Spark Plug Color/Residue??? - Harley Davidson Forums: Harley Davidson Motorcycle Forum
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post #1 of 3 (permalink) Old 12-03-2012, 08:27 PM Thread Starter
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Spark Plug Color/Residue???

Running JIMS120 and not having any performance problems, but have some 3500miles on plugs and upon pulling them see that the rear plug has coating of light brown/rust appearance on it. Front plug has only slight light brown/ rust appearance on it. HD Serv. manual describes this color as OK, but curious why difference in coloration?? Spark Plug is HD #6R12. Other markings are FK and what appears to be a 10 stamped in just above the threads. All feedback appreciated.
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post #2 of 3 (permalink) Old 12-03-2012, 09:05 PM
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Front plug is running a little hotter. Normal to have a slight difference between cylinders.

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post #3 of 3 (permalink) Old 12-04-2012, 04:43 AM
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They sound fine... Now if it was black or oily then you woud have issue. Do some research on the Internet as there are some great sites with pics of various conditions etc.

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