I'm at 5200' and running 122.5 jet, no snorkle, Uni Filter, 2 Bros pipe, no smog, crankcase mod, and Iridium spark plug. Bike has 1100 miles and runs great. Uses mid-grade pump gas. Pulls across the power band, idles perfectly, starts easily every time. Happy with the performance.

Mystery: Why is this spark plug insulator still white? Running the stock NGK it was a light brown--and that was BEFORE I upjetted to the 122.5. The only variables changed are the bigger jet installed yesterday,which should enrichen the mixture. Right? Any ideas?

 

Hmmm, what pilot size are you running?

 

Stock pilot. What's strange to me is that the only 2 variables that I changed were going to the Iridium plug, and UPjetting from 118 to 122.5. The stock NGK plug was burning properly. I only upjetted just as a precaution to being too lean. If anything, the plug should be darker. Obviously, at 5200' we have an oxygen shortage and typically factory bikes that run fine at sea level are too rich up here and need MORE air. ????????????????????

 

I don't know if Iunderstand your question or we are talking about the same thing..... In a properly running engine the insulator remains white. Unless you are talking about the glazed glossy white that you get from overheating.

 

I mean the center of the plug--the internal ceramic that turns coffee-colored.

 

Here is a photo of a plug pulled from a nice running engine. I am talking about the white insulator that surrounds the "firing" tip. That part should be aflat off white/beige finish. If it is running rich, it will turn flat black. If it is running lean and overheating, it will turn glossy/shiny white.

 

I just re-read your original post and it makes all the sense in the world. The insulator is originally white and as it gets heated repeatedly by the firing and thecombution temperature, it starts to turn off white to beige to maybe even brown as you say. The higher the temperature, the quicker the transition. Theoretically if the engine is properly running the insulator should not get so dark that it's brown.

You said it was brown when you were running the stock jets correct? That means it was running a little hot(lean). Now that you properly jetted it, it is running cooler(richer) hence the insulator getting cooked less and at a slower pace.

 

I have always had it in my head that a light coffee-colored center insulator was indicative of proper fuel/air mixture. And that a white center is symptomatic of a burn that is too lean, one that burns too hot and thus leaves no residue.

I appreciate your answer and admit to being a bit confused. The Iridium plug now in the motor (with about 75 miles at in-town speeds) still looks brand spanking new, from the threads to the center, which is still bright (not glossy) white.

I guess ifI had obsessed this much over selecting my first wife, I would still be a millionaire today.

 

Sorry to hear that.

 

Do you mean to say that you are no longer a "millionaire"??

I'm sorry sir but we are going to have to ask you to leave, no riffraff allowed on this forum.