The 2010 Yamaha YZ450F is not a bike that was released into a vacuum. There was more pre-release publicity about the 2010 Yamaha YZ450F than about any other bike in the history of the sport up to that time. If you don’t know what Yamaha changed for 2010, then you aren’t getting very good internet reception in your cave in Bora Bora. This bike is the byproduct of a few years of intense R&D testing and more than a modicum of Gyro Gearloose engineering. Yamaha threw a lot of surprises into a single package. It may be true that it didn’t all fit, but you have to break a few eggs to make an omelette.

Q: IS THE 2010 YZ450F FASTER THAN THE 2009 YZ450F?

A: Yes, but let’s not order a plaque for the wall just yet. The 2009 Yamaha YZ450F was an easy target. It had been dumbed down with the atrocious ice-cream-cone muffler and blessed with mellow cams. The best accolade that the MXA wrecking crew could give the 2009 YZ450F was, “The power is easy to use, but it is not a powerband worthy of a motorcycle sold as a race bike.” Hardly a rousing review.

Thus, the new, fuel-injected, downdraft, four-valve 2010 YZ450F engine  is night-and-day better than its older five-valve brother. In a head-to-head comparison, the 2009 has nothing on the 2010 YZ450F across the complete range of the powerband. Off the bottom, the 2010 engine is much stronger (almost guaranteed when you fuel inject a 450cc engine). Additionally, the new engine pulls harder through the middle and produces considerably more horsepower than its predecessor.

IF YOU DON’T KNOW WHAT YAMAHA CHANGED FOR 2010,THEN YOU AREN’T GETTING VERY GOOD INTERNET RECEPTION IN YOUR CAVE IN BORA BORA.
THIS BIKE IS THE BYPRODUCT OF A FEW YEARS OF INTENSE R&D TESTING
AND MORE THAN A MODICUM OF GYRO GEARLOOSE ENGINEERING.

Q: HOW WOULD WE DESCRIBE THE 2010 YZ450F’S POWERBAND?

A: Does the word “typical” seem too pedestrian. This is a cut-from-the-same-cloth fuel-injected motocross powerband. It shares most of its powerband traits with the RM-Z450, CRF450 and KX450F. It’s snappy, quick and responsive off the bottom. It doesn’t hesitate once the throttle is moved, and it makes the word “burble” as archaic as using “dames” to refer to women.

Carbureted bikes have different and distinct personalities from fuel-injected bikes. A carb can make a bike hot tempered, cold-blooded or psychotic. Living with Keihin FCR carbs on a day-to-day basis was often a case study in patience. They can be very good and they can be very bad‚ but they are always unique.

Fuel-injected bikes don’t have personalities. They are automatons. Their personalities, if you can assign such human characteristic to machines, are controlled by the electronic nebula of the ubiquitous black box. There is no variation allowed in a fuel injector’s electronic master control.   EFI-controlled throttle bodies have one thing in common‚ and that is that they have everything in common.

So, we would describe the powerband of the 2010 YZ450F as typical of all the fuel-injected motocross bikes of the 21st century.

Q: HOW DOES THE 2010 YZ450F RUN ON THE DYNO?

A: Maximum horsepower on our 2010 YZ450F was 53.88 ponies. Maximum torque was 33.95 pound-feet. For comparison purposes, our 2009 YZ450F reached 49.54 horsepower and produced 32.62 foot-pounds of torque. 

Yamaha was so proud of the 2010 YZ450F that they spent endless hours cutting the bike into chunks to make it into a see-through bike.

Q: HOW QUIET IS THE NEW MUFFLER?

The Tornado exhaust pipe was designed to keep heat away from the shock body

A: Yamaha has a star-crossed history with YZ450F mufflers. Three years ago they came out with a really weird muffler that used inverted cones inside the canister to redirect the exhaust path. Everyone assumed that Yamaha’s goal was to lower the sound level (and that may have been true), but the 2009 YZ450F still pumped out 96.1 dB. Worse yet, that so-called ice-cream-cone muffler cost the YZ450F 5 horsepower in the midrange.

Thankfully, for 2010 Yamaha returned to a conventional muffler (even if the exhaust pipe is far from typical). The 2010 makes a much-quieter 94.5 dB.

Q: IS THE 2010 YAMAHA LIGHTER THAN THE 2009 YZ450F?

A: Heavens to Murgatroyd, no! With the exception of the fuel-injected Honda CRF450 (at 226 pounds), every other fuel-injected bike is a porker. The Yamaha gained 5.2 pounds. It took Yamaha five years to trim 5 pounds off of the original YZ450F, and just as with any yo-yo diet‚ the weight is back!

Q: HOW DOES YAMAHA’S FUEL INJECTION DIFFER FROM THE CRF450’s, KX450F’s AND RM-Z450’s EFI?

A: Let us count the ways:

(1) The Yamaha cylinder head was expressly designed for fuel injection, whereas Honda, Kawasaki and Suzuki just bolted the EFI throttle body on in place of the carburetor.

(2) Yamaha’s downdraft design is as close as any motocross bike has come to the idea of direct injection. The intake tract doesn’t make any convoluted moves to get to the combustion chamber.

(3) Yamaha uses a 44mm Keihin EFI. Honda has a 50mm throttle body, while Suzuki and Kawasaki use 43mm orifices.

THE YAMAHA GAINED 5.2 POUNDS. IT TOOK YAMAHA FIVE YEARS
TO TRIM 5 POUNDS OFF OF THE ORIGINAL YZ450F…AND JUST AS WITH ANY YO-YO DIET‚ THE WEIGHT IS BACK!

