So, when I got my 2010 ST1300 in April of this year with 42,000 miles on the clock, it was also getting pretty poor mileage. I think in the very low 30mpg range. I spoke with IgoFar about it and he recommended a t-stat change as well as what to look for on the old t-stat to verify if it was either sticking or opening/coloring properly. He said to look for signs of rubbing on the shaft ( streak of cleaner looking metal). If the streak is ther, the t-stat was binding and perhaps sticking partly open/closed and therefore not letting the engine operate at the right temp. Well, that is exactly what I found when I removed the old t-stat, and after I installed the new one, the mileage went up to mid 40's in the same riding conditions (ambient temperature, windshield position, highway/town driving mix, etc.). A few weeks later, I also did a TB synch/vacuum hose replacement/five way tee clean out which also helped increase mileage a little bit.
Windshield position also has a significant effect on mileage, at least on my bike. The bike gets about five mpg less with the shield all the way up as opposed to all the way down.
