JETS-R-US: HOW TO READ SPARK PLUGS

How do I "read" the color of a spark plug? Look at the firing tip of your spark plug while paying close attention to the condition and color of the ceramic insulator and the metal electrode. Observe the color first. Light tan or gray deposits are normal, and an indication that everything is working well. If everything is very white with glazed deposits on the insulator tip, a too lean fuel mixture is likely (or the spark plug is too hot for the engine, or at least for the conditions for which it was used). If black sooty deposits are present, a too rich fuel mixture is likely ( or the spark plugs' heat range may be too cold for the application). Shiny black or oily deposits are an indication of bad oil seals and/or piston rings, and are not an indication that the spark plugs are at fault.

Now I understand what the colors mean but how do I check the plug ? The following applies to ATV's streetbikes, dirtbikes etc. f you cannot perform this safely then use a dyno at your local speed shop. Use a fresh plug and clean air filter. This works best in top gear or an upper gear on a slight uphill area. After running the engine at full throttle do the following at the same time: pull in the clutch and stop the engine. DO NOT let the engine idle and DO NOT let the clutch out until the vehicle has come to a stop. Remove the spark plug and examine the color. White is lean and black is rich.

The plug shown in the middle is the correct color

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