2008 Yamaha YZ250F

You would think that Suzuki, Kawasaki, Honda and KTM would show a little respect. You would think that Yamaha would get some morsel of credit for creating the 250F class and giving everyone else a new market to sell motocross bikes. You would think that they would all back off and let Yamaha enjoy the fruit of its research and development for a few years.
Fat chance. From the moment that the other manufacturers got off their collective behinds and invaded the 250F class, it’s been World War Four. Yamaha barely had time to catch its breath before being forced back into the trenches to play catch-up in the class it invented. The 2006 YZ250F was radically redesigned with a new chassis and a significantly changed motor. It wasn’t enough. The 2007 version was fine tuned. It still wasn’t enough. Now the 2008 model is here, and Yamaha is tired of reinventing the bike. Instead, the engineers focused only on the YZ’s weakest points.

Not very much. Yamaha’s motor men drilled for more torque by means of a new piston and more compression. The compression ratio went from 12.5:1 to 13.5:1, a change that usually would mean less rev. Yamaha dealt with this by lightening the piston. There are also changes in jetting (a new double-taper needle), changes  to the clutch (new oil passages and plates) and changes to the primary gears (closer tolerances).
Yamaha was a little skimpy on chassis changes, too. The most significant difference is that the bike is stiffer. The fork springs have been bumped up from 0.43 kg/mm to 0.45. The fork’s axle carrier and the profile of the fork tube at the seal head have been changed along with mild oil flow alterations. The lower triple clamp is new-it kind of looks like it’s upside-down. In the rear, there’s also a stiffer spring (from 4.9 kg/mm to 5.3) and a change in the linkage. Both front and rear brake pedals have been reshaped and there’s been a switch from Dunlop rubber to Bridgestone. If you’re looking for the major redesign just because that’s what we have seen almost every year, you’re going to be disappointed. If you’re familiar with last year’s YZ250F and know what it really needed, you’ll probably be happy.

The 2007 YZ250F would have been a great bike in a vacuum. Yamaha had solved the top-end drama, and the new frame had proven itself. But if you compared it to the Honda CRF250R, two shortcomings were plain. It was slower and harder to turn.
With just the increase in compression, the Yamaha motor has a different personality. It pulls down low. That makes it  super easy to ride by 250F standards. You don’t actually have to scream it. You probably should scream it, but if you’re the type of rider who would rather use throttle control than constant dabs on the clutch, the YZ might be the only 250F that suits your riding style. Compared to the 2007 Honda, the YZ still doesn’t have a hard hit; the power is much more gradual, and that makes it seem a little less hard-edged. But the YZ has more real pulling power on the bottom. When the bike is under a load going uphill or on loose ground, you can pull a taller gear than you might think.

At higher revs, the Honda probably makes a little more power. But we should also point out  that the Yamaha is less noisy. Yamaha seems to be much more serious  about keeping sound levels under control than any other company. Honda’s twin-pipe technology has yet to deliver the sound benefits that Yamaha has managed with its conventional pipe, and we don’t yet know how the mechanical muffler on the 2008 YZ450F will perform-we’re guessing it will be good. If you really need that little bit more mid-to-high punch on the YZ250F, it would be easy to go to the aftermarket pipe builders to find it. But if you give the stocker a chance first, you might be surprised at how well it works for the dB level.

The other issue that test riders had with the last YZ250F has been addressed with the rear suspension linkage and spring rate. The Yamaha sits up higher in its travel. Even though we set the preload at the same level of sag as the 2007 version (about 96mm), the bike holds itself up more in the rear, which gives it slightly better cornering manners. The YZ’s strongest point is its stability going into turns. Where the KX250F and the CRF like to dance around in the chop that immediately precedes most corners, the Yamaha is unflappable. It stays right on the line that you choose. But you have to stay with the Yamaha all the way through the turn. If you hesitate, chop the throttle or just aren’t riding as aggressive as you should, the bike likes to stand up. This is very different from a Honda, which doesn’t care how hard you ride. The CRF still turns with less effort than the YZ for novices and intermediates. At the expert level, there’s very little objective difference.

Aside from the change in cornering manners, the stiffer suspension has one significant impact. The bike is more suited for heavy riders than ever before. If you weigh as much as 190 pounds, you should be able to get away with the stock springs.  Conversely, if you weigh  less than 140 pounds, you might have to get softer springs, particularly in the rear. The KYB shock has a lot of useful adjustability, but you can only go so far with clickers.

Now that fuel injection is looming on the horizon, it seems like we’ve finally got four-stroke jetting figured out. The Keihin FCR carb is absolutely flawless. The bike starts easily, never flames out, and runs clean. EFI systems now have a very high mark to meet. We can’t complain about the brakes, the clutch or the shifting, either. Even the rider’s compartment, which has been very cramped on Yamahas in the past, is roomy enough for guys up to six feet tall.
So we really don’t have any major issues with the YZ when ridden by itself. That’s kind of how we felt last year, too. The real challenge for the bike will be when it faces the new Honda and Suzuki for 2008. The 250F class is fierce and cruel, and if you aren’t moving forward at a fairly significant rate, you might find that you’re really moving backwards. o

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