Yeah better lubrication - you are fighting a loosing battle unless you enclose the thing in an aero body. Bikes are not built to get high gas mileage - now you start to see the impact of aerodynamics vs weight - lighter is not the issue most of the time only air drag.
I noticed that it was idling at high speed since coming back from the dealer, and wondered whether the carb might need adjustment. So, I found the O/M manual, and adjusted the mixture screw first. I closed it about 1/3 of a turn, leaning out the mixture, but the4 bike seemed to idle even faster after that. So, I turned the idle screw to bring the speed down to a more comfy level.
It sounds like you are adjusting the air screw to controle your idel speed, and that would explane your poor mileage to a point, how you adjust idel speed on most motorcycles is you slow your idle, with the idle adjustment screw, untill it's at a reasonable leavle, then you adjust the air screw untill the engine is running smoothest, normaly it will speed up a bit, after adjusting the air screw so it's idling at it's peek, re-adjust the idle screw untill it's idleing at the proper speed, tweek the air screw one more time, 1/16th or so of a turn either way to make sure it's correct, and you should be all set!
it sounds like you are useing your air screw to controle idle, and if that is the case, you are affecting the fuel/air mix, and making the engine slow down my either making it to rich, or to lean, and that is both wastful, and hard on the engine.
I rode small motorcycles in England back in the 60's and 70's,and got great mileage because they were small....Here in North America,we ride 650's and expect great mileage,and that isn't going to happen...I get 50 mpg with mine,and its great,I don't expect anything better,unless I ride it slowly......sorry,the reason I ride the bike is the fun...and the speed...I can get 50mpg and still blow the doors off everyone on 4 wheels.This has merit all by itself...lol
I think the gearing probably has a lot to do with it. Remember, on an enduro they are geared for comparitively low speed use.
If you found a 650 machine primarily meant for the street I think you would see better mileage.
Motorcycle mileage is funny though, very sensitive. I have a 1700cc machine and regularly return tanks at about 48mpg. I put my wife on the back and get about 53. I must just have a tamer right hand with a passenger.
Ninja 650r yeilds about 55-62mpg from what I have read. My ninja 250r the lowest I have seen is 76mpg. But my commute is mostly flat @ 55mph. So If I were to have a 650R I would prob pull 60mpg out of it also.