2008 KX250F - A Great Bike
I have raced motocross since the late 70's, my son is now racing a KX250F, here is what has worked for us..
We were fortunate enough to get this bike from my cousin, it was already modified, here are the mods: Pro Circuit full exhaust system, Race Tech suspension revalve forks and shock High compression piston, not sure of the brand. Not sure if valves were upgraded or not.
The mods that we have added over two seasons are: Renthal bars and kevlar grips; these are my favorite grips, soft, small diameter and long wearing. They cost about twice as much as standard grips, but wear much longer and don't tear, unless you truly wad it up. My son likes the grip donuts, so he doesn't get blisters on his thumbs, any brand will do.
We bought a heavier spring for the shock from a guy at the track that just bought a new one for his 450F, this happened to be one step stiffer than we had and worked perfect for my son as he's a big boy - taller than I am.
We have used many different air filters, but I seem to always come back to Twin Air, however I am trying some new Maxima filters and they seem to be very good. We also have switched to the Maxima spray filter oil and it seems to go farther than my old standby foam filter oil. I'm still a believer in greasing the filter sealing lip with BelRay waterproof grease on every change and try not to ride immediately with a newly oiled filter, either put it on the bike the day/night before or oil the filter and put it in a good ziplock bag, for quick changes at the races/practice.
We live in Florida and practice on some very sandy, dusty, muddy, etc. tracks and I am a stickler about our air filters being perfect, I've never lost a motor to a bad filter and we raced this bike for two complete seasons on one top end, before a head gasket failure and then we replaced the piston/rings.
I change engine oil and filters weekly, the filter brand doesn't seem to be as important as the frequency of change, although I'd be wary of the really cheapo filters. If I get a good deal on oil I'll use the moto specific brands, but have had good success with Castrol. It's really hot down here so mostly 20-50w.
I like good aluminum sprockets and have used many brands with a medium grade chain, these work fine
for the 250F, but if you've got a 450, you might need to pop for an o-ring. I know it weighs a little more and is a bit wider, but unless you get your chains and sprockets for free, it's worth the tiny bit of performance you may give up.
One thing that we use on all our bikes is a holeshot device. I started using these when Ben was on minis and felt that the lowered stance gave him extra confidence on his starts. We have stuck with the button, even though it's not essential. I think it's a good thing to be as close to the ground as possible to control your launch.
Most everything else is standard but we do have some carb mods and ASV levers. Just a note, I had these levers on an old bike and they were well used and getting sloppy and the ASV guys sent me a complete set of bolts and bushings to freshen them up, for free!
Our bike requires higher octane than the pump 93, (high comp. piston) but it does fine with a 50/50 mix of 100 octane race gas and 93 octane from the pump.
Ben is very good at keeping the bike together, he's not a clutch burner or over-revver, but doesn't mind a little bump against the rev limiter, when he's racing hard.
One thing that he struggled with, for a while, was a couple of friends that ALWAYS crash. Since they were friends, they liked to pick gates side by side and run the same classes, but inevitably they would crash and almost always he would be in position to get his bike bent up. A brand new titanium header pipe comes to mind, grrrrr.
We've found that he does best when he concentrates on racing himself and the track, trying to improve his lap times, perfecting technique, etc, instead of thinking about where his friends or other competitors are on the track.
Of course, we still like to ride and race with our buddies, but will take advantage of a practice night/day where we might be one of only a few riders; lots more practice time and a chance for me to get on the track and coach him and to stop and work on sections, you know how it is.
So that's about it, I was a Maico guy, then a Honda guy and now I am really impressed with the Kawasaki, it's been a great bike for us, good luck with yours. - Cheers for the advice Chuck.