No luck posting this over on the engine related forum so I thought I would give it a try here. I would like to get some advise from somebody with more knowledge than me on the subject of reading plugs. Is my bike running lean, rich or ok? These photos were taken after 18000 miles. Plug on left is front cylinder. Bike is an 09 FLHT running better than ever. Thank You

 

If that's 18,000 miles on the plugs, they look good to me. Plugs are so cheap I'd change them at 5 or 10,000 miles.

 

They look to me like.........................Very good ! The bottom electrode is not worn, the top electrode has white fluffy deposits ( very good sign of balanced combustion ) and the insulator is not shiny or cracked or deposits on it. Put new ones in anyway, unless your conducting an experiment. Your just show'in off !!!! ya banna....

 

Doesn't the manual say replace after 100000 miles? oh no that's Chevy.

 

At a 100,000 miles you replace the Chevy.

 

You have a V-10 on your Harley????!!!!

 

plugs look fine....the light ash is just reflecting your "Harley designed" lean mixture.

typically, the front plugs are darker than the rear ones due to the difference in actual cylinder operating temps, the rear is hotter.

 

Is it just the lighting, or does that last set look blistery hot from running too lean? The others look fine, so if the last set are the same plugs as the others, then it must be the lighting.

 

All 5 pictures are the same plugs. Not real good pictures of the ceramic insulator. I am right now reading this article, http://www.centuryperformance.com/spark-plug-tech and hopfully learn a little more on the subject. Thanks everybody for your help.

 

Your bike is running fine, those plugs are also a testament as to why they don't have to be changed every other month as some might suggest. In 18,000 miles the center electrode is barely worn, and for the plugs to look the way they do, you have no worries.