2008 250F MX Bikes Fine-Tuning - Dirt Rider Magazine

Why modify? Why tweak? Why tune, tinker and tool? Because we're dirt riders and we can. But more so than just being able to, we customize our rides in an effort to reach a place more gleeful than the standard manufacturer baseline and right in tune with our personal tastes. For 2008, the 250F class was a sweet bunch of bikes to rate. All are solid and capable in stock trim. But being regular riders like you means we have regular rider complaints. So instead of just sitting around whining about a loud pipe or unsupple suspension, we went to work. This is how we turned a class of stockers into our perfect track weapons.Ready... set... mod!Make Mine Evil
Modified 2008 Honda CRF250R

The new CRF250R looks plain but runs evil. Yeah, complaining got me to this point, but making this bike mine was just a matter of transformation.When I saw the One Industries Massacre kit, which looks like a white version of the limited-edition black CRF, I knew what I wanted my bike to look like, regardless of what my staff thinks. Even the freestyler! Now it was just matter of getting it to run more of my style. Look evil and run plain!Since Karel called big bore before I could do anything, I was left with a tuning issue: Taking the insane power of the CRF and making it more usable, something big bores often accomplish. Let's face it, if every track was running up a 30-degree incline the whole time, the CRF is just fine. It loves a huge load on the motor. But for me it spins up too fast and burns through its power way too quickly on level ground or in low traction. The suspension is probably the best in the class for me and I'm learning to like the aggressive handling of the bike, just keep the steering damper cranked to near full stiff!The simplest thing to do, in my opinion (as well as the Dunlop guy), was to put a larger 110/80-19 rear tire on the bike. More traction, more drag on the motor, right? Well, this was correct as the D756 Race Replica tire I threw on the back did just that. But what it did wrong was get too much traction too soon, making the bike prone to bogging in the turns if the revs weren't up where they needed to be. It was a nice easy try, yet unsuccessful-sort of.Another easy fix might have been the pipe. My experience with Dr. D exhausts has been great as they seem to favor a ridable powerband over what numbers they can squeeze out of a dyno. I feel the stock CRF sounds a bit raspy as well, so I slipped on a full Ti Dr. D pipe and header ($779.95), single muffler of course. The folks at Dr. D were quick to point out the two-pound weight savings; I replied asking if they had a spark arrestor and a quiet insert as well. What the pipe did was simple: It boosted the already great low-end of the CRF into an even better low-end pull. The throttle response got better everywhere and the bike was quieter at real-world riding rpm. It fixed the wrong end of the power spread, but it also pulled the bigger tire better! The top-end was still fast and ferocious. The spark arrestor changed nothing, and adding the quiet insert killed off any of the bottom-end gains but would allow me to be off-road-legal if I had the need.My next step was flywheels. Steahly Off-Road makes complete bolt-on flywheels ($149.95), and I ordered up both a 9- and an 11-ouncer to see what they would do. First was the lighter of the two. With the special flywheel puller it was a 15-minute job to switch it out, and the resulting change in the power was instant. It slowed down the rate of rpm increase through the power spread. This was what I was looking for. The added weight surprisingly didn't hurt throttle response one bit and actually seemed as if it aided the bike in finding traction exiting turns. So if 9 ounces was great, 11 ounces must be better. I had the cover back off in a couple of minutes and dropped in the heavier flywheel-I'd gone too far. Now there was just a bit of lag if the rpm dropped too low and the upper end felt mostly the same, except the bike did pull a little better at the very top of the power spread, yet the 11 just wasn't worth the trade-off.In the end, my Massacre CRF was a hit. The tire, pipe and 9 extra ounces of weight combined to tune the bike's delivery into a way more usable power spread for me. Jesse Ziegler agreed with me on all accounts that I'd made the motor way more usable. Ad sales guy Damian Ercole almost pulled a couple of holeshots at the White Brothers Vet World Championships in a field of 450s, claiming that he was pulling them on the monster uphills, too, because of the great traction and being able to use all the power the bike had, never worrying one bit about the handling. He was even able to pass 450s on a 250, which, he said, made him "feel big." Sure, the white CRF was a love it or hate it in the looks department, but now the engine character wasn't that way for me or anyone else who rode this project.Parts List
Dubach Racing Development titanium full exhaust system
Steahly Off-Road 9 oz. flywheel
One Industries White Massacre kit
Jimmy Lewis attitudeTires
Dunlop D756 Race Replica rear

