OK, my 2 cents.
You should be getting around 40 mpg which is pretty normal, give or take 1 or 2 mpg. Here are a few things that can screw up your mileage.
First, do not drive it like a Harley!!! These V4 engines like their RPM's!!! If you lug the engine your mileage will go down! First gear should be up to 20 to 25, 2nd gear up to maybe 35 to 40, 3rd gear maybe around 50, and forget about going into 5th at any speed under 60! To give you an example of just how high these engines are designed to rev up to, the maximum speed for 3rd gear is around 90 MPH!! The power band does not kick in until around 3500 RPM to 6000RPM or more.
Second, make sure you are actually running on all 4 cylinders!! It is a known fact these bikes can and will run surprisingly well on just 3 cylinders!! Starting with a cold engine, use a temperature probe on all 4 exhaust ports and see if they all heat up at the same rate together! If not, you could have a dead cylinder. Also, invest in a spark gap measuring device available at most auto parts place and check each cylinder for a minimum of 0.100" spark. A weak spark will kill your MPG! There could be an issue with your caps as there is a spring, a disc, and a resistive element inside the caps. There is a resistance reading to check.
As stated, make sure your carbs are properly sync'ed but that usually only accounts for a few MPG difference, not generally 10 MPG though. It can happen though, I suppose. Improperly sync'ed carbs will make the bike run a little rough and run hotter than normal.
Lastly, some members have reported that they lost a couple of MPG by switching to K&N filters but not 10 MPG! Yes, any modifications to either the intake or exhaust end can affect economy and may require rejetting. One of the best ways to get a handle on that is by using a colortune plug or a CO sniffer, or by rejetting via the old trial and error method.
Make sure 1 and 2 are checked out first before going to any further extremes...