Modified 2008 Kawasaki KX250F
Taking the winning bike from DR's 250F motocross shootout and modifying it borders on silly. After all, the bike beat everything in its class according to our staff and elite squadron of test pilots (see February 2007 issue). The box-stock Kawasaki KX250F is damn good. But we're motocross dudes just like the rest of you, and somehow, we always find something out there worth improving or at least tinkering with. With this particular steed, a couple of areas warranted attention.
These aren't bolt-on-for-nothing-but-looks improvements. Even though I have needlessly applied different parts just because, I tried to keep the green bike additions practical and necessary.
First and foremost on the improvement list was to lower the sound level and improve the sound quality coming out of the stock bike. The standard muffler on the KX is like Axl Rose-it made sweet music for the first part of its life, but soon, it went insane, became blown-out, raspy and audibly horrific. I went to the race experts at Pro Circuit for some team secrets and was happily surprised when they told me about their '08-spec Ti-4 GP system. The new full-exhaust setup is built to meet the quieter 2008 AMA sound limits set at 98 decibels. The hot-rod pipe came boxed with a quiet insert and a spark arrestor factory installed, so I bolted it on just like that.
Along with their titanium tubules, the PC gang also sent a sweet little plastic bag of brass goodies to get the bike jetted to their high-power recommendations. In the past, PC jetting specs have been right on so this was a real no-brainer for me. The differences in orifices were pretty big over stock, or rather small, as almost everything was leaned down to complement the new exhaust. The race shop has jetting recommendations for any bike at any altitude, so feel free to pick their brains for a spec just right for your track.
The first few testing days were hit and miss with the pipe and jetting combo. The aggressive settings handed down from Mitch Payton's speed-freaked cronies were enough to put the bike into a more finicky state compared to the simple stock setup.
Right off bottom, the bike developed a "pit fl utter," a jetting "miss" that ran rampant in the pits while cruising to the track but disappeared completely when you started in at race pace. Fuel screw adjustments took it down a notch throughout our experiment, and some pilot jet sizes were swapped when we adjusted too rich or lean. I finally settled back at the original PC recommendations because the bike ran so well on the track that I stopped caring about the almost-phantom rich slow-circuit.
The stock '08 KX-F has a great motor, miles ahead of the abrupt, snappy '07 model. If anything, it's a bit soft on initial pickup but comes on strong and controllable through the mid and finishes with a stout top-end. With the PC setup, the bottom woke up big time! We now have torque downstairs with absolutely no compromise to the delivery throughout the rest of the rpm range. The best thing: Our favorite combo is with the quiet tip and sparky installed. And I mean a unanimous favorite from everyone on the bike and listening to it from the sidelines. The green beast now runs stronger than stock everywhere and is making "Sweet Child O' Mine" music. With this simple addition, the bike is running with the same fire-breathing character of other full-blown PC race motors I've tested. It loves to rev and will go to the moon. But it cranks better downtown. Nothing is better than great power and a clean sound. Rock and roll!
Since Ryan Orr was around helping Denison with his Suzuki, I let him kill some laps on the Kawi and he felt the new bottom-end pickup in power was impressive. He also thought the bike delivered a controlled helping of power increase all the way through to a killer overrev. These are his words. He says stuff like "killer" all the time.
To update the control department, I turned to ProTaper. The stock 7/8-inch bar on the KX-F isn't the epitome of high-quality control and I dig tapered bars, so a ProTaper Evo Reed/Henry bend went on top of a ProTaper forged top triple clamp. The clamp has the option of three different levels of vibe-killing bushings under the bar mounts (as well as rigid aluminum). I left the medium-strength yellow bushings in. I stuck on some new Pillow Top ProTaper grips as well. The compartment was opened up a bit, but the sweep on the Reed/ Henry bend isn't exactly where I want it. I was close to cutting the bar down a bit, until a few rides in, I began adapting to the bend. I'll try different bends soon. Stay tuned. Sometimes I can't stop tweaking. The new Pillow Top grips are sort of funky. They have a bigger-diameter feel to them since they're so cushiony but don't pump up your arms like bigger grips can. I plan on keeping them on until they tear off...especially since the instant grip glue seriously sticks!
Since the shootout took its toll on a few cosmetic and high-wear parts, I called up the gang at ridePG.com and had their graphic geniuses develop a cool theme of custom Gripz goodies. The Gripz material is my favorite, and the custom look is always nice compared to the same old stuff. I even plugged my sponsors with graciously applied logos for supplying parts for the bike. Next time, I'll request the entire bike be printed in the Gripz material. The stock plastic in "cool" black looks old and beat quicker than Angus from AC/DC after a night of partying. Thus, I recommend covering up the black plastic with graphics.
The only other parts in dire need of replacement were the chain and front and rear tire. I immediately went back to stock with the Bridgestone M403/404 front/rear combo. These meats are easy to love. RK racing chains got the call and provided its ultralight MXZ3 racing chain, and then I was done. What I got out of this project was simple: I managed to take the best 250F bike of 2008 and make it faster, quieter and better looking. Encore!
Parts List
Pro Circuit Ti-4 GP full system with quiet tip and spark arrestor
PC Jetting
RK Excel Works MXZ3 racing chain
RidePG.com custom graphics and preprinted backgrounds
ProTaper forged top triple triple clamp assembly
Reed/Henry-bend Evo handlebar
Pillow Top grips
Instant grip glue
Tires
Bridgestone M403/404 tire combo