The truth