While doing some upgrades on the engine I removed the plugs to roll engine for pulling adjustable pushrods and I noticed the rear plug is darker than the front plug.Last year I changed ignition to Dynatek 2k, not sure if this can have anything to do with it.I don't think I could have a tight pushrod, new lifters last year as well. The heads were rebuilt when I did the rest of the motor. Is a dark plug especially in the rear anything to be concerned about? I know the rear generally will run hotter because of lack of air flow.
Ideas?

 

One would think that the rear cylinder runs hotter but I read on this or another forum that a guy checked his cylinders temps with an IR gun and the rear was actually running cooler than the front.
I don't believe he was having problems, he just wanted to see what temps they were running at.
Bottom line, if your bike is running well, I would not sweat the rear plug being darker than the front as long as it is not oil or fuel fouled.

 

In the tuning section of another forum, a documented carb tuning thread with a Wego afr reading system in each 02 sensor recorded different afr's between cylinders and it has been common since the Shovel days so don't sweat it and throttle on

EFI is easy to make the cylinders equal but carbs takes the hidden intellegence of "Rainman" to make carb cylinders fire equal, Nascar head programs is an example of these Einsteins.

 

Don't know if they still do it on EVO's, but on the older engines the timing was retarded slightly on the rear cyl. to let them run cooler. That would also make the rear plug run a little darker. As long as it is just color, and not wet with oil, I would not worry about it at all.

 

yes its just color and seems to run fine so I won't worry about it.