With the right jets and not kicking the snot out of the machine, you can get 17 mpg. the only trouble I had was one of the shafts in the idler wheels. It had spacers that were about .060 to short, and this let the bearings spin and eat the shaft. (Made my own spacers and now no problems)

It most likely has 6.5 in front and 8.5 in rear, and they made the improvement in 1997 model year.

The biggest difference is when the power is made in the valved engine, the old 500 had to make power high up the rpm range. the new valved 500 is able to make its power down lower which in turn lets the clutching be changed so that you get both low end and top end performance improvements. Its quiet...