2010 Yamaha YZ250F Revealed - Dirt Rider Magazine

2010 YZ250F Frame on the left, 2009's frame on the right

New bike season is officially in full swing with the release of the 2010 Yamaha YZ250F. We're actually testing the new Yamaha YZ250F as you read this so check back for our first riding impression later today.While you patiently wait for the story on how the new Yamaha YZ250F runs and works on the track, take a look at what it's made of with Dirt Rider's first look.Let's look at the new Yamaha YZ250F motor first.While we were expecting (hoping) for fuel injection, the 2010 YZ250F comes with a carb. Not much to complain about since the Yamaha YZ250F has been one of, if not the best carbureted bike in this class. Instead of electronics, this motor gets better breathing, lighter valve-train components, more efficient combustion and a new exhaust system starting at the cylinder head porting.Bottom end improvements range from new gear ratios and strengthening as well as clutch leverage and spring rate changes.Interestingly, the power improvements across the board are designed, and this is a direct quote, to, "Improve power while reducing noise."Here's the new Yamaha YZ250F motor in detail.-New Airbox shape
This is designed to straighten and smooth the intact tract from air filter to carb. The smoother and straighter the path from air to fire, the better-especially for fuel injection (which we expect to see next year on the YZ250F. The entire air filter is shifted to the left 10mm.-New Carburetor with new Bore Ventruri Shape and new settings
Continuing the straight-shot air management, Yamaha designed an all-new carb body. This eliminates the step in the old intake bell. The accelerator pump cam is changed for quicker fuel delivery. Also, the jetting is changed to the richer side of things. Yamaha is going for a good "torquey" feel at low RPM while delivery the best response possible under quick openings.2009 Yamaha YZ250F Jetting specs:
Main: 178
Pilot: 42
Needle: NHKR-4
Leak: 70
Fuel Screw (turns out): 22010 Yamaha YZ250F Jetting Specs:
Main: 180
Pilot: 45
Needle: NDJR-4
Leak: 70
Fuel Screw (turns out): 2.25-New Cam Profile
The YZ250F's intake cam profile is changed for better low end to mid-range power and response. The Yamaha YZ250F took a little beating in the past from the press for being a bit sleepy on the bottom. Maybe this will silent that. The cam now has 7.7mm of lift versus the 7.6mm from last year while maintaining the same cam timing. That means the valves are opening a bit more but opening at the same time-basically. There is a hard surface treatment applied to the very top of the valve stems, too. Yamaha's proven YZ250F valve durability should see an improvement with the fancy Chromium Nitride coating.-Valve Spring Retainer Changed From Steel to Aluminum
Lighter is better and with the reduced load on the spring thanks to the Aluminum retainer, the spring rate can also be lightened. The intake spring load is reduced 12% and the Exhaust spring load is reduced 9%. Reduced friction and better low-end to mid-range power and response are the goals.-Exhaust Port Shape Is Changed and Volume is Reduced
Yamaha wants its exhaust gases to have more velocity so it shrunk the exhaust port into a D-shape. Guess why. Yep, for better throttle response.-New Exhaust System
Yamaha went back to (after going away from) a two-step mid-pipe for 2010. It steps up from 45 mm to 50.8 mm right after it attaches to the frame. Further back the muffler grows 50mm and gets a reduced core diameter. Inside, the "pipe perforation pitch" (meaning the amount of holes, really) changed from 4-5mm. That means the less holes and they are farther apart. The muffler mount changed from rubber to solid metal-on-metal. All this to reduce sound without reducing power from the new Yamaha YZ250F.-Clutch Mods
Internally, the 2010 Yamaha YZ250F clutch basket center boss gets hardened material for more durability and the clutch arm ratio and clutch spring load are both increased. The result? Easier lever pull (3% easier) with stronger engagement and wider engagement area feeling. That means less herky-jerky clutch on-off action.-Transmission updates
Gear strength is increased in 3rd, 4th and 5th gears with 3rd and 4th getting a slightly taller ratio. That's like a half tooth difference on a rear sprocket. There is also some revision to the drive dog shape. Stronger, better engagement is what Yamaha is looking for here.-Ignition
Ignition mapping is changed to match all the intake and exhaust specifications for the 2010 Yamaha YZ250F.-New Compact Oil Tank
While total oil capacity in the 2010 Yamaha YZ250F is reduced to 1200ccs (down 100 from last year), the biggest change you'll see is with the smaller oil tank. Keen eyes will also catch the new position of the oil level sight glass that jumped from the crankcase to the ignition cover. The oil now drains from the back of the engine instead of the side, too.-New Radiators and mounting/hose routing
The 2010 Yamaha YZ250F radiators mount 15mm lower and 10mm farther back than 2009. Also, the hose routing changes and the mounting points increase from two to three. This makes stronger radiators without the external bracing we've seen in the past.That's the 2010 Yamaha YZ250F motor in full detail. Here's what's new with the 2010 chassis.-All new 2010 Yamaha YZ250f Frame
Yamaha stays unique with a "Bilateral Beam Frame". Unlike everyone except Europe's twin-spar full perimeter frame, Yamaha tucks their beams (spars in) to follow more closely in line with their previous offerings. The frame uses a 20-piece combination of forged and extruded components. Lateral and torsional rigidity is increased to transfer dieways shock into longitudinal shock smoothly. The idea is to take twisting and bending forces coming from side to side to flow into the straight-line or vertical line of the chassis so the suspension can deal with it. After all, that's the suspension's job.-Frame Head Pipe Position
The frame head pipe is 12mm lower and 7mm further back than 2009, changing the caster and trail dimensions. The 2010 Yamaha YZ250F has a more compact chassis putting the rider closer to the front wheel for lightweight handling and quick direction change. The YZ four strokes don't win turning competitions in our shootouts, but maybe now they will.Caster:
2009: 27.2 mm
2010: 27.5 mmTrail
2009: 117mm
2010: 120mm Continue to page 2 for more on the 2010 YZ 250...

