Your exhaust temps were higher before, which could have helped to burn off more HC/CO's, i.e., every action causes an equal but opposite reaction.......

Hi Snowtoy...  although I get your point about exhaust temps, "every action causes an equal but opposite reaction" refers to Newton's Laws of Physics regarding motion, not gases.  I think you meant the Law of Gases of Robert Boyle as most often discussed... i.e, doubling the absolute temperature of the air in an engine cylinder will double its volume.  Beyond that, the chemistry of gasoline combustion and AFR inside an engine cylinder gets complex quickly... at least for me.

Gnarls.