WE RIDE A HOT-ROD YAMAHA YZ250 TWO-STROKE
The Yamaha YZ250 two-stroke is a timeless testament to, “if it ain’t broken, don’t fix it.” With roots extending back to the inception of Yamaha’s YZ range in 1974, this bike has turned heads for over 50 years. The YZ250 (and YZ125) introduced the world to innovative designs like the reed valve, single-shock suspension and power valves. Now, the YZ250 turns heads with its heart-warming two-stroke melody, sharp and modern bodywork, and its beautiful expansion chamber.
Over the years, MXA has criticized Yamaha for neglecting their first love. After all, this engine hasn’t received any real changes since 1999; the frame has been the same since 2005; and the Kayaba SSS forks have remained basically the same, despite spring rate and valve setting updates, since 2006. However, our tune has slowly changed from critics of the lack of updates to thankful for what we have.
Yamaha’s YZ250 is the last carbureted two-stroke from the “Big Seven” OEMs. Honda, Kawasaki and Suzuki gave up on two-strokes 15 years ago, while KTM, Husqvarna and GasGas just recently moved to high-tech electronic fuel-injected two-strokes. For years, we have admired KTM’s investment in the two-stroke market and wished that Yamaha would invest some of the money they saved by not making changes into something more than BNG. However, KTM’s teething phase with their all-new EFI two-stroke engines has made the old-school Yamaha YZ250 look better in many ways. New technology always improves with time, and the new fuel-injected Austrian two-stroke engines certainly have lots of room for improvement. The carbureted YZ250 comes in handy as the only tried-and-true smoker on the market today—one that every experienced tuner knows like the back of their hand.
BESIDES ITS IMPRESSIVE HISTORY, STEADFAST ENGINE AND PLUG-AND-PLAY ALUMINUM FRAME, THE YZ250 IS FUN TO RIDE, AFFORDABLE TO OWN, AND EASY TO REBUILD.
Besides its impressive history, steadfast engine and plug-and-play aluminum frame, the YZ250 is popular for being fun to ride, relatively affordable to own, and easy to rebuild. It didn’t take much convincing to convince the MXA test riders to test this freshly built 2023 Yamaha YZ250 two-stroke.
Tom Morgan handled the engine modifications, and ParaPros helped rebuild it. Tom ported the cylinder and milled the head. After changing both the head shape and combustion chamber volume, the YZ250 then required high-octane VP race gas. We used C12 fuel mixed with Klotz R50 oil at a 40:1 ratio. Tom also bored out the carburetor to boost over-rev, and added a Moto Tassinari V4Force3 reed valve and an FMF pipe and Shorty silencer to top it off.
While it was apart, Tom rebuilt and rebalanced the crankshaft to lessen vibration. The KTM two-stroke engines come with stock counter-balancers, and while the YZ250 is no 500cc rattle box, balancing the crank would add some smoothness to the engine’s harmonics and decrease some of the vibration coming through the bars. For the average YZ250 owner, it’s probably not worth splitting the cases to balance out the crank to get these minor benefits. But, when you are building an MXA project bike, you go whole hog. For us, it didn’t move the needle on the track, because it still felt like a normal YZ250, and we were good with that.
Once Tom Morgan’s work was done, Jay Clark stepped in to cover the rest of the bases. Jay added a Rekluse TorqDrive clutch. He used the stock Yamaha basket with the stock YZ250 pressure plate. He just used the Rekluse fibers, steels and springs. The Rekluse kit also comes with sleeves that go around the basket’s tangs to keep the plates from notching them. These are a really nice touch, and although they aren’t as effective as a high-end clutch basket, they are infinitely easier to install.
Wiseco supported the build with their standard-bore top-end kit that ParaPros installed, as well as CV4 radiator hoses and a CV4 high-pressure radiator cap to keep the coolant flowing inside the engine instead of inside the overflow hoses. ProX provided the alloy rear sprocket and gold chain, while Cometic Gaskets filled all the most important joints on the YZ250 engine.
For breathing and cooling, the YZ250 used Uni Filter’s two-stage air filter and the radiators that were reinforced with bracing by MXA’s favorite radiator company—ICW. Dunlop MX33 tires were the rubber that met the dirt, and they were mounted on stock YZ250 wheels.
Another favorite stop when building a project bike is Race Tech. They re-sprung and re-valved the suspension with the vet rider in mind. We ran ODI Podium Flight Bars with the Champ bend and ODI Emig V2 lock-on grips. Additionally, Lightspeed made the factory-looking carbon fiber ignition cover, and Scar Racing made the ultra-sharp titanium footpegs.
