If you’re a regular visitor to this site, you know that we are spoiled and always want more from our bikes. So when Yamaha builds a bike like the YZ250FX that has so many characteristics that we love straight off the showroom floor, we consider it a personal challenge to find ways to make it even better. After all, with several aftermarket companies making products for this model, how hard could it be? We set out in search of more power, better handling, improved stopping power and a little weight reduction on the YZ250FX. Here is what we discovered.

There is more than one way to increase the horsepower output of a machine. You can bolt-on aftermarket goodies such as an FMF 4.1 titanium exhaust system with a MegaBomb header, Stage 1 Hot Cam, and a Vortex ECU, or you can tune up some of the parts that come stock. You could have the crew at Twisted Development remove the backfire screen in the airbox, do some head porting and remap the Vortex ECU to match all the new engine work and bolt-on parts. We did all that, but it was still not enough to satisfy our craving for more power! So, we did what any logical person would do; we went up in displacement. After all, when it comes to power, there is no replacement for displacement, right? Cylinder Works makes a 3mm big-bore kit that comes with a cylinder, forged Vertex piston and a Cometic complete top-end gasket kit—pretty much everything you need except the mechanic to install it all. We topped off the performance part of the build with CV4 silicone radiator hoses, a high-pressure radiator cap, and a complete Hinson Racing billet-proof clutch system that includes fiber plates, steel plates, springs, a clutch basket, inner hub, pressure plate and a clutch cover.

With increasing horsepower out of the way, it’s all about the extras that complete the overall picture. We added the complete old-school Yamaha Yellow Powerflow plastics kit from Cycra to give the bike the retro look we wanted, and it also offers airflow features in the radiator shrouds, back part of the rear fender and the air-filter cover. The radiator shrouds are also slimmer in the rider cockpit area than OEM units. We installed Cycra’s new Ultra Pro-Bend-series handguards, a full-coverage plastic skid plate, Works Connection radiator braces and Elite clutch perch, and a TM Designs rear chainguide, because you can never have too much protection. Tusk has a brand-new lithium-ion battery that replaces the stock unit and is 2.5 pounds lighter. The YX250FX suspension is on the softer side right off the showroom floor, so Race Tech installed its Gold Valve system and did a little massaging of the shim stack for our off-road needs. We also took off the stock kickstand and replaced it with a CNC-machined Pro Moto billet unit.

Well, we learned a lot!  Sometimes a project turns out exactly the way we planned, but more often than not we are surprised by the end product. This build is a mixed bag. The engine power output is definitely increased way down low in the power curve, requiring short-shifting to make the bike work well. This bike worked really well in nasty tight sections where torque right off the bottom was needed to get over or out of something, and all the test riders liked that. But as far as top-end power, the new engine configuration does not rev as long or as strong as it did stock. With the Hinson clutch the action was still great, but the clutch pull was definitely on the stiff side compared to stock and took some getting used to. Another thing that jumped out at us right away was the increased air-intake noise. We actually put the removable backfire screen back in the Cycra airbox cover to quiet it down.
In the end, when it comes to weighing our successes and failures, this build was a learning experience. We expected to make a dragon, and what we got was sweetheart.


Twisted Development: www.tdracing.com
Cylinder Works:  www.cylinderworks.com
Hot Cams: www.hotcamsinc.com
FMF Racing: www.fmfracing.com
Uni Filter: www.unifilter.com
CV4: www.cv4.net
Renthal: www.renthal.com
Dunlop Tire: www.dunlopmotorcycle.com
Works Connection: www.worksconnection.com
Hinson Clutch Components: www.hinsonracing.com
Rocky Mountain ATV/MC: www.rockymountainatv.com
Tusk Off-Road: www.tuskoffroad.com
Cycra: www.cycraracing.com
Moto Seat: www.motoseat.com
Attack Graphics: www.attackgraphics.com
TM Designs: www.tmdesignworks.com
Race Tech: www.racetech.com
Applied Racing: www.appliedrace.com
Scar Racing: www.scar-racing.com
Pro Moto Billet: www.promotobillet.com
VP Fuel: www.vpracingfuels.com


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