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Are you ready to start new bike shopping? The 2008 Yamaha YZ250Fs are landing in Yamaha dealerships very soon, and Yamaha recently invited us out to take a look at their newest quarter-liter four-stroke motocrosser. Let’s dig in and see what’s new.

2008 Yamaha YZ250F

There are tons of changes, big and small, sprinkled through the '08 YZ250F.

Powerplant

The five-valve dual overhead cam engine gets a new piston that provides a boost in compression from 12.5:1 to 13.5:1. The piston skirt width has been decreased to reduce weight and friction, while boosting power.

The settings of the Keihin FCR flat-slide carburetor have also changed, and a double-taper needle replaces the single-taper needle used on the ’07. Also, the fuel screw has been richened a half-turn (from 1 7/8 to 2 3/8 turns out). A change in CDI advance timing complements the piston and carb changes.

Andy Bakken

Andy pinning it over one of the jumps at Competitive Edge.

The clutch also receives some rerouting of the oil supply, and also a boost in the volume sent to the friction plates. The plates themselves are also now use one style of fiber pack, rather than the two types of plates used in ’07. Also, the pattern has changed, and they’re said to boost both durability and allow for easier maintenance.

The tolerances in the primary drive and balancer gears were tightened in an effort to reduce backlash, which should reduce a bit of the noise coming from the engine itself.

A couple cosmetic-only changes include the magnesium cylinder head cover changed to silver. The ignition, clutch, and oil filter covers also changed, from silver to matte black.

Chassis and Components

The aluminum frame stays largely unchanged this time around, but there are still plenty of goodies you’ve come to expect, like the titanium shock spring and header pipe, Excel rims and ProTaper bars.

A big change for this year’s 250F is the swap from Dunlops to a Bridgestone M403 front, and M404 rear.

Andy Bakken

With his familiarity on the Yamahas, Andy Bakken had no problem flinging the YZ250F around. Or maybe it has something to do with him living at Nate Adams' place...

The lower triple clamp has been redesigned in an H-pattern, where material has been removed from both the top and bottom of the clamp, rather than just from the bottom. Yamaha claims that this offers a different rigidity balance, and a more even clamping surface for improved rider comfort.

There’s a new shock linkage with three percent more leverage in the beginning of the stroke, and six percent less at the end of the stroke for increased traction and a plusher feel, as well as lower (5mm) and wider (10mm) footpegs for added comfort.

In the shock there’s an enlarged compression valve port, for added plushness, as well as better damping characteristics. The rate of the shock spring has also been bumped up quite a bit, from 4.9 kg/mm, to .3 kg/mm.

Up front, the fork now uses a .45 kg/mm spring, rather than the .43 kg/mm springs used last year.

New lighter fork guards are found on all the big-bike models (YZ125, YZ250, YZ250F, and YZ450F). They provide 130 grams of weight trimming.

That same group of bikes also shares a new (you guessed it, lighter) front axle bracket. And a four-millimeter shorter upper fork tube.

Want some pedal minutia? The shift lever has been lowered 5mm, so that the center of the lever matches the level of the footpeg. Also, the brake pedal has been moved in 14mm, so that it’s less susceptible to snagging on trackside items, or any errant riders that you happen to be flying past.

Last year’s YZ250F front brake is now also being shared by the YZ125, YZ250 and YZ450F, for 300 grams (.661 pound, for those of you who don’t speak metric) of weight savings. Those same four bikes also take advantage of a newly repositioned front brake lever. The lever reach has been adjusted for riders who like to run their levers higher, and the reach is also 9mm further out than in the past.

On The Track

For photos and video, we enlisted the help of Andy Bakken, who already spends plenty of time on highly-modified Yamahas YZFs, hanging with the Motoworld Yamaha squad. He hadn’t been on a stocker in quite a while…probably since he’d picked up his ‘07s.

Overall, he seemed impressed with the modest power boost for this year, and was definitely psyched by the switch from Dunlops to Bridgestones (though he didn’t feel quite as comfortable in the corners with the new M403 front sneaker due to the sandy conditions found at Competitive Edge). He also seemed to get along fine with the stock suspension, though he’s had enough of a taste of the highly-tuned aftermarket stuff that he already had some changes in mind for the stockers.

Andy Bakken

Andy dodging the Joshua trees at Competitive Edge.

You can check out the video of him in action by clicking the link at the top of the article. There’s also a separate video with Yamaha’s Tim Olson, who runs though some of the changes.

Some years are revolutionary, like in 2001, when Yamaha was the first to introduce a competitive four-stroke into the (then) 125 class. This year’s definitely an evolutionary year for Yamaha’s 250F, but the refinements seem to make an already solid package even better.

2008 Yamaha YZ250F White

Once again, there will be a limited edition white model of the YZ250F, this time with some red accents.

{mosimage}If you want to talk about anything you've read, seen or watched in here, you can do it in the Vital MX Forums.

 

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