Rock! Rock! Rock!
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 flutter," 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 glueTires
Bridgestone M403/404 tire comboRotten Eggs And Fire-Works
Modified Suzuki RM-Z250

You know the face people make when something smells really, really bad? Whether it's rotten eggs or dirty moto socks, we, as humans, are automatically programmed to wrinkle our noses and half-open our mouths in disgust at the slightest trace of stink. Well, that's the face most of our test riders were making when discussing the performance of the 2008 RM-Z250's fork after our last day of shootout testing. Yes, the RM-Z is a great bike and, no, the suspension isn't bad fresh off the showroom floor, but after several days of hard testing on some seriously rough tracks, the Suzuki's front end had seen more break-in than a hotel room full of O.J. Simpson memorabilia. The bottoming resistance went out the window, and the bike's original vote of confidence was beginning to dwindle right along with the ride height. Something had to be done.Barely cooled down from one last day of evaluations with our schoolboy testers (see the featherweight impressions in the March issue of Mini Rider), the Suzuki was dropped off at RG3 Suspension for a pick-me-up. Along with fresh oil in both ends, the suspension was revalved to accommodate heavier pilots, with the end goal being to maintain the original settling in turns while doing something about the awful clank-clank that resulted from landing a bit off target. To complement the new setup, an RG3 rear link was also installed to reduce the dead blow to the shock on hard hits.After tooling with the suspension, I found it prudent to try to fix some of our other complaints about the yellow thumper. Since I feel that the stock Renthal Fatbar has a cramped bend that doesn't complement the rest of the Suzuki's ergos very well, it was off with the old and on with the new 997 Twinwall bar and half-waffle grips. The tires were fairly well burned after all the testing, which meant that some new meat was in order-I went with the Maxxis Maxxcross IT on both ends. Next, I turned my attention to the motor, mostly out of curiosity rather than complaining since engine performance is actually one of the RM-Z's high points. Personally, I like my four-strokes to run a tad stronger on the mid and top-end, so I got my mitts on a pair of Leo Vince exhaust systems to see what they could do as far as boosting the power. I then bumped the gear ratio from 4.00 to 3.92 with a fresh 47-tooth Renthal rear sprocket and installed a Twin Air Dual Stage filter, which is designed to increase airflow and enhance the overall response. To finish things off, I slapped on some fresh Throttle Jockey graphics and a gripper seat cover, just so the 'Zook didn't feel left out next to Jimmy's howling death-monkey stickers.It took about half of a lap aboard the RG3 suspension to realize how much better the RM-Z was working. Two more days of riding confirmed that even with some break-in, the new setting had the machine riding higher up and using more of the stroke without all the bottoming hassles seen previously. Due in part to the RG3 rear link, the suspension took on a plush feel with quick-acting resistance in all the right places. The change was just what I was hoping for-not drastic enough to botch the original strengths, but super improved all the way around.

