EDIT: I didn't see how old this post was and replied right after I read the question quoted below (and I missed all the newer posts). I still think my reply has some value to someone, somewhere, but not necessarily in this thread.
kdx220freak wrote:hmm, well what else could i add to beat him in a race without doing a carb mod or porting? thanks
I normally hate to get into this type of discussion...but since it has already started, I'll try to put this type of question to bed, and hopefully be able to share some (possibly) useful knowledge. So here it is:
There is literally nothing you can reasonably add to a KDX to make it "beat" a modern KX250 in drag race, even if you include porting and the like (I'm assuming by race you mean drag race, if by race you mean top speed, the answer is only slightly different - see below).
The motor in my bike is just about as modified as you can get, including big bore, porting, pipe, reed cage, etc. Even with all that, I still get spanked on acceleration by a friend on a bone stock 2002 KX250. Why do I get spanked? Because the KX250 makes more power, period.
My bike does eventually catch and creep past the 250 at top speed, but that is only by about a couple of miles per hour and after 1/2 to 1 mile of stick-straight road. Chalk my better top speed up to the wide ratio tranny in the KDX...at the speeds we're running, top speed is limited primarily by engine RPM (via gearing), not by aerodynamic drag. Given the opportunity to change gearing, the KX250 would spank my bike on top end as well.
Don't take that "top speed limited by gearing" statement to mean you can make your KDX go 150 MPH with only gearing changes. At some point, not too much faster than the current top speed of our bikes, aerodynamic drag will consume more horsepower than the motor can produce - at that point you can't go any faster - this is terminal velocity. For example, the mighty KX500, all stock other than gearing optimized for top speed, has a terminal velocity of around 110 or 115 MPH - it just doesn't produce enough power to go faster than that. Now consider that power consumed by aerodynamic drag goes up approximately with the cube of speed (i.e. all else the same, to go twice as fast you need eight times the power, to go three times as fast you need 27 times the power, and so on). So, assuming a modified KDX200 produces half as much power as a KX500, this means the terminal velocity of the KDX could be around 87 or 91 MPH with the proper gearing.
I guess this turned into a bit of a physics lesson...I hope it was useful and not just wasted breath (or is that finger skin?).
Now, not to sound harsh, but no more "what can I do to make my cavalier beat a corvette" type questions, please.
We also rode laps on a 1/4 mile turn course we set up in a dry lake bed. I had a much harder time doing this on the KX than the KDX...However, by the time the course got real nasty and tore up...the KX just started to shine. Or maybe I just started getting more comfortable with the ergo difference? After tiring ourselves out, we decided to run some ST back to the trucks. We were on this nice 8" wide tight twisty stuff for about 3 miles until we hit some of the more worn in stuff. The KX worked great in the slow stuff. No stalling today. I'm going to have to go to the dark side with ski. 
The only thing left to do is clean up the jetting a tad (still slightly rich) and finish the kick stand. I'll post photo's of the kick stand when we get it finished.
