Cheap speed: If you want to maximize the power of the YZ125, add
one tooth to the rear sprocket. You’ll love the extra drive.
Go bold: Aftermarket exhaust pipes can add two horsepower to the
YZ125 (and two-stroke pipes cost a lot less than four-stroke pipes). ( 4) Entry-level. A 125cc two-stroke is the perfect machine for a minicycle transplant. Q: WHAT DO WE REALLY THINK? A: We think that Yamaha has sat on the two-stroke fence for too long—although it is better than what Suzuki, Kawasaki and Honda did when they abandoned two-strokes six years ago. Yamaha hasn’t throw in the two-stroke towel yet, but their benign neglect is akin to death by a thousand cuts. Yes, we are glad that they still make two-strokes, but we aren’t glad that they still make 2006 two-strokes. Meanwhile, KTM sells 125cc, 150cc, 200cc, 250cc and 300cc two-strokes like they are going out of style. KTM can’t keep them on the showroom floors, while Yamaha doesn’t make enough two-strokes to even reach the showroom floors. If it’s worth doing, isn’t it worth doing right? The YZ125 could be awesome. ;
SETUP SPECS This is how we set up our Yamaha YZ125 for racing. We offer it as a guide to help you find your own sweet spot.
KAYABA SSS FORK SETTINGS We don’t believe that there is anything special about Kayaba’s metal parts. All suspension components are just stacks of metal shims and some oil. The real genius lies in Yamaha’s test program. They choose the correct spring rates, design real-world settings, and make the conglomeration of wafer-thin shims work like magic. The YZ125 has benefited from the advances Kayaba has made on the YZ250F forks, and, as a bonus, the Kayaba SSS suspension works even better on the 199-pound YZ125 than on the 218-pound YZ250F. Here is what the MXA wrecking crew ran for hardcore racing. Spring rate: 0.42 kg/mm Oil height: 340cc Compression: 11 clicks out Rebound: 6 clicks out Fork-leg height: 5mm up Notes: In 2007, the YZ125 came with lighter 0.41 kg/mm fork springs, which are better for many riders under the 150-pound mark. KAYABA SSS SHOCK SETTINGS For hardcore racing, we recommend this shock setup. Spring rate: 4. 7 kg/mm Race sag: 98mm Hi-compression: 1-1/2 turns out Lo-compression: 13 clicks out Rebound: 10 clicks out Notes: The high-speed compression adjuster is sensitive, so make small (1/8-turn) changes. It’s also a very important adjustment for keeping the rear wheel settled and for controlling wheelspin on hard, choppy terrain. MIKUNI TMX JETTING SPECS Yamaha has their jetting down, and our 2013 YZ125 ran clean. Here are the 38mm Mikuni TMX jetting specs: Mainjet: 430 Pilot jet: 40 Needle: 6BFY43-3 Clip: 3rd from top Air screw: 2-1/4 turns out Notes: Yamaha includes one richer (440) and one leaner mainjet (420) with the bike. The current 6BFY43-3 needle is a half-clip richer than the old 6BFY42-3 needle used before the global spec came into play.