The slightly faster gearing, Maxxcross tires and new Renthal bar were all an instant hit, but I hit a virtual wall when it came to the exhaust. Jumping right to the titanium full Leo Vince system, golf partner/testing homie Ryan Orr and I were less than stoked on the changes to the power. A great supercross pipe, the full system gave the bike a quick-revving, narrow-windowed power that didn't work well on any of the three outdoor tracks that we rode. Feeling the poopy-face coming on again, we were happy to find success with the stock header/ Leo Vince stainless steel slip-on combo, although the broadened power and better mid was accompanied by boggy response and sporadic hesitation. The golden ticket ended up being in the spark arrestor tip, which calmed down the throttle response issue while only slightly suppressing the newfound power, ultimately adding more meat on both ends and boosting the midrange considerably over stock. We rotated through all of the combos-including stock-once more to make sure we were happy, and then settled upon the slip-on can with S/A screen as the final choice.In my opinion, the revised RM-Z250 makes for one heck of a race package. By stepping up the suspension performance, opening up the cockpit, slightly tweaking the gearing and broadening the power throughout, we transformed the entire feel of the bike. What's more, I didn't once have to remove the motor from the frame or crack the carb to fiddle with the jets. All of these mods were completed without breaking the bank, and thanks to the spark arrestor, the bike is now much quieter and-best of all-off-road-able. You know that face that people make on the 4th of July whenever a huge bundle of colorful fi reworks explode in the shape of a massive, awesome peace sign? Well, I'm making that face now.Parts List
Leo Vince X-3 stainless slip-on exhaust
Throttle Jockey graphics and gripper seat cover
Renthal 997 Twinwall handlebar, dual-compound half-waffle MX grips, 47-tooth rear chainwheel
RG3 linkage tie arm and cam with bearings, front and rear suspension revalve
Twin Air Dual Stage filterTires
Maxxis Maxxcross IT front and rear tiresHey Big Boy
Modified Yamaha YZ290F

This is how it works at Dirt Rider meetings: Jimmy acts as the moderator,sort of keeping the welter of ideas and comments somewhat on track toward the eventual completion of a magazine. And while he easily could, he doesn't simply grab up all the cool/fun ideas and stories for himself. He does pull rank on some, but many others are sort of thrown out there like a dolphin trainer hucking smelt to see how many tricks we'll do to get it.During the discussion of modified 250Fs, Jimmy mentioned in passing, "We should probably do one as a big bore." I'm trained like Pavlov's dogs-say big-bore 250F and I start to drool. But I didn't let the involuntary salivation slow me. With speed that would dazzle a game-show host, I slapped the table and claimed the big-bore bike. We were supposed to be picking a machine that had specific problems that bothered us, but all of the 250Fs are fun, and I love to ride any of them. But for a person my size, they can all stand more displacement.Since I was looking for a big-bore candidate, the Kawasaki, Suzuki and Yamaha were the most appealing. Each will take a larger bore without any other modifications, so I was hoping for one of those. Jesse jumped in and claimed the Kawasaki and Denison was already started on the Suzuki, so that left the Yamaha. But I didn't see that as a third choice. I get along well with the Yamaha, and the engine has been around for many years, so there are plenty of bigbore kit options available. We were looking for a reasonably priced option that was somewhat in line with the price total for the other bikes. And personally, though I've never had a problem with an iron sleeve, I wanted a kit with a nikasil bore and aluminum sleeve like a stock bike has.A little checking revealed that Athena had a well-priced kit that included its own brand cylinder that increased displacement to a whopping 290cc! The kit comes complete with everything you need for around the same price as a complete exhaust system ($756.77).Installing the kit was easy. It comes with the Athena cast cylinder, piston, rings, gaskets and circlips. The job was as simple as changing a stock piston. Athena includes directions, and since I had never rebuilt a Yamaha on my own, I was happy to have the included manual. The only "special" tool I used was a torque wrench. The cylinder surface looked very shiny and I was tempted to run a hone through it, but Athena reps said no. I rebuilt the top end of the engine, installed graphics, prepped the bike and wrestled on new tires during a single day in the garage. Except for small letters on the cylinder and a notably deeper growl, there's no evidence that the bike is anything other than a stocker. The stock plastic was looking tattered and scratched and it had white marks in the blue. I contacted Acerbis and replaced the front fender with a blue one, then added a white one on the rear. Most of the white marks were on the rear fender, so it seemed easier to switch than fight, and I like the way it looks.When it came time to break it in, I headed to the I-5MX track with a couple of friends. They followed me to the track with 450s and I thought, "This shouldn't be fun for them. During break-in I won't be able to go fast or do the jumps." Surprise! With 290cc on tap, the YZ handled every jump on the track that I normally do and all without ever opening the throttle past half-open. I gave the engine three good rides that got it good and warm without lugging it hard or spinning it unmercifully, then let it cool in between.

