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I just replace the Harley Davidson normal spark plug for the first round since bought the bike. I’m riding 2014 Dyna Street Bob, it has 35000km. Everything is in stock condition except I change the stock air filter to K&N high flow air filter during 30000km but I do not use Harley Davidson Tuner. Attach below is the used spark plug. I do not know how to tell the spak plug condition according to the service manual. Can you tell me how is the spak plug according to the service manual 1-4
1- A wet black and shiny deposit indicates an oil fouled spark plug.
2- A dry fluffy or sooty black deposit indicates an air fuel mixture that is too rich
3- A light brown glassy deposit indicates an overheated sparkplug caused by a lean air fuel mixture.
4- White, yellow, tan or rusty brown powdery deposit indicates balanced combustion.
PS: I apply copper grease to the new plug thread and dielectric grease to the cable boot.
Last edited by jackietan; May 5, 2018 at 06:30 AM.
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Spark Plug
