MXA TWO-STROKE FILES: WE BUILT A FULL-RACE YAMAHA YZ250

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By Dennis Stapleton

In all my travels throughout the world, as well as being an MXA test rider, I ride a lot of different bikes. It’s not uncommon for me to ride a Suzuki RM-Z250 in SoCal, jet-set to Kuwait and be racing a KTM 450SXF a few days later. This tireless schedule has made me less and less picky about things like handlebars, suspension valving, exhaust pipes or tires. My nickname should be “Chameleon,” because I’m good at blending in.

Having said that, I would rather ride a bike equipped with my favorite things if given the choice. It just so happened that I was on hiatus between trips overseas when Jody asked me to pick my favorite two-stroke and build it to my specifications. Naturally, I selected the 2015 Yamaha YZ250. It is so good right off the assembly line that making it my own would be a cinch. Unfortunately, the YZ250 is also Jody’s preferred race machine. Maybe I caught my boss on a good day, or maybe he took pity on me, because Jody agreed to part ways with his trusty blue screamer and let me have at it. I did MXA proud in my YZ250 dream-bike build. More important I addressed issues that have been evident with the bike for many years.

Here is what I did.

(1) Engine. I decided to leave well-enough alone. The YZ250 powerband is very broad and usable. I’m not a big fan of bikes that operate like a light switch—on or off—but instead want a metered powerband. Why? In my younger days I loved to crack the throttle and summon the beast within the bike. Those days are gone. At 34 years old, my right wrist and aging brain don’t allow me to ride with the fervor or gusto that I did as a pimple-faced teenager. I choose to roll the throttle on and think of the power as a direct connection with the rear tire. Lighting up the rear end like a top fuel dragster is counterproductive to my cause, which is moving forward to the next section of track. That’s why I left the YZ250 engine alone, aside from bolting on a Boyesen RAD valve, slipping a Boyesen Power X-Wing into the carburetor, and adding a DR.D pipe and NS-4 silencer. I have ridden big-bore YZ250s before, but I never liked the takeaways of going bigger. Punching out the cylinder changed the performance characteristics. In place of a broad powerband, the big bores were midrange only. That’s not my cup of tea.


The YZ250 has many charms, but can easily be personalized. The DR.D pipe, along with an extra tooth on the rear sprocket, allowed us to ride the bike a gear higher.

(2) Suspension. Johnny Cash once sang, “I’ve been everywhere, man.” I can relate. In all my travels I’ve had the pleasure of riding every type of motorcycle. Somehow I feel like suspension companies are coming up with as many space-age fork and shock designs as they are bikes. From AOSS to SFF, TAC, SSS, 4CS and more, I can’t keep up with all of the acronyms. However, there’s one type of suspension that will stand out until I’m 6 feet under, and that’s the Kayaba SSS. Why? There’s nothing better. I jump for joy every time I ride a bike with SSS suspension, because I know that it won’t throw me to the ground and put me 6 feet under. Fortunately, the Yamaha YZ250 is graced with SSS suspension, though it’s not quite set up for a 185-pound Pro. That’s why I sent the forks and shock to my pals at Factory Connection. They re-valved the suspension and installed a slightly heavier shock spring to keep the rear end from riding like a chopper through the bumps. A 1.5mm-longer Ride Engineering link arm stiffened up the initial part of the shock stroke and kept the shock shaft from drilling into my tailbone when bounding down whooped-out straightaways.


The engine remained stock, but the Boyesen RAD valve and Power X-Wing woke up a sleeping giant.

(3) Triple clamps. Ryan Villopoto and I don’t share very many similarities, other than the fact that we both race motorcycles for a living and like to steer with the rear end. Somewhere along the way in my professional career  It’s amazing what a few hundred dollars can do.I picked up the habit of sitting back on the seat and loading the shock in corners. There’s a school of thought that turning this way is wrong, but it works for me (and certainly for Villopoto). As a result, I’m not as concerned about triple-clamp offset as more precise riders. However, I understand the benefits of a sharper turning front end. I should note that the Suzuki RM-Z450 is one of my favorite bikes. Ride Engineering just released a 22mm-offset triple clamp for the YZ250. I had to try it out. The Showa steering stabilizer and one-piece bar mounts sweetened the deal. It set me back around $900 for the whole kit, but I believe in the benefits of the 22mm-offset clamp and steering damper—but not necessarily one without the other.