Then it was time to see what she would do. The engine doesn't really feel faster at high rpm, but it's strong and responsive at every other rpm. The best way to enjoy the engine is to purposely not downshift for turns. The 290 pulls through strongly then catches fire on the way out of the corner. That sort of power is awesome for a heavier rider like myself. I wasn't sure a faster rider would feel the same, so I had Jonty Edmunds try it. Jonty is more of a 450-size guy, but he has youth, fitness and the talent that I don't.After a couple of motos, Edmunds had this to say, "I thought the 290 was great. I prefer 250Fs to 450s because less power is more fun. Having said that, 450s have an advantage because you can be lazy, but if you try to ride them hard, they can kick you in the ass. 250Fs are more fun but you have to try harder. The 290 was the best of both worlds. It allows you to be a little less on the ball as far as being in the right gear all the time because of the additional cc giving it a midsize four-stroke feel. You can also ride it hard and it won't get away from you. Sometimes, what takes away a bit of the fun factor of the 250Fs is when you're riding them hard, in high revs, the handling is compromised a bit and they get twitchy. In the midrange, the bikes just handle better, and with the 290, you can do just that: Keep it in the midrange. It started easily and the carburetion was perfect. In many ways, it's the kind of bike I wish manufacturers would produce. I think it'd make a great woods bike with the kind of power it has. Progressive, smooth, strong but not too strong."Jonty and I are in age-group classes, so a 290 is legal. I was curious what a younger, lighter rider would say, so I dangled the bike like a carrot in front of Chris Denison. And, again, it was a hit. "Once I got the suspension dialed in, I was super pumped on how the 290 worked. The added power gave the motor the lugability of a bigger bike without feeling overly powerful (or lethargic), and the capacity to ride a gear higher everywhere was outstanding. Considering how little this mod costs, I'm pretty surprised that big-bore kits aren't more popular."All things considered, I'm delighted with the 290. It isn't perfect, since the engine-braking increased and on full-traction uphills like we find at Piru MX, the engine feels a little reluctant to rev. On the other hand, for every other track I felt no negatives at all other than learning to delay downshifts to lessen the effect of the engine-braking. The jetting isn't odd, starting remains easy, it doesn't run hot or feel finicky. Athena calls for a new piston at 15 hours, but I plan to replace it at 20 hours. That's when I'll finally be able to give the 290 a total thumbs-up. In the meantime, I'll just enjoy the heck out of running up the hourmeter. It's a tough job, but I did volunteer.Parts List
Athena YZ250F complete big-bore cylinder kit
Acerbis front and rear fender plastic
Factory Effex Evo 5 graphics kitTires
Dunlop D745/D756The Under-Dog
Modified 2008 KTM 250 SX-F

You're like me, I know it. You skim over the early paragraphs in every shootout about how the new bikes are all so good, all so close, how ranking them was splitting hairs, and you agree-for a moment. Then you read on about the bikes' rankings and you can't help thinking of the last place bike as a dog. I'm newest on staff, last to pick, and I got the pound puppy-the little orange KTM. Its weakness, to me, was obvious-the suspension was a step behind the others. But the bike corners better than the best of them and has a strong and very reliable engine. Suspension is the easiest thing to fix, so I set out to turn my mutt into a superhero.My first trip was to Factory Connection for a full revalve and spring swap of both ends. Factory Connection also has some cool WP tricks, so it replaced the floating piston reservoir with a bladder-type reservoir, swapped out the rebound adjuster housing with its better-sealed unit, and made the move to a progressive spring in the rear. On the first trip out to the track the bike was clearly unbalanced-to me. Jimmy and Karel both rode the bike that day and didn't have major balance issues, but Jimmy's pace is higher and Karel has some pounds on me. Everyone agreed the bike had found a plushness, but I was stinkbugging around the track and needed a fi x. Factory Connection swapped out to a softer rear spring and that brought all the pieces together. Whereas the stock bike would pound my hands and make them sore, the new bike felt much more plush and in line with the rest of the 250Fs. The stock bike has big trouble on the little stuff, and this FC bike smoothed out that braking chop. The work isn't cheap, but most riders would benefi t from a revalve, and maybe springs, on any of the bikes, so think hard if this counts as a bike fix or a tuning modification you would do to any of the brands.

