Story by Trevor Hunter, Photos by Trevor Hunter, Mark Kariya, & Ryan Vitelli
In the last few years, 250F’s have taken over the 250 classes across the board. While thumpers have been the norm in motocross, four-strokes have slowly been phasing out the classic two-stroke in off-road racing. Nowadays, all of the fast guys race 250F’s and it’s been a hot minute since a 250 two-stroke has seen the podium at a national level grand prix race. Of course, racers can’t leave their bikes alone and a majority have some form of performance mods to try and squeeze every last ounce of performance out of their bikes.
We’ve been thoroughly impressed with our YZ250FX long haul test machine and when the time came for a rebuild after 80 hours, the folks down at Yamaha gave us a complete GYTR High Performance Head setup to install. That kickstarted this build into what it has become today.
The main piece of the puzzle is the GYTR head. Being more of a two-stroke guy, the words high performance and four-stroke being used in the same sentence kind of scare me. Sure, the power and performance will be better. But at what cost? Will it be more of a headache than it’s worth? It turns out my worries were for nothing.
As you can read in our Product Test on the GYTR unit, the head is a winner. The performance gains were everything we hoped for and really helped the areas we felt were lacking for our intended purposes. Best of all, it can be run on pump gas and installation is pretty simple for a four-stroke. The increase in torque and power across the spread, especially up top, really took this bike up a notch and made it more fun to ride while also being even more competitive.
Since the motor had 80 hours on it and we were going to boost performance inside, we went with a full rebuild. We initially installed the GYTR head and only replaced the top end, but some really hard racing hours and running low on oil at one point combined with boosting performance took its toll and expedited the life of the bottom end.
We ended up losing a rod, though we were careful to stop riding before it did any real damage. However, this called for a full rebuild and we turned to ProX Racing Parts. We replaced the full top end, rod, and gaskets with ProX parts and the main bearings with Wiseco pieces. The cylinder could have been reused, but we ended up replacing it with a new OEM piece since everything was already apart.
We’ve used ProX parts in the past and have always had really good luck with their pieces. They are typically very close to, if not as good, as OEM specs and the quality is as good as any when it comes to aftermarket parts. As we get more hours on this engine, we’ll provide an update on the longevity and durability of the ProX components.
Precision Concepts Racing originally valved our suspension and we’ve been working with them on finding a good all-around setting for this off-road build. With both desert racing and GP racing in the plans, it makes finding a great suspension setup difficult but the Precision Concepts stuff translates well to the diverse terrain we race in. From the desert to most GP tracks, we can feel comfortable on the FX only performing minor clicker changes from track to track or to the desert.
With the motor and suspension taken care of, it was time to clean the bike up. It was pretty beat looking after 80+ hard hours and it needed some love. Cycra hooked us up with a full Powerflow Body Kit to refresh the broken and scratched up plastic. The fit and finish is as good as any and everything lined up perfectly as we expected. The Powerflow Kit is slightly different from the replica plastics and it thins up the bike slightly and offers a racey look to it, something we noticed and liked. Additionally, the Cycra Skid Plate offers a lot of coverage and it’s taken on some rocky desert racing with ease.
DeCal Works Graphics gave the bike some shine with a glittery look in the graphics and a cool design. The install and finish of the DeCal Works graphics are up to par and better than a lot of other graphics we’ve installed. Everything lines up, they don’t bubble, and it’s easy to work with.
Looking for some longevity out of this bike, we’re running a DDC Steel Rear Sprocket paired with a Fire Power O-Ring Chain. The DDC sprockets last seemingly forever and with the little wear that it receives, the Fire Power chain should last quite some time as well. We also replaced the stock battery with a Fire Power unit as the stock Yamaha batteries are on the weaker side and don’t hold up to the abuse as good as the Fire Power units do.
TM Designworks’ Slide-N-Guide Kits are another part that could outlast the bike itself and perform well in the off-road conditions. Bullet Proof Designs Radiator Guards, Rear Disc Guard, and a Swignarm Guard will help protect the bike in the elements. The flimsy plastic disc guard that comes stock on the Yamaha isn’t ideal for desert racing, but the Bullet Proof unit is as tough as nails. Likewise, the Swingarm Guard will help keep the chain guide tabs in check when bashing through rocks and logs.
Dubya USA relaced our stock hubs to new DID hoops. Our stock rims were getting to be more square than round and needed an uplift. We went with silver as they look better for longer and wheels take a good beating racing off-road. We mounted Dunlop MX53’s front and rear stuffed with Nitromousse’s to keep us hooked up and flat free.
Of course, no off-road race bike is complete without a large tank and dry-break. IMS has us covered with a 2.8 Gal tank so we can go the distance and refuel in a hurry. Our stock front rotor was pretty worn and affecting the braking power, so we replaced it with a standard floating front rotor from Braking. Finally, we got tired of breaking and bending levers so ASV F4 Levers have helped our lack of talent and balance and resist breaking and bending when we fall.
Overall, there aren’t a ton of modifications to this bike, but everything on it has a purpose. Whether it’s to get more performance out of it or to add durability, or to simply replace worn stock components, everything on this GYTR built YZ250FX was thought of.