(4) Brakes. People say that MXA makes too big of a deal about front brakes. I think that we don’t harp on the manufacturers enough. In this day and age I cannot understand how a brand such as Yamaha doesn’t equip their high-quality, finely-tuned line of motocross bikes with the best front brakes that money can buy. After all, shouldn’t that be included in the sticker price? Instead, the YZ250 comes with a meager front-brake system that doesn’t perform well enough for my standards. I drop-kicked the 250mm stock rotor for a Braking 270mm W-Flo rotor. Although it doesn’t have the bells and whistles of the Batfly rotor, the W-Flo is more competitively priced. It’s amazing how the slight increase in rotor diameter vastly improves modulation and braking power. Now if only Yamaha and Suzuki realized the importance of an oversized rotor.


Factory Connection revalved the suspension on the YZ250. It held up higher in the stroke and kept the same progressive Kayaba SSS feel.

(5) Wheels. It’s nice to have a second set of wheels ready to roll in the event that I get in a pinch. I very well could use that excuse as to why I dumped money in a new set of wheels. However, that would be a lie. I gave Faster USA my service for two reasons. First, their wheels are manufactured in the USA. I believe in supporting the home team. Second, I was attracted to the gold rims, because they hark back to a foregone era when gold was de rigueur. Having my YZ250 stand out wasn’t the primary objective, but I didn’t want to make an ugly swan, either.

(6) Gas tank. Originally, I lined up an aluminum gas tank through a European buddy that I met during my travels, but something was lost in translation, and I ended up receiving a fruit cake instead. Why such an interest in an aluminum gas tank, aside from the obvious? Before the YZ250 was in my possession, Jody warned me that the bike had one major problem—the gas cap threads were destroyed in a crash. The stock gas tank was kaput. I could have easily ordered a new tank from Yamaha, but I took the road less traveled. I phoned up my friends at Bionix in Northern California and asked if they could fix the bum tank. They were up to the challenge and fabricated an aluminum insert and cap that took the place of the ruined threading. It is far and away the most trick part on the YZ250 and is reminiscent of what a Grand Prix team would run.

(7) Pipe. As previously stated, I chose a DR.D pipe and NS-4 silencer. Having previously tested the Bud Racing and Pro Circuit YZ250 exhausts, I can say with certainty that both have their charms. The Pro Circuit has a gun-and-run style of power with plenty of snap and over-rev. The Bud Racing pipe catered more to the midrange. I chose neither. Why? Doug Dubach, owner of DR.D, has been testing YZ250 two-strokes since dinosaurs roamed the hills of Glen Helen. He knows what the YZ250 needs, so I entrusted my faith in him. The DR.D system did exactly what I had hoped—increased the bottom-end and midrange gusto. In combination with an extra tooth on the rear sprocket, the pipe allowed me to carry third gear easier and lug the engine without fear of stalling in corners. Kudos to Dubach for giving me the inside line on how to maximize the YZ250 powerband. Next time I see Doug, I’ll be nice and not tease him about his age. Speaking of Dubach, I wonder if he drinks Ensure between motos.


Every so often we come across a part that captures the attention of the MXA gang. The Bionix-fabricated gas tank cap looked factory. Very cool.

(8) Aesthetics. Red Label designed my graphics package They had free rein to do what they wanted (except that Jody mandated the MXA helmet logo had to be on every bike). Using blue made logical sense, but Red Label threw caution to the wind and added green-and-white accents throughout. The design matched up nicely with my gold wheels and blue Mika grips. Mika handlebars, a Works Connection clutch perch, holeshot device, axle blocks, steering-stem nut, Boyesen clutch and ignition cover. A pleated Moto Seat cover and blue CV4 silicone radiator hoses also spruced up my project YZ250.

(9) Final words. I did what any motocrosser with a fairly large budget and a 2015 Yamaha YZ250 would do. I made logical choices based on past experiences and invested in components that actually made a difference. These are real-world fixes for the YZ250, and, fortunately, most of them don’t cost an arm and a leg. The only indulgences I made were in the Faster USA wheels and Bionix-fabricated gas tank. While the factory-like parts didn’t lower my lap times, they did make me feel faster—and that counts for something.

SUPPLIER CONTACTS
www.boyesen.com
www.braking.com
www.dubachracing.com
www.cvproducts.com
www.worksconnection.com
www.fasterusa.com
www.ride-engineering.com
www.factoryconnection.com
www.mikametals.com
www.redlabel.mx.
www.shop.motoseat.com
www.wiseco.com
www.lightspeedcarbon.com
www.dt1filters.com

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