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Old 07-25-2013, 11:36 AM
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Reading spark plugs (dry fouling?)

Getting ready to sell one of my boats (the one I did the carb/fuel system work on that I was posting in another thread). I figured I'd do a compression check as a courtesy to any potential buyer. I took all of the spark plugs out, and 6 of the 8 were dark in color (like carbon), with no heavy deposits. The other 2 looked to be 'normal'. The plugs don't seem too old, the gaps seem ok. The engine runs fine. We do a lot of idling (while waiting for a skier to get gear on, for instance). Sometimes it seems like the engine idles a little rough, but it clears out fine with no issues.

On an NGK chart, they show a dark plug that looks similar to my 6. They state 'dry fouling'. Not sure why only 6 would show it, as it's an older engine, with all cylinders fed by a 650 Holley.

I'm kinda curious what that dark plug color might mean. Anyone know?

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Old 07-25-2013, 12:52 PM
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The excessive idling will do it, especially if the idle circuit is 'fat'. I wouldn't worry too much about it as long as it cleans up after running. If you're not already doing so, using an extended tip plug may help. You could try a heat range hotter plug, but don't do this if the color is good when you're not idling a lot. A plug chop after a WOT run will help here.
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