| Feature | Specification |
|---|---|
| Production Years | 2010 (XAF) – 2011 (YBF) |
| Engine Type | 249cc Liquid-Cooled 4-Stroke Single |
| Oil Requirement | SAE 10W-40 (JASO MA/MA1/MA2) |
| Spark Plug | NGK CPR8EB-9 (0.8–0.9 mm gap) |
| Tire Size (F/R) | 80/100-21 / 100/90-19 |
| Starting System | Kick-start (Capacitor Discharge) |
Engineering Highlight: The 2011 KX250YBF marked a watershed moment in motocross history as the first production 250cc Kawasaki to feature Digital Fuel Injection (DFI) and the revolutionary Showa Separate Function Front Fork (SFF). The SFF system decoupled the damping and springing duties—placing the spring in the right leg and the damper in the left—drastically reducing friction and simplifying tuning for professional racers.
Technical Overview: The Evolution of Power
While the 2010 (XAF) model was the pinnacle of Kawasaki’s carbureted 250 range, the 2011 (YBF) transition to fuel injection redefined the power curve. The YBF utilizes a 43mm Keihin throttle body that eliminated the bogging issues common in hard landings. This era of KX 250 F is characterized by its high-revving nature and a chassis designed for aggressive cornering geometry.
Lubrication and Engine Health
Maintaining the 249cc high-compression engine requires strict adherence to oil volumes. For a standard oil change with a filter replacement, the engine requires 0.8 Liters. If the filter is not removed, 0.7 Liters is sufficient. For a completely dry engine after a rebuild, exactly 1.0 Liter is required. We recommend 10W-40 oils meeting JASO MA2 standards to ensure the wet clutch operates without slipping under high thermal loads.
Chassis and Suspension Tuning
The transition to the SFF forks on the YBF model allows for easier preload adjustment via a dial on the fork cap. Tire pressures should be maintained at 1.0 bar (15 psi) for both front and rear to balance traction and rim protection. The 80/100-21 front and 100/90-19 rear tire configuration remains the industry standard for providing the necessary feedback during high-speed berm transitions.
Electrical & Ignition
These models are kick-start only and do not utilize a traditional lead-acid battery. Instead, they rely on a large capacitor to provide the necessary voltage for the DFI system and ignition. The spark plug choice is critical; the NGK CPR8EB-9 must be gapped precisely to 0.8–0.9 mm to ensure consistent combustion and prevent fouling during low-speed technical sections.
Maintenance FAQ
How often should I change the oil?
Under racing conditions, oil should be changed every 6-10 hours of operation. For casual trail riding, this can be extended to 15 hours, though MotoSpecsLab recommends frequent changes due to the small oil capacity.
Does the 2011 model require a battery for the EFI?
No, the system is designed to be battery-less. The ECU and fuel pump are powered by the stator and a capacitor during the kick-starting motion.
What is the benefit of the SFF fork?
The Separate Function Fork reduces weight by using only one spring and allows for more precise damping control and easier maintenance compared to traditional twin-chamber designs.