Puzzling gas milage

I did not notice this last winter riding. But it is interesting. I do keep track of fuel milage , I know it may be a little strange but thats just me. I have noticed the same thing on both the XJ and XS1100.
All summer I have been getting an average 33mpg on each tank. I put in 3 gallons when the trip odometer gets to 100 miles. Seems Ok to me.
Since the weather is getting colder I can go 115 miles on the same 3 gallons, thats 38mpg and I like that . Is the colder weather really changing my gas milage or is it something else? My dirving habbits remain the same, same distance and speed to work. I can't quite figure out why.
Is the fuel different durring winter?
Will cold air have an effect of fuel milage?
Summer time temps here in NC range from 70 at night to 95 day
Fall/Winter temps so far have been 35 night and 70 day.

 

My bike got very lean when it got cold so I richened the mixture. Went for 35 mpg to about 32 mpg. You may want to see how lean you are running.

I had a thread on fall tuning. I have asked other folks here at work with injection and their mileage has gone down. I assume they are getting richer mixtures.

 

I would second the lean condition. When the air is colder, it is denser, so it contains more oxygen. Normally this will give you a bit more power as well as a more complete combustion. If you are going too lean though, your engine will get too hot and your oil will start to burn. These bikes are normally set up a bit rich to protect the engines, so you might be alright. The easiest way to tell is to pull the spark plugs and look at them. If they are tan you are fine, if they are white, you are too lean.

 

Fuel IS different during the winter, basically there are "summer" and "winter" gasoline blends which differ by region but there are still differences. This explains it: http://www.theoildrum.com/story/2006/9/13/234043/431
Cold air can have an effect on fuel mileage, moreso on computer-controlled fuel injected motors that compensate for the cold by running righer.

 

Mine too went lean once the weather got cold. I could really tell in the morning when the air temps were in the 30's by the exhaust note that she was running lean. I haven't been keeping track of milage lately, but I can hear it and feel it in the throttle.

 

I'll have to look at the plugs this evening. I have never had a problem running rich or lean on the bike. It runs real good , lots of power. I can sometimes supprise newer bikes with how fast I can excelerate. Most HD's are no problem. I embarased a friend on his new 1500 Vulcan, he thought his bike was fast. I showed him, left him like he was standing still.

 

That is a interesting article about gas. I never knew there was a big difference between summer and winter blends.