Originally Posted by rick
A thread I was reading on here last week about cold weather starts may explain the bad mpg in cold weather. One reply stated that because the fuel is colder, it is harder to get it to atomize, to become a vapor rather than droplets. Thats why you need to choke or richen the mixture.
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With fuel injection systems you can't do either. The fuel processor takes care of all that stuff for you.
The colder it gets, the denser the air becomes, resulting in a more oxygen-rich content. I would guess that this actually requires less fuel, as it's the oxygen that supports combustion. I think what actually causes poorer gas mileage in low temperatures is a combination of things. The cold air is more dense, so the engine simply has to work harder to push the bike through the air. When it's cold, all the metal parts of the bike are cold, such as wheel bearings, etc., adding to the engine's workload, at least until things warm up. So basically, when it's cold, that engine just has a harder time making things go.
As far as poorer gas mileage in high ambient air temperatures goes, I've never heard of that happening, but it could make sense, as at high temperatures, the ambient air is less dense, therefor contains less oxygen, which would, in turn, require more fuel to sustain proper combustion. But that's just a guess on my part.