We take a 2010 Yamaha YZ250 (which is virtually identical to the 2007-2009) fix its flaws to make it one great machine. Here are the eight things we did to make it more powerful, handle better and stop sooner.
(1) Front brake. Yamaha’s front brake is decent, but by no means great. We noticed that a lot of National riders use a Brembo front master cylinder in place of the Nissin to get more power. Rather than go that route, we switched the stock 240mm front rotor for a 280mm EBC oversize rotor kit. At 280mm, the EBC kit is 10mm bigger than most comparable oversize rotors. It stops phenomenally well (at some risk to damage in first turn crashes because of its size). The EBC kit (without pads) retails for $180. For information, go to www.ebcbrakes.com.
(2) Jetting. Back in 2007, Yamaha switched from the N1EJ needle to the newer N3EW needle. This needle solved most of the pinging issues, but if you switch to an aftermarket pipe, you should go up to a 180 main.
Shock spring. When Yamah#2;a went to the larger shock shaft back in 2006, it lessened the need to go stiffer on the 4.9 shock spring. The quick trick for riders who feel that the rear shock is a little too soft is to turn the high-speed compression in a quarter turn. Conversely, if you feel that the forks are too soft, try turning the rebound in about four clicks before going to stiffer fork springs. The slower rebound will have a crossover effect on the compression damping that could make the forks feel firm enough.
(3)Tires. We love the Dunlop 75#3;#21;6 rear tire, but question the choice of the Dunlop 742FA front. Given our druthers, we would swap to a 739 front for really hard dirt, a Bridgestone 403 for hard-to-intermediate dirt or a 756 (if you can find one) for any loam situation.
(4) Gearing. We added one tooth to the rear to tighten up the gear ratios, condense the power and produce a more pronounced surge. The stock gearing is 14/50. We run 14/51.
(5) Triple clamps: No matter what anyone tells you, do not change from the stock 25mm offset—it works best. MXA test riders have tried 22.5mm offset triple clamps, and they aren’t a very good choice. The 22.5s make the front end feel so strange that you think there is something wrong with the rear end. That’s not good.
(6) Pipe. Pro Circuit makes the best exhaust pipe for the YZ250, a#3;#11;nd they earned that reputation by making pipes for Chad Reed when he raced a YZ250 two-stroke. Pro Circuit (www.procircuit.com) makes two versions: the Platinum 2 for torque and the Works pipe for mid-and-up.
(7) Reeds. Choose between the Moto Tassinari VForce3 and the Boyesen RAD Valve based on your preference. The VForce3 produces a stronger midrange, while the RAD Valve offers more mid-and-up hit (especially if you remove the stock 5mm spacer plate). Boyesen’s number is (800) 441-1177, and Moto Tassinari can be reached at (603) 298-6646.
(8) Clutch. If you abuse the clutch, the cheapest fix is to install three YZ450F clutch springs in the clutch pack. The YZ450F springs are stiffer and will make the lever pressure greater, but really improve hookup and clutch plate life.