Liquid-cooled, DOHC 4-valve, fuel-injected engine with the same forward-positioned, straight intake, rear-inclined cylinder, and rear-positioned exhaust layout as the YZ450F.
The 4-titanium-valve cylinder head is matched to a fuel injection system that provides power at mid-to-high rpm. The fuel injection system instantly adjusts the air/fuel mixtures depending on altitude and temperature, for a hesitation-free engine that delivers no matter the conditions.
The aluminum Bilateral Beam frame offers a superb rigidity balance and provides unmatched lightweight handling.
The exhaust pipe has an innovative layout, circling the cylinder, giving the exhaust pipe proper length for an excellent exhaust pulse effect. At the same time, the exhaust pipe has three different diameters throughout the exhaust tract, bringing out excellent power characteristics. This layout allows the silencer behind the side panel, making it closer to the middle of the bike for centralized mass for superior handling.
The layout of the seat, fuel tank, air box, and wrap-around exhaust system moves the bike’s mass towards the center for exceptional handling. The front intake layout with large air filter element adds the benefit of reduced air filter maintenance due to its positioning away from dirt roost from the rear wheel.
Accessory GYTR® Power Tuner lets owners adjust air/fuel mixture and ignition timing maps to match engine performance characteristics to the rider and track conditions in a matter of seconds with the push of a few buttons.
New for 2015:
New front fork settings offer greater performance in the mid-to-end stroke.
Quick-release quarter-turn Dzus® air box fasteners for tool-less access to the air filter.
A liquid-cooled, DOHC 4-valve, fuel-injected engine with the same forward-positioned straight intake, rear-inclined cylinder and rear-positioned exhaust layout as the YZ450F. The engine, with its straight and symmetrical intake and exhaust ports and compact, high-compression combustion chamber, delivers outstanding engine character in the highspeed range.
The adjustable fuel injection system uses a 44mm throttle body fed by a high-pressure battery-less electric fuel pump. This ensures optimum fuel atomization and air/fuel calibration for excellent rideability in a wide range of riding conditions. The system controls the volume of fuel injected and the ignition timing based on engine rpm and throttle opening, providing hesitation-free response and controllability.
Various detailed design measures are adopted to reduce horsepower loss. The forged 2-ring piston is light weight and is cooled by an oil spray jet. In addition, the compression ring is a single-ring design instead of the conventional two ring. This piston and rings, along with the offset cylinder configuration, reduce friction loss and contribute to quick response. What’s more, the specs for the intake/exhaust ports, cam profiles, ECU, carburized crank, optimized balance ratios for the crank web, transmission, clutch design, and other features, all work together to create the YZ250F’s outstanding engine character with power output in the high-rpm range.
As with the YZ450F, an innovative exhaust pipe design is adopted to increase mass centralization and improve power development characteristics. This layout moves the rear end of the exhaust pipe farther forward and enables a muffler position close to the center of the mass. Adjustments are made in the pipe diameter in its various sections resulting in excellent exhaust pulse effect that contributes to high rpm power output.
The compact wet sump lubrication system with piston cooler spray jet maintains excellent engine durability and eliminates the need for an oil tank, which lowers engine weight. This creates a more compact engine that contributes to mass centralization and unmatched handling.
The transmission and shift mechanisms reduce drive-force loss during gear changes and produce smoother shift operations and surer shift action.
The aluminum muffler is positioned closer to the machine’s center of gravity as it is almost completely hidden by the side number plate. The layout contributes to centralized mass for a lightweight handling feeling.
The front suspension has proven KYB® air-oil separated forks with stiffer fork springs, new valving and a new fork outer tube to improve performance in the mid-to-end stroke and aid fork bottoming resistance. The rear suspension also features settings optimized for ideal damping characteristics to match the chassis dimensions.
The large diameter 22mm front axle and top triple clamp increases rigidity for excellent handling and front end feel. The handlebar mounts are rubber mounted to improve comfort and reduce handlebar vibration.
The air filter is positioned away from the rear wheel which means less maintenance for the rider.
“In-mold graphics” technology is a method in which the graphics are molded into the radiator shrouds for improved decal durability and reduced scratches.
Riders have a choice of two color options: Team Yamaha Blue/ White or White/Red.