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Spark Plug Visual Inspection Guide

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This Article is a spark plug inspection guide, I pulled it as backup from a site thats no longer live, I've attached a PDF of the original Page as well. If anyone would like me to make some edits to update it, or add info just drop a reply below :D Thanks!

*EDIT:* Additional Images are 3+ posts down

1) Plug In Good Condition

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A plug in good condition at correct mixtures and timing will show a good efficient burn at the correct temperature and little wear.

2) OverHeating

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Overheating of the spark plug will result in a glazed or glassy finish. Overheating is due to spark plug that is too high in temperature rating for the compression ratio that the motor operates at, Blocked exhaust, muffler or catalytic converter. Also over advanced ignition timing or cooling system too hot.

3) Fouled Spark Plug

post-15320-0-91740800-1340896702.gif

Fouled spark plug indicates a low cylinder compression this leaves unburnt residues on the plug due to a lack of cylinder efficiency such as oil and lead where used. This may lead to running on as the plug heats up and is capable of combustion alone with no spark.

4) Oil Fouled Plugs

post-15320-0-19870300-1340896824.gif

Oil fouled spark plug shown indicates a serious engine oil control problem probably not compression rings but oil control rings or valve guides and seals. This coating is conductive and will cause a misfire. This may be observed as fuel and can be dried off if this is the case you have an ignition fault and the plug is not firing.

5) Heavily Worn out Plugs

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Worn out plugs start to operate less efficiently and thus start to coat with a conductive fuel and engine by product and plug efficiency is diminished and the extra gap places unesecary load on the ignition system.

6) Engine Running Rich

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Too rich is indicated by a powdery black coating, this indicates the plug is firing but far too rich.Check chokes and carb float levels before you go jetting up.

Colour plug chart.pdf

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Are those images scanned from the Haynes manual? Hmm nope just looked. At least not from a recent printing according to the color of those images. The ones in the back of the Haynes manual look better. Recommend scanning those images instead (no I can't do it).

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Hmm, yeah we must be able to find a better copy. . . Interesting, I think I found the original online though

post-15320-0-10281300-1340917942_thumb.j

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Ah much better quality. :) Great article. Matter of fact I was going to look this up myself because I'm having an issue on my plugs. Perfect timing thanks.

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