| Attribute | Specification |
|---|---|
| Model Code | CG23C / B9U2 |
| Production Years | 2022–Present |
| Engine Type | 249cc liquid-cooled 2-stroke; reed-valve inducted |
| Transmission Oil | 0.75 L (Yamalube 4 / 10W-40 JASO MA) |
| Spark Plug | NGK BR8EG |
| Tire Size (Front) | 80/100-21 51M |
| Tire Size (Rear) | 110/90-19 62M |
| Tire Pressure | 1.0 bar / 15 psi (Front & Rear) |
Engineering Highlight: The Evolution of a Legend
While many manufacturers abandoned the two-stroke platform in the mid-2000s, Yamaha maintained the YZ 250 as a flagship of mechanical purity. The CG23C/B9U2 generation, introduced in 2022, marks the most significant ergonomic and aesthetic overhaul in nearly two decades. This model features a narrower fuel tank, a flatter seat, and redesigned radiator shrouds, optimizing rider movement while retaining the iconic liquid-cooled YPVS™-equipped powerplant that has defined the class since 1974.
Technical Performance Review
The CG23C utilizes a lightweight aluminum frame that offers a distinct balance of rigidity and flex, essential for the high-impact environment of professional motocross. The B9U2 variant benefits from updated suspension valving in the KYB® SSS (Speed Sensitive System) forks, widely regarded as the gold standard in spring-fork technology. The power delivery remains explosive yet linear, thanks to the 38mm Keihin PWK38S carburetor with a throttle position sensor (TPS), providing precise fueling throughout the RPM range.
Maintenance Guide & Fluid Specifications
To maintain peak performance and prevent premature wear of the internal components, adhering to strict service intervals is mandatory for the YZ 250.
1. Lubrication System
The transmission requires 0.75 liters of high-quality oil. MotoSpecsLab recommends Yamalube 4 (10W-40) or any oil meeting API SG and JASO MA standards. Using oil without the JASO MA rating can lead to clutch slippage under heavy loads.
2. Ignition & Combustion
The NGK BR8EG spark plug is the OEM-standard for this model. Given the high compression and 2-stroke nature of the B9U2, regular inspection of the plug for carbon fouling or electrode erosion is critical. Ensure the gap is set to factory specifications to prevent misfires during high-RPM operation.
3. Chassis & Wheel Assembly
The YZ 250 is equipped with a 21-inch front and 19-inch rear wheel setup. For optimal traction and rim protection, a standard pressure of 1.0 bar (15 psi) is recommended for both the front 80/100-21 and rear 110/90-19 tires. Adjustments may be necessary based on track density (e.g., lower for sand, slightly higher for hard-pack).
Conclusion
The Yamaha YZ 250 (CG23C/B9U2) remains the pinnacle of 2-stroke motocross engineering. By combining a proven engine architecture with modern ergonomics and world-class suspension, it offers a level of reliability and “tunability” that is unmatched in its segment. Regular maintenance of the transmission fluids and ignition system ensures this machine remains a competitive force on the track for years to come.