-Engine Head Mount Changed
Instead of one center-biased head mount for the motor, the 2010 Yamaha YZ250F gets two side-oriented mounts. This is a big tuning area in frame design. Engineers at Yamaha told us that even the shape, angles and thickness of the piece of aluminum spanning from the motor to the frame makes a huge difference in the chassis balance and feel.-Suspension: Fork settings/coatings changed
KYB's Speed Sensitive System front fork is updated with new damping settings and a new fork seal shape for the 2010 Yamaha YZ250F. Also, the piston rod gets a new surface treatment and the fork protector slider is changed from plastic to steel.-Suspension: Shock Spring Lowered and Damping Specs Optimized
The big change in suspension on the 2010 Yamaha YZ250F comes in the shock department. Side-by-side the 2010 KYB shock looks a lot different than the 2009 version. Most noticeable is the lowered nature of the spring. It's 30mm lower to be exact. The lower section of the shock is modified to drop the spring. The lowering drops the weight of the spring down lower in the chassis for an improved ceneter-of-gravity feeling to the bike and makes room for the straight-shot intake tract.-Improved Ride Position
Pro Taper Bars with four-way adjustable bar mounts mount up to the 2010 YZ250F with an exclusive Yamaha bend. The handle bar mounts are 5mm taller and the footpegs match that with a 5mm boost of their own. Yamaha is trying to keep a decent range of adjustability in the cockpit and match the chassis characteristics of the new YZ 250F. The theme is light, nimble and with quick directional changes.-New Seat Shape
Yamaha's 2010 YZ250F gets a flatter and more forward seat. They claim this will be easier to transfer weight on when going from cornering to straight-a-ways.-New Fuel Tank
The new 250F from Yamaha gets a smaller, more centralized fuel tank. Capacity goes from 7.0 Liters (About 1.8 Gallons) to 6.4 liters (About 1.7 Gallons). The fuel petcock is relocated, too. The tank fits the new frame, obviously, but was designed to keep the fuel weight in the center and to minimize the weight shift as is sloshes around.-New Brake Pedal and Kickstarter shapes
These simply match the new frame.-New Skid Plate and Engine Guard Designs
A simpler one-piece design with an integrated water pump guard replaces last year's two piece unit. Also, the 2010 Yamaha YZ250F's guard is plastic instead of aluminum. Plastic doesn't affect frame rigidity like metal bolt-on plates can and the increased coverage of the one-piece unit covers the vulnerable frame rails.-New Body Styling
This is obvious but the 2010 Yamaha YZ250F uses all new body work plastic. But what you don't know is that Yamaha engineers envisioned an arrow (maybe shooting off to a distant Anime world of wonderful enjoyment and happiness with dirt bikes jumping over pink and yellow panda bears) when they laid out the molds. The bike's look is supposed to emphasize "the light weight and nimble handling character of the YZ250F". It's also a "sharp, horizontal styling movement".Also on the style-watch radar is the addition of more cool-colored metal parts. Front fork feet, spread out engine side panel coverage, triple clamps and wheel hubs all get the factory, showroom valuable black look.The 2010 Yamaha YZ250F is available in two colors: Team Yamaha Blue/White and White/Red.Now that you know all there is to know about the nw important to remember where the Yamaha YZ250F came from. It's a historic bike, as are all of Yamaha's four stroke motocross dirt bikes.Yamaha YZ250F SUCCESSES
.1ST TO MARKET WITH 4 STROKE 250F (2001 YZ250F)
.1ST TO WIN AN INTERNATIONAL RACE (2000 Final round All Japan- Ernesto Fonseca)
.1ST TO WIN AN AMA SX (2001 Anaheim 1-Ernesto Fonseca)
.1ST TO WIN AN AMA SX TITLE (2001 West Coast-Ernesto Fonseca)
.1ST TO WIN AN AMA NATIONAL (2001 Red Bud-Larry Ward)
.1ST TO WIN WORLD GP (2003 GP of Austria-Stefan Everts)Second, with so many options out there, why would you want to buy a YZ? Here's a few things Yamaha likes to point out to shoppers looking for a new Motocross bike. The 2010 Yamaha YZ250F gives you all this..ONLY JAPANESE MANUFACTURER WITH A WARRANTY.EVERY YZ IS SOLD WITH A 30 DAY WARRANTY THAT COVERS AGAINST MANUFACTURER DEFECTS. .OVER 13 MILLION DOLLARS AVAILABLE IN CONTINGENCY. EVERY YZ SOLD IS CAPABLE OF TAKING HOME ITS FAIR SHARE OF THE 13 MILLION DOLLARS POSTED IN YAMAHA CONTINGENCY. .COMPLETE PARTS CATALOG AND OWNERS MANUALS AVAILABLE ONLINE. ALL ONLINE AT YAMAHA-MOTOR.COM UNDER THE PARTS AND SERVICE TAB.Check out our first riding impressions and full tests online and in the magazine soon. Until then, dream of Pandas on dirt bikes and smile!****For more specs on the 2010 YZ250F mx bike, click here.