My M900Sie is a slightly different animal to your (presumably carburated) M900?
There are also two versions of the M900 with different sized valves so there will be at least 3 versions of mpg figures.
I can get 68mpg from my M900Sie on a long run without sparing the horses, the secret being to stay in the top two gears for as long as possible.
That should return a range of well over 200 miles in theory.
I once went as far as it would go until it ran out and returned 54mpg after going 196 miles. That was doing very short local trips and city runs.
Details of the experiment here.
http://www.ukmonster.co.uk/monster/s...l+light&page=2
Your mpg will be quite low as the new engine beds in and you get used to it and settle into it's rhythm. You should see well over 50mpg I would have thought, once you can hold higher speeds in top for longer, But it's surprising how much it will vary with different use.