I havn't checked the MPG on the 883 yet ? but Ls get 55-58 ish.
That's pretty low my friend, stone stock except the air box door deleted and a free flowing exhaust, mine got in the 70s consistently (commuting), better on longer trips when the head was decoked.
As it sits now, averages 36 mpg...
I kinda went a little nuts modding it.