Gas Mileage

[Stub]

Hey Mike,
Great forum. I read it daily and have learned a lot.
My question. Have a 103cu in. Have 10,000 miles on it in the last 12 months. Have always got 40 to 45 mpg on average until about late October. Mileage has dropped to around 35 on average. Has the gas been reformulated this winter. Fill up 9 out of 10 times at the Chevron next to Latus. Have read this can happen in cars. Just want to know if it might be something to worry about.
Thanks

[BLB350]

Has it been cold in Portland like everywhere else in the West? I don't know if you have a temperature sensor on your model (I'll bet Mike knows!), but if you do, perhaps the ECM enrichens the fuel curve due to the lower ambient temperatures? This would lead to lower mileage. I would guess that this is as it should be, not a problem. :)

[Mike]

Yep, BLB350 is correct (thank you for the input). The IAT sensor works with the Cylinder head temp sensor (and TPS) to try and determine air density and then fuel accordingly (speed density system). In cold temps two things can happen 1; the motor never really gets out of "cold start enrichement" and 2; the bikes are often not riden far enough to get warm enough to also go to full lean. Other things like oil being colder can drag the motor down (trans and primary), even cold tires can have an affect. Last, the sensors can only approximate actual conditions and can vary from bike-to-bike. They are only really accurate at specific calibration set points. Yours may be slightly shifted to the rich side when run in colder climates.
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Mike