balanced fuel mixture?

Is it un-common for one cylinder to burn a little, just a wee bit, richer than the other? I have a buddy that rides a ducati 900ss and he has noticed this on his bike and claims that it is due to the cooling of the front and rear pots and not the fuel mixture.
I looked at the clymer manual and found no way to adjust fuel mixture on the Mikuni CV carbs. What gives, are they that good?
Should I be concerned with this it is only a slight difference and I noticed no performance fault? I only noticed it when swapping in new plugs.

I know that I am replying to my own post again Im not really this lonley.
I showed my plugs to my friend and Mech. Engineer who also by the way raced at the Isle of Mann. He said what I was seeing was a slight difference in oiling of the cylinders and not to worry. The burn of the plugs looked good that I might consider a larger main or raising the needle one notch but that that was a personal preferance and that all is well with the mixture and electrical system.
Has anyone else noticed this difference in there plugs and if so do you know why this might be. Just curious.
Thanks steve

I'll let you know when I change plugs

Very common... The inner cylinders on the inline4's have the same conditions & are routinely compensated for by going slightly larger on the jets or thinner on the needles etc... Truly though the differences in efficiency on the twins are so nominal it's really not worth messing with