When I went to change plugs this spring (as well as last spring) I noticed that the front cylinder plug was a little darker and partially black on one side of the electrode but the other side was almost the proper light brown. Where the rear plug looked perfectly even in color over the whole electrode. Is this common for an EVO with 50K+ miles on it? The bike runs fine and always starts without a problem. I've got a S&S Super E shorty, Screamin Eagle ignition and a dyna coil if that helps.

 

Just the nature of the beast ! Rear cylinder getting more heat from the front cylinder

 

alaskajeff,

I'm kind of interested in the replies you receive. Mine's just the opposite, the rear cylinder is a bit rich and the front is perfect. The Dyno says that the advance curve and jetting on my S&S carb are perfect.

 

If you have a valve seal just starting to go it will leak and "mist" one side of the electrode. This will make it darker. As it gets worse the black will get wet. Or if a valve is starting to leak it can "lean out" one side of the electrode.

 

Yeah, mine was always darker on the rear and with stock ignition, the rear is timed about 2 degrees lower. A true dual exhaust conversion made my rear plug a bit lighter and the ignition I'm running now has it cleaner than the front, but head temps differentials are still typical.

 

I've been told running rich isn't a bad thing. Running lean caused more heat.
Any opinions!

 

John,
I know that you are generally correct with these types of things. New ported SE heads with Cometic Viton seals and new CP pistons and rings with about 1K on them. The rear plug is a bit sooty, but it's not oil residue. Compression and leakdown tests were on the money. Thinking about checking the accelerator pump on the S&S over the weekend to see where it's pointed as the carb was polished and rebuilt at the same time. Might also try replacing the Dyna 2000 module with my spare Crane HI-4 and see what happens there. What do you think??

 

Buddy,
If all was done correctly then I would also check the nozzle and while I was at it I would also re-torque the manifold. Were the SE heads ported aftermarket? Some times a difference in flow or velocity will cause this also. You could try the Crane unit and play with the rear cylinder timing (keep it under two degrees) to see if that helps.