Having won last year's Dirt Rider shootout, it would make sense that Yamaha would already have an excellent base for the 2003 model. So we weren't really shocked the research and development team didn't fully redesign the machine, especially when you consider that most companies operate off of a three-year cycle before making radical and expensive changes. Plus, we assumed the factory was too busy working on the new YZ450F—and the two WR models—to do much with its premier two-stroke model.But Yamaha doesn't seem to be sitting around while other companies play catch-up. As the answers to the eight most asked questions show, it spent a lot of time refining a machine that is almost perfect.WHAT CHANGES DID ENGINEERS MAKE TO THE YZ250?
• Modified the rigidity of the frame and swingarm to improve handling and reduce weight
• Decreased the combustion chamber from 21.5 to 21cc
• Reshaped cylinder exhaust ports and raised them 0.4mm higher
• Increased crankshaft taper from 17 to 18mm and the nut size from 10 to 12mm to improve rigidity and reliability
• Made second gear slightly taller. The '02 version was 25/16 or 1:1.563, whereas the '03 version is 23/15 or 1:1.533
• Re-valved front and rear suspension
• Re-designed rear brake caliper and integrated the master cylinder for weight reduction. Piston diameter has been decreased from 12.7 to 11.6mm--saving 45 grams
• Increased rear brake caliper piston diameter from 24.5 to 27mm to make it 20 percent more rigid and improve braking characteristics
• Fuel tank is 350 grams lighter
• Revised piston material and shape in the front brake caliperWHAT EFFECT WILL THE YZ450F HAVE ON YZ250 SALES?
The new quarter-liter motocrosser will probably have very little effect on YZ450F sales. Most people who will buy four-strokes are already four-stroke owners and will simply replace old equipment when the new YZ-F makes its debut. Although both machines can get you around a racetrack in a hurry, the buying public seems to be divided when it comes to taste. There are very few people sitting on the fence, who haven't already made the change, but as four-stroke technology continues to reinvent itself at an accelerated pace, there will still be people who will explore their options more thoroughly before making a buying decision.HOW IS THE YZ250 MOTOR?
Downright killer! The engine is the highlight of the new YZ250, and it works about everywhere you would want it to. It features great off-idle response, coupled with big power throughout the midrange and top-end. Delivery is crisp and clean, and is more usable than on the '02 version. We also liked the taller second gear, which is arguably the most important gear in a transmission. We know power can still be improved by the aftermarket through cylinder porting, head mods and a performance exhaust, but it will be more difficult to get the type of gains people have come to expect. Every tester jumped off the YZ and said it was race-ready in stock form. It also makes us wonder just how much more power the manufacturers will be able to squeeze out of 250cc two-strokes in the future.WHAT JETTING WORKS BEST?
The 38mm Keihin PWK carburetor with a Power Jet and throttle-position sensor is set up really well for sea level. We tested during the early summer months when it was 80-95 degrees with minimal humidity and the 178 main, 200 main air and 50 pilot worked well with the clip in the third position from the top.