I thought I would post this as it may be of use/interest to someone who has changed their airbox recently.

I checked my Co2 settings with a gas analyser over the weekend. I had checked them about six months ago to 3.5% front and 4% rear. I recently changed my air box back to an EVO recently but other than that have done nothing to tthat bike that would have any effect on the air/fuel ratio.

The rear measured at 3.8% but the front read 10.9%.

I can only assume that this was caused by the airbox swap. Might be worth checking if you have recently swapped yours.