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Old 06-19-2020, 09:41 PM
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Join Date: Jun 2011
Last Online: Yesterday 09:01 PM
Location: Paraguay
Posts: 35
Default READING SPARK PLUG COLOR

Plug color only indicates how the jetting is for the RPM range you use the most. For most people that is high RPM which means it indicates whether the main jet is too rich or too lean. That is very important but having that correct does not mean your mid throttle jetting is right, or that your jetting off of idle is right, or that your idle jetting is right. I highly recommend a good jetting calculator to know if the jetting is rich or lean between closed and fully open throttle.

Read the color on the first half ground electrode (not at its end) and end of the ceramic insulator. Gray or chocolate brown is the ideal color.

White colored ceramic insulators are caused by
1) too lean a fuel/air mixture
2) too hot a rating for the plug

Gray colored plugs can be caused by
1) use of aviation fuel
2) use of certain synthetic oils (Super M is one of them)

Dark plug color can be caused by
1) excessive amounts of oil added to the gas (mostly with group 1 and 2 oils otherwise known as mineral oils. Go to All About 2 Stroke Engine Oils to see what group oils are in the most popular 2 stroke engine oils)
2) too rich jetting
3) spark plug misfiring possibly due to bad electrical connections or a failing ignition component (CDI, high voltage coil, stator coil)
4) too cold a heat rating for the plug

Be warned about lack of coloration at the side end of the center electrode that is more than a half millimeter. That is caused by too much spark advance or too hot a plug rating. Enough spark retardation allows all of the sides of the metal electrode except for the last half millimeter to have combustion deposits on it.

Cheap gasoline without enough deposit control additives can leave strange deposits on the plug. This is fairly common in 3rd world countries but also happens in 1st world countries. (see https://www.knowyourparts.com/techni...gine-deposits/ )
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Old 06-20-2020, 10:50 AM
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Join Date: Jun 2011
Last Online: Yesterday 09:01 PM
Location: Paraguay
Posts: 35
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Here's the gray color from using synthetic oil (Super M in this case):
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