Lets try a Hyosung GT250
 

Picked up a GT250 last weekend, 250cc v-twin, air cooled w/oil cooler. The bike has just over 5k miles and been wrecked twice, got it and some extra parts for $500. Just rode 153 interstate miles for a rough base, 72.9 mpg @ 65 -70 mph(gps). I will start this weekend with gearing changes and try to retro-fit the bodywork from the earlier 125cc Ninja project.

Sounds good.

Let's hope the sprockets are current sizes ...

Greenjoe, Great! Sounds like it has lots of potential. Please Keep us posted with your progress.
all the best, Vic

Changed the the gearing from 15/46 to 15/38 with a modified yfz450 sprocket & dropped the cruising rpm from 7900 @ 70mph(gps) to 6600 @ same speed. Also lowered the bike 1 inch in the front & 1 1/4 in the rear, stiffened the shock, changed handlebars, and a few other minor mods. Trying to put on a few miles to see a change in fe from the gearing. This thing really need some aero mods, I feel like a parachute riding it.

Can't beat the price.

Put on another 150 miles this week and ended up with a disappointing 61.9mpg. I think a big part of that could be from lowering the bike, it now stands alot straighter when on the sidestand, allowing more fuel in the tank before it gets to the filler neck. Also made a 16t front sprocket & will try it with 38t rear.

The best way to get super accurate fill ups is to use the same pump everytime and stand over the bike to keep it level and rock it once in a while as you get near the top. Find a part of the fill plate inside the filler neck that you can see and fill until the fuel just breaks tension and washes over it as you rock.

The last 3 times I filled the TU250X I got 2.36,2.37 and 2.38 gallons. Within .02 gallons difference. I hold it vertical and fill until the gas just touches all of the bottom of the neck. Less than 2.5 MPG difference between the two tanks I have measured. The third tank is full waiting for this week beginning Monday, weather permitting. $8.14, $8.17 and $8.32, price went up this week.

regards
Mech

I'm just leary on filling all the way up that way, afraid I'll lose some out the overflow when I put it back on the stand to go in and pay. Maybe a centerstand would remidy this? Thanks for the advice!

Coincidentally, I also modded my 07' gt250r following in the footsteps of L&S/ Allen and plan on riding the Barstow race later this year. I haven't test rode it enough to get an mpg reading yet. Still need to find a cheap source for aluminum sheets.

How did you mod the handlebars? Still using the same clamps? If not I am interested. I plan on converting the clip-ons to stock to make it easier to travel long distances.

The biggest obstacle with this bike is to make an aerodynamic front end, but at the same time keep the inverted forks clean.
How did you lower the front end? Change internal fork spring size?
If you fill up after 200+ miles the fill up error will be miniscule.
Good luck. Keep us updated.