Each step got us closer to building a hot-rod Yamaha YZ250 that could suit any skill level, even though we were aiming at the typical vet rider.
Works Connection had a long list of goodies on our YZ250 two-stroke. We used their hour meter and mount, their front-brake rotating bar mount, Elite clutch perch assembly with the clutch lever, front brake reservoir cap, steering stem nut, chain blocks and bike stand. MX Plastics provided the fresh bodywork, Decal Works decked it out with a semi-custom graphics kit and preprinted number plate backgrounds, and MotoSeat provided the gripper seat cover.
In the pits, the Tom Morgan Racing-tuned YZ250 kicked over with strong compression and a crisp two-stroke idle that revitalizes every test rider’s soul. The raw titanium FMF pipe and the iconic shorty silencer reminded us of why we get out of bed in the morning. Of course, if you look good and feel good, you ride good, so we dressed our test rider in some Blue Angel-style Alpinestars gear to match the blue and yellow Decal Works graphics theme on the bike. Even the FMF goggles matched the gear for this test.
FOR BREATHING AND COOLING, THE YZ250 GOT A TWO-STAGE UNI FILTER AND RADIATORS THAT WERE REINFORCED BY MXA’S FAVORITE RADIATOR COMPANY—ICW.
On the track, the YZ250 was stronger and faster than the stock model by far, but it was also smooth and linear. Our test riders spend more time on four-strokes than two-strokes these days, so they especially appreciate it when an engine builder can tune a two-stroke to have a four-stroke-like low-end power character, but still snap, crackle and pop from the midrange on up.
We have always appreciated Yamaha’s YZ250 two-stroke for its smooth roll-on power, and we praise its Keihin PWK 38 carburetor for the rider-friendly crack-of-the-throttle character. Usually, when a tuner goes searching for more power, they have to sacrifice ponies somewhere on the rpm curve. Thankfully, Tom Morgan Racing (TMR) kept the smooth, initial throttle response that we know and love. Obviously, it’s still a smoker and still a 250, but the power was linear nonetheless.
The suspension was too soft for our faster test riders, but it was perfect for our vet and lower-level novice test riders, which was its intended audience. Compared to the stock suspension, the Race Tech setting was plusher at the beginning of the stroke, with a healthy amount of bottoming resistance when we went faster, jumped further and braked harder.
MXA APPRECIATES AN ENGINE BUILDER WHO CAN TUNE A TWO-STROKE TO HAVE A FOUR-STROKE-LIKE LOW-END POWER, BUT STILL SNAP, CRACKLE AND POP ON TOP.
Obviously, Race Tech has been around for a long time with experience on all different models, but it especially makes it easier for them to hit the nail on the head with a vet rider setting when the frame hasn’t changed since 2005 and the suspension hasn’t had a big update since 2006. The bodywork was new in 2022, and the YZ250 also gained a new seat. The 2022 updates made the front of the bike 36mm narrower at the pointy end of the shrouds and 7mm narrower in the middle where your knees grip. Even the seat was 5mm taller in the middle and 6mm lower at the front, creating a flat profile that helped the rider sit “on the bike” rather than “down in the bike.” Of course, this brings the seated ride position up a few millimeters, but this only helped the YZ250’s exceptional handling. Now, it has a more modern and ergonomically proper rider triangle. If you want to refresh your 2021-or-earlier-model YZ250 to the 2022 spec, you’ll need the subframe, fuel tank, seat, shrouds, side panels and rear fender.
Overall, the YZ250 was both fun and boring for the MXA gang. It was fun because of its smooth power and plush suspension, but it was boring because there was nothing exotic or unexpected to work through during our test. This was a straight-forward YZ250 project, which you can use as inspiration to build your next bike.
YZ250 SUPPLIER LIST
COMETIC GASKET: www.cometic.com
DECAL WORKS: www.decalmx.com
FMF RACING: www.fmfracing.com
ICW RADIATORS: www.icwbikestands.com
KLOTZ LUBRICANTS: www.klotzlube.com
LIGHTSPEED CARBON: www.lightspeedcarbon.com
MOTO SEAT: www.motoseat.com
MOTO TASSINARI: www.mototassinari.com
MX PLASTICS: www.mxplastics.com
RACE TECH: www.racetech.com
SCAR RACING: www.scar-racingusa.com
UNI FILTER : www.unifilter.com
VP FUEL: www.vpracingfuels.com
WORKS CONNECTION: www.worksconnection.com