I wanted to see if I could do better still, so I did a full suspension swap to hlins components. Now this counts as extravagance, but I wanted to know what was possible. First I rode with just the hlins shock, and the bike instantly gained a more confident stance. The braking chop never wagged the bar, and the whole ride had a more stable and also more responsive feel. Then I added the hlins 48mm fork and the spring balance got out of whack again. Now the freer-moving front was tucking in the corners and in bad chop. It was clear the movement of the suspension was incredibly stiction-free, but the two ends weren't cooperating. A switch to a softer rear spring and everything clicked into place. The ride was everything you'd want. Way less jarring than stock, a controlled and connected feel in the rough, and a responsive bike in the corners. The great benefit of hlins seems to be the controlled way they transition from compression stroke to rebound stroke. Jimmy jumped on the bike again and really enjoyed it, though it was undersprung for him. Even a hard bottoming for him, which would usually mean a harsh tink! and bounce, was met with a dull, controllable thud that didn't disrupt the bike. The KTM seemed to gain that rare understanding of knowing what you want it to do and doing it through thought as much as input. The stock bike comes close to this feel on a smooth track, but bumps upset that ride. This hlins bike had it, smooth or rough, berm or fl at corner-the bike just felt right. It's not a cheap option, but for 2008, hlins is coming out with fork internals and seals to upgrade your stock front fork to this Swedish-massage ride. The rear shock and fork upgrade will still cost around $3000 and there's no way to get over that steep price tag without a good justification, so here's one-with four-stroke engine mods reaching new heights, suspension work, even this radical of a upgrade, is still the best deal for riding better and shaving seconds off laps. For the serious racer, hlins could be the answer.The modified bike rode on a set of Michelin tires- hardpack Starcross HP4s, oversize at both ends with a 90/100-21 on front and a 110/90-19 on the rear. The tires worked great on dry, flat corners, but anything soft or especially when wet, the terrain-specific rubber showed its limitations. In straight ruts, the tires could find so much traction they'd want to climb out, so these things were definitely grabbing dirt hard. For baked stuff, these tires find a lot of traction, but I should've been running a different tire for the loam.The bike also got a new seat from Enduro Engineering with more resilient foam. It helped cushion the acceleration chop a bit. This was a minor fix for me, but would be a critical one for heavier riders who push through the stock foam or for those who ride with a sit-down style.Finally, I had to make my bike look sweet, so I swapped the black and orange plastic for a set of full orange Cycra plastic (hoping that would get my Gavin Gracyk mojo on) then added KTM Hard Equipment factory graphics-in hopes of channeling a little factory rider speed. The bike sure looked better than the others-not really saying much in Jimmy's case-sheesh!Don't think of the KTM as the dog of the bunch, because no stock bike is going to be perfect for you. The KTM just needs a little more help in an area you're likely already going to throw some time or money into with any race bike, and dialing a bike's suspension is easier and more fun than trying to overcome some design fl aw. The KTM is a good little puppy, it just needs some training and some attention. And when you humiliate all your buddies on 2008's "losing" bike, just grin and tell them,"Life's ruff."Parts List
Factory Connection revalve, springs, bladder modification and rebound housing adjuster
Ohlins 48mm fork and TTX shock
Enduro Engineering stock height, hard foam seat
Cycra plastic with Powerfl ow shrouds
KTM Hard Equipment Factory Racing graphics kitTires
Michelin Starcross HP4