[bandito2]

Dry cold air is more dense that warm humid air. Perhaps your bike runs a little rich in warm weather and have a more favorable fuel/air ratio going in the cooler, drier winter air giving it just a little boost to HP... (when I flew an ultralight trike in cold air it had more oomph and the wing flew better too in the relatively denser air compared to summertime flying anyway) that is if you use your bike in the more northerly areas where those conditions occur. Might also have different seasonal fuel formulations that might be making a difference. (up here in MI fuel formulations are different between summer and winter... not sure what the exact differences are, but they do occur) Or possibly a combination thereof. Just shootin in the dark, but maybe there is something to it.