YMA is pleased to announce the release of the all new 2014 YZ250F aimed at taking the quarter litre motocross class to the next level.

Design goals of the new machine are increased power and optimal handling. The reverse-engine layout that has proved so successful on the 450 was selected to achieve these goals.

The new engine also features a fuel injection system that gives a great throttle response and doesn't need to be set to temperature or altitude like a carb does.

By positioning the intake in front and inclining the cylinder to the back, the intake tract is straighter. This gives a boost in performance as well as a unique style for the bike. And it has great merits for mass centralisation too, which radically improves handling.

"Due to the good mid range power, the bike is nice and friendly to ride, not only for the racer but also for the average rider. The new engine has an easier to use power band, and revs fully on to its top end when you accelerate out of corners" says tester and former World MX Championship rider Erik Eggens.

Other important new performance features include

  • A more compact combustion chamber design with DOHC, 4-valve head and narrower valve angle
  • A new two-ring piston ring design - with only 1 compression ring and 1 oil ring - which is lighter and has less friction, for less hp loss
  • Offset cylinder. By offsetting the cylinder from the centre of the crankshaft, friction losses are further reduced. This is because at the moment of greatest combustion force, the conrod position is straighter- under the piston and the piston is not pushed into the cylinder wall so strongly. This system was launched on the 2010 YZ450F and is now incorporated in the YZ250F as well.

The new engine allows accessory Yamaha Power Tuner connectivity. Easy to use and without the need to bring a PC to the track, the handheld Power Tuner lets riders adjust ignition timing and fuel injection and check maintenance items like engine hours.

The power delivery character of the bike can be set to suit different surface conditions, or to personal taste. It also allows re-adjustment of the engine if accessories like an aftermarket muffler, or GYTR performance parts are fitted.

Mass centralisation
The development team has made the new 250F smaller, lighter and easier to use. The reversed engine layout also helps with concentrating the heavy masses around the centre of gravity. The following changes have been made:

  • New air cleaner, which is a relatively light component, is in a high and forward position
  • The fuel tank is moved rearward and sits in a low position in the frame where the fuel level has a smaller influence on the handling
  • The muffler is moved forward. The exhaust pipe, which needs a certain length for good low and mid range torque, winds around the cylinder head like a snake, again centralising weight
  • In addition to this, many smaller components like the fuel pump are located at the centre of the machine. All these details improve handling.
  • Thanks to the new frame and the continued search for lighter components, with the shapes of parts throughout the machine shaved down as much as possible to reduce weight, the handling is improved even more.

Chassis features
Though it may look similar, the main frame is an all new construction. This is not a simple aluminium frame like some other manufacturers make. It is created using 10 different types of forged, cast and extruded aluminium parts that are welded together into one unit with outstanding strength, rigidity balance and shock absorbing capacity that contribute to superior cornering performance.

Because on a motocross bike it is important to have the right amount of flex versus rigidity, some parts have a very complex shape. For example the tank rails are constructed by hydro-forming, which allows the thickness of the upper, lower, right and left portions to be different.

An increased handle crown rigidity, combined with a larger front axle (from 20 to 22mm) helps to aim for and trace lines through turns at will.

Refined front and rear suspension settings with new inner tubes and revised spring specs give better stability and better ground contact.

The new, slimline body design with minimal plastic body parts and a thinner radiator design saves weight and makes you feel more at one with the bike than ever.

Erik Eggens explains the benefits of the new chassis:

"The handling of the bike is very stable. This is typical strong point of Yamaha. Not only on the straight, with obstacles like ruts, square bumps and jumps, but also inside a rut it remains very stable and you feel confident that you have control over the front wheel."

"Also on entering the corners, where other bikes are nervous and don't find enough grip, you can let the bike turn in and the front will follow its track. Turn after turn after turn. And because of the more compact and lighter body, the bike can be leaned into a turn more quickly. Because the bike is so sensitive, you can 'feel' the ground very well, you get a very direct feedback for the surface and for how the grip conditions are at any point of the track."

Practical details

  • Air cleaner box is easy access
  • Transmission and gear shifting mechanisms have been redesigned for smoother and quicker shifting
  • Graphics on the bike are not stickers but a new 'in-mould' design for greater durability
  • The fuel tank can be lifted up and rotated 180º to rest on rear frame, without disassembly of hoses - for easy maintenance access
  • Handlebars are rubber mounted for less fatigue when riding and, with less vibrations coming through, a better 'feel' of the front wheel
  • Muffler body is bolted instead of riveted, for easier maintenance
  • Fuel tank capacity is increased to 7.5 litres (from 6.4 litres) for longer motos
  • The bodywork is minimal, with a slimline design and the clean line on top of the seat allows you to shift your weight around on the bike easily without any barriers - not even a fuel cap