Increase in MPG/K&N

[Fazerider]

From my first post I still a question.
What I want to know is why did they tune the fazer to run rich, there must of been a good reason, so by fitting a K&N are you not "braking" the tuning the factory made.
I've only just changed my filter at 16,000 miles to another OEM one, and didn't notice any difference in performance,
So far I only read darrsi has seen a difference in performance with the K&N filter has anyone else seen a difference?.
My brain cogs are thinking if I saw no difference from a 16000k - 15 year old one to new oem then why would I expect to see a difference from an original to a K&N, I fear that any difference felt is physiological.

I agree, it's psychological (assuming that's what you meant). A filter that is less restrictive won't alter the fuel/air ratio and the amount of work the engine has to do to pull air through the filter is trivial. It will make a difference at the top end of the engine's performance where it will make a couple of extra horsepower available (with a corresponding increase in fuel consumption).
I neglected the air filter on my bike for many years, it probably did about 80,000 miles in that time. There was no detectable change in mpg when I put the new one in.