Changes shared between the YZ125X and YZ250X begin with suspension. Riders who know and love Yamaha’s KYB Speed Sensitive System (SSS) coil-spring fork and KYB shock will be happy to discover the components remain but are spec’d with revised damping at both ends to further improve bump absorption and cornering. Settings are model-specific and optimized for cross-country performance. A new scraper between the dust and oil seal in the fork has been added to improve reliability.
Brakes have been given attention with a more rigid front caliper, larger front pistons, and a redesigned 270mm front rotor with a 30 percent increase in contact area. The rear rotor has also been reworked with its outer diameter being reduced from 245mm to 240mm to decrease unsprung weight without sacrificing braking power or performance
The rear sprocket design is new and designed to be lightweight. Also, ergonomics have been revised with a flatter seat and narrower fuel tank design with smoothly integrated bodywork and slimmer radiator shrouds. A new front and rear fender design, and embedded graphics in the Team Yamaha Blue colorway help give the two-stroke models a modern appearance.
The most notably changed area of the YZ125X is its powerplant. Every functional part of the engine is new in an effort to increase power. This includes the crankcase, connecting rod, cylinder, cylinder head, piston, piston pin, and expansion chamber. Additionally, its Yamaha Power Valve System (YPVS) characteristics, exhaust timing, and compression ratio have been optimized to improve ease of use in the low- to mid-rpm range.
Along with a new intake design, Moto Tassinari’s VForce4R reed valve system and a straighter intake path are said to result in improved power high in the rpm range. Other new components are the Keihin PWK 38S carburetor and shorter, lighter muffler. The six-speed, close-ratio transmission has been revised with optimized gear ratios and wider gearbox teeth.