The intake and exhaust cams are designed to increase the valve-working angle and valve lift for all-around performance.

Q: WHAT IS UNIQUE ABOUT THE 2010 YAMAHA YZ450F ENGINE?

A: Answering this question is like shooting fish in a barrel.

Tilted cylinder. The YZ450F cylinder is tilted rearward by 8.2 degrees (given that the 2009 engine was tilted forward 4.5 degrees, that is a 12.7-degree shift).

Offset crank. It should be noted that Yamaha is not the first manufacturer to offset the centerline of the cylinder over the crankshaft, but by moving it 12mm, they take the cake for the most offset of all time.

Bore and stroke. The 2009 Yamaha YZ450F had a 95mm bore by 63.4mm stroke. The 2010 YZ450Fis decidedly more over-square, with a 2mm-larger bore (97mm) and 2.6mm-shorter stroke (60.8mm).

Four-valve head. The 2009 YZ450F had a five-valve Genesis head, which Yamaha adopted for its street bikes back in 1984. The switch to four valves started with the 2007 YZF-R1 street bike. The reason? With the five-valve design, the designers are restricted as to how much they can shape the combustion chambers. Switching to a four-valve design gives the engineers more usable area around the combustion chamber. This is most evident in the higher-compression ratio for 2010 (12.5:1 instead of the old 12.3:1).

Q: HOW DOES THE 2010 YAMAHA YZ450F HANDLE?

A: Technically (as in technologically), Yamaha has leapfrogged to the top of the heap with its new aluminum frame. This is the first Japanese-built motocross bike to attempt to harness the gyroscopic forces of the engine’s rotating mass.

The first words out of every MXA test rider’s mouths were, “This thing is light!” And, that statement is made all the more significant by the fact that the 2010 YZ450F isn’t even remotely light (it’s 5 pounds heavier than last year). Yamaha’s slavish devotion to moving every major part of the engine towards the center of gravity has paid tremendous dividends in the “feel” department. This bike feels like a feather.

Q: WHAT ABOUT THE PUSH IN THE FRONT END?

A: After years of trying Band-Aid fixes on the earlier generations of YZ450F frames, Yamaha finally went all out with the new chassis they have needed for half a decade. With the new fork offset (reduced 3mm), head angle (steepened 0.1 degrees) and weight bias (2 percent farther rearward), the new frame rolls into corners with ease.

The top-heavy feel of the old YZ450F is gone, replaced with a super-agile ability to transfer from one roll angle to the next. Thanks to the wonders of gravity, rotational moments of inertia and mass centralization, the 2010 YZ450F is better in pitch control than any other 235-pound bike. Additionally, if the front end drops over a jump, it can easily be returned to normal with a flick of the throttle.

We cannot honestly say that it feels like a 250 four-stroke in motion, but it has managed to bridge the gap between the a 250cc fighter jet and a 450cc long-range bomber.

The old push in the center of the corner is gone. Thank goodness.

Q: WHAT WERE OUR BEST FORK SETTINGS?

A: Yamaha may have built a totally new engine, fuel management system, exhaust pipe and ergonomic layout, but they didn’t need to reinvent the wheel when it came to the Kayaba SSS suspension.

Even the rear shock, which has been moved forward in the frame, maintains the exact same rising rate as last year’s bike. Thus, the 2010 YZ450F can easily be described as a revolutionary new bike with old-school suspension. No complaints, because the previous suspension was too good to mess with (except for spring and damping changes related to the new weight bias and head angle).

For hardcore racing, these are MXA’s recommended 2010 Yamaha YZ450F fork settings (stock settings are in parentheses).
Spring rate: 0.47 kg/mm
Oil quantity: 355cc
Compression: 10 clicks out (13 clicks out)
Rebound: 9 clicks out (10 clicks out)
Fork leg height: 0mm up
Notes: The 2010 Kayaba SSS forks have 10mm more stroke (from 300mm to 310mm), are 7mm longer and have 10 percent more low-speed compression damping.

Q: WHAT DID WE LIKE?

A: The like list:

(1) Oil-sight glass. Although Yamaha has a terrible reputation for putting their sight glasses in the wrong place, every MXA test rider vastly prefers a sight glass over a dipstick.

(2) Spring preload. Thanks to the backwards engine design, there is abundant access to the rear shock. Adjusting the preload, which can be extremely difficult to get to on other brands, is a snap on the 2010 YZ450F.

(3) EFI Power Tuner. Unlike Kawasaki’s and Honda’s reprogramming devices, Yamaha’s Playstation-style GYTR Power Tuner does not require a laptop computer or 12-volt battery. It is a self-contained device that allows the fuel map and ignition timing to be changed at nine different rpm/throttle positions. The retail price is $279.95.

(4) Clutch cover. On the 2010 YZ450F, Yamaha built ridges onto the surface of the clutch cover to keep the rider’s boot from scratching the paint off the cover. Obviously, the YZ45OF designers didn’t share this idea with the YZ250F designers.

(5) Sound. Although not the quietest 450cc motocross bike we have tested, the 2010 YZ450F is 2 decibels quieter than last year (and is now AMA legal).

Q: WHAT DO WE REALLY THINK?

A: The 2010 Yamaha YZ450F is one giant leap forward for techno-geeks. It is a marvel of innovation and engineering. Luckily, all that gee-whiz, Gyro Gearloose, slide-rule machinating has resulted in a bike that the typical home-schooled, slacker, wannabe moto prodigy can learn something from. This is a great bike with lots of educational value.