Since their original introduction, Yamaha's 4-stroke off-road bikes have grabbed a significant part of the market while enjoying huge racing success. The Japanese manufacturer is investing massively in motocross-type machines with the development of new 4-stroke engines that keep raising the bar for performance and low emissions.

The 2009 Yamaha YZ250F is no exception. Year after year, this model gains power and efficiency to offer extreme riders cleaner 4-stroke powerplants delivering more and more the type of performance associated with 2-strokers. Their power-to-displacement ratio is impressive, while their construction is lighter and less complex than that of old 4-stroke engines.

The 2009 Yamaha YZ250F is no exception. Year after year, this model gains power and efficiency.

More subtle yet equally powerful
Benefiting from minor styling revisions for 2009, the YZ250F naturally retains its most successful attributes (stylish design, light weight, agility and easy riding dynamics) while offering significant technical upgrades. Yamaha tweaked the engine to deliver a generous, linear torque curve over an extended rev band while high-rpm efficiency increases maximum power. On the other hand, the YZ250F has to meet countless requirements by the various organizations that rule motocross racing (FIM, AMA and CMRC). Yamaha engineers therefore worked relentlessly to combine the performance of their machine with these stringent noise and emission standards.

For instance, they revised the exhaust header pipe (now made of titanium) by giving it a specially-shape angle and pairing it to a 4-stage expansion chamber and a longer muffler. Some will deplore the odd shape of the unit, which overloads rear-end styling, even though this upgrade compromises neither power nor torque.

In an effort to further boost efficiency, engineers recalibrated the CD ignition system to optimize timing precision based on the engine speed so as to deliver quicker accelerations. Elsewhere, new magnesium covers for the cylinder head and clutch help reduce weight. Their color has been changed to matte black for a richer-looking package.

Some will deplore the odd shape of the unit, which overloads rear-end styling.