2014 YAMAHA YZ250F: BELIEVE IT OR NOT THE TRUSTY BUT RUSTY YZ250F ENGINE HAS JOINED THE NEW GENERATION

On Jul 16, 2013

The all-new layout of the seat, fuel tank, air box, and wrap-around exhaust system moves the bike’s mass towards the center for exceptional handling. And, in addition to an all-new appearance, the front intake layout with larger air ?lter element adds the bene?t of reduced air ?lter maintenance due to its positioning away from dirt roost from the rear wheel.

For 2014, the YZ250F is all-new, with Yamaha engineers taking everything they’ve learned along the way to create an all-new engine, chassis, suspension, unmatched mass centralization and look that, along with the YZ450F, will define the next generation of motocross bikes.

The all-new liquid-cooled, DOHC, four-valve, fuel-injected, forward-positioned straight intake, high-compression combustion chamber and rear-inclined cylinder with its straight and symmetrical intake and exhaust ports delivers more power.

The 2014 YZ250F begins with fuel injection at the heart of an all-new rearward slanted engine with the same unique front intake and rear exhaust layout that has been so successful on the YZ450F. Combined with a 4-valve head design, the engine puts out plenty of mid to top end power to get you the holeshot. A new frame, along with class-leading KYB SSS suspension make sure the YZ250F carves every corner and absorbs every bump and rut thrown at it.

The throttle body is fed by a high-pressure battery-less electric pump with excellent readability of varying temperatures and altitudes. The system provides 3-dimensionally mapped control of the volume of fuel injected and the ignition timing based on engine rpm and throttle opening. This ensures hesitation-free response and contributes to the high level of high-rpm power.

The engine’s forged two-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 new piston and rings, along with the offset cylinder configuration, reduce friction loss and contribute to quicker response.

This reversed engine layout moves the rear end of the exhaust pipe farther forward and enables a muffler position that is closer to the machine’s center of gravity. Adjustments are made in the pipe diameter in its various sections resulting in excellent exhaust pulse effect that contributes to stronger high rpm power output.

The airbox is reached by flipping the front of the seat up and removing the cover. The air filter is an over-the-cage design for 2014.

The new aluminum Bilateral Beam frame offers a superb rigidity balance and, with new front and rear suspension components and settings, 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 new layout allows the silencer to be positioned 190mm further forward, behind the right side panel, making it closer to the middle of the chassis.