You guys are comparing apples to oranges.
Everyone rides different, tire pressures, chain wear, dirt density, AIR density, etc etc.
You can't 'tune it for better mileage' and still have any kind of responsiveness, torque or fun for that matter.
You can only do so much to a 275lb 450cc motor to get mileage out of it, and that is to 'cork it up and lean it out'.
The bottom line is that 'real' four stroke dirt bikes (uncorked motors) get between 40 and 30 mpg depending on the bike and rider.
My fully ported and cammed '08 gets about 32 the way I ride it.
If I WANTED to, I could ride it in such a way where I would get 40. I don't want to.
My CRF450R gets 37, because it is lighter, and you use much less throttle.
The AS Racing D37 experts get 14.5 mpg on their 450 during a race!
With me riding the exact same bike (because I am way slower) I would get about 35mpg.
That's it, there's not much more to it than that.
Every single dirt bike has this same issue, it's not a WR issue.
Go to the XR650R forum and see how they deal with 19 mpg! A 4.6 gallon tank!
If you wan't better mileage, cork up the intake and exhaust, and get a Yamaha programming tool and get it dyno'd for JUST ABOVE the Stoichiometric ratio.
That is the ONLY way you are going to get the precise tuning required to get full AF ratio control over the entire rpm.
That's the ONLY way you are going to 'get your mileage back'.
You could also do it with a K&B Air/fuel meter, which requires a bung to be welded into the header.
Then the bike will run like a 1981 Honda XL250, and be pretty much pointless.
Edited by TheKoolAidMadeMeSick, January 09, 2014 - 07:22 PM.