There are a few differences, I'd assume, between your bike and mine.
Mine is a 1998 Frankenstein. I believe the motor is an '98'99 EC motor, it
now has a counter balance shaft installed. It is smooooth! Earlier in it's life
someone removed it.
The frame and front forks are the 50mm Marzocchi Magnum that came
on the MC250. When I got it, it was wearing a 19" rear and 21" front.
Why? MX? Don't know.
Now, with the 17"s I changed the gearing to 14/42. I made a huge change
in the way it rides in the road. It is comfortable up to 55 MPH or so.
Anything above that and the powervalve wants to open. Then the bike wants
to "Go Baby, GO!" Like yours it surges above that speed. It either wants to
cruise or it wants to haul azz.
I have several posts here on GGRider. Search "EC250SM" and most of them
should come up. I have also posted several build threads over on
supermotojunkie.com.
Great bike, BTW. Enjoy.
Jeff