil. A properly firing plug should look like a cocoa brown color and dry. Hope this helps some
turf
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How long did you run the motor before removing the plugs?

Is the choke opening all the way?

How long on the points, condenser, cap, rotor plugs and plug wires?

Same # and kind of plugs you allways use?

Using oil between oil changes?
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turf
no smoke when the engine is running. oil seems to be okay also. i'll check the a4 manual about adjusting the fuel/air mix.
bandit
i ran the boat all summer on these plugs. plus they were originally in the boat when i purchased it last fall. not sure how long the plugs, cap, etc. have been on. i'm assuming the plugs were the same type. the po had a set of spares onboard which were the same type.

i'll keep an eye on it next year. just wanted to make sure it didn't sound like something catastrophic.
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Put a compression meter on it if you are concerned. They cost about £20 here. If it's not giving trouble, and starting OK, and not burning oil, then I doubt if there is a problem.
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Good compression on an A4 is between 90 and 115. Your head may have a borderline gasket or undertorqued studs (there is a Seacraft manual with the torquing order). "Wet" is ambiguous: An A4 can suck water back into the manifold (wetting the plugs!) if the waterlift muffler is failing or the water supply isn't vented or there is sufficient crud in the exhaust to create back pressure. A 30 year old exhaust is due for a replacement. I have done this and solved a horde of issues thereby.

As noted above, you could have multiple issues there...or just old plugs.

A rich mixture and timing would be my first suspects, as well. Running a tach check (700 RPM is a good idle speed) is helpful. It wouldn't hurt to replace the spark plug wires, either, if they are original.

After you eliminate or adjust timing and mix, consider switching from the recommended Champion RJ-8Cs plugs gapped to .035 to RJ-12C plugs gapped to .040. You'll get a stronger spark and a cleaner burn. My starts have improved quite a bit since I made this a habit, and it's a tip I got from the venerable Atomic 4 Usenet listserv.
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Well, better rich than lean. It won't run lean for long.
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