Loucarisma,
If you haven't changed your intake/air box, you are pig rich. Whoever "tuned" the fuel mapping obviously just cranked it up with no regard to proper mixture and didn't test on a dyno with a "sniffer".
1. The intake restriction on the 900 isn't the filter, it's the intake tube to the airbox.
2. A K&N filter does nothing on the 900. K&N has stated this and it's one reason they took so long to start making one for this model.
3. K&N filters do nothing for 99.999% of vehicles anyway. Stock filters are simply not restrictive. Engineers do know what they're doing, and modifying intakes usually ends up in a drop in torque if anything from disrupting the "ram-tuning" resonance. K&Ns do, however, pass about 45x more dirt and larger particles as well.
You should be getting at least 40 mpg even with pipes and hard riding. I have pipes, stock intake, and have used stock and K&N filters. Same power and mpg with both filters. I get low 40s with a headwind on the interstate (70-75) and as good as 60 with a tailwind or drafting at 65. Overdrive pulleys will help a bit. My windshield drags the mpg down a bit.
My best was 67 on one fill (so realistically probably like 62-64) going about 60-63 with a 20mph tailwind and drafting a semi that had skirts and a trailer tail. These are long rides, 3.5-4 gal fills so pretty accurate. I've even calculated my exact trip/odo error to correct my mpg calcs.