Doh! My bad. I read your signature wrong. Thought it said 2008 C50.
It is possible that the pick-up for the fuel sending unit/pump is clogged not allowing it to pull from the bottom of the tank. 40mpg is pretty low for these bikes so there is definitely something not right (unless you drag race from every stop light). I've even heard of larger debris getting into a tank when you're not looking (leaf blew into one guy's tank) and it causes issues only when the fuel gets to a certain level.
You can try pulling the tank and dropping the fuel pump to see if it's clogged. Do you have a shop manual yet? If not, time to get one. Easily worth the $$.
Also, give us a download on any mods to your bike, maintenance history, etc.
Good luck.