fuel economy taking a hit

[SHUMBA]

Yup, ethanol does have the same energy or BTU's (British Thermal Units) that of Gasoline.
(Diesel fuel has more as does jet fuel, just don't use these).
Generally speaking, premium fuel does not have ethanol, but ask the seller or contact the company selling the fuel.
The Tenere (my Tenere, no mods) calls for a minimum of 91 octane, or premium gas.
SHUMBA

I re read my answer/input and noticed a word missing.
So ethanol DOES NOT HAVE THE SAME BTU's read energy as gasoline. Sorry about that
I will add that excessive amounts of ethanol can be detrimental to many Gasoline engines. Please do not use E-85 in your S-ten.
SHUMBA

 

[SHUMBA]

Apparently there is a little more to 'winter gas' than I thought. All 48 lower US states switch to 'winter gas' on Sept 15th. It's apparently cheaper to produce, which, along with lower demand, causes prices to drop.

From a Google search -

The difference between summer- and winter-blend gasoline involves the Reid Vapor Pressure (RVP) of the fuel. ... The US Environmental Protection Agency (EPA) says conventional summer-blend gasoline contains 1.7 percent more energy than winter-blend gas, which is one reason why gas mileage is slightly better in the summer.

We definitely notice this up here in Canada. My SUV (turbo charged) burns 91 Octane or premium and uses more fuel per kilometer or mile down your way.
In addition starts and warm-ups consume additional fuel.
So, ethanol, cold weather = denser air = more fuel = more money.
SHUMBA

 

[SHUMBA]

My mileage has just Recently taken the drop. If its winter gas. It should have shown up before now. I've had this bike 5 years and it hasn't ever done this before. 38 mpg sux

Plugs, air filter???

 

[Tenman]

plugs and filter look new. 9000 miles on plugs. Might changem anyway. All the rubber parts look good.

 

[SHUMBA]

plugs and filter look new. 9000 miles on plugs. Might changem anyway. All the rubber parts look good.

Plugs must be iridium's. So not likely the reason for an increase in fuel consumption
Depending upon your riding conditions I mentioned air filter. Now, how about your riding habits, R U getting frisky with your right hand???
Roll it on, she sucks the gas.
Changed tyres recently? Knobbies create an increase to rolling resistance thus resulting in more power (gas) required.
Many factors at play here.
SHUMBA

 

[Tenman]

I ride the same roads at the same lazy speed. Mitas E07 forever for me.

 

[SHUMBA]

Well, all I can say is other than a bird or something restricting the intake airflow or some other form of friction (caliper on a brake dragging).
Have you changed fuel octane or where you purchase your fuel??
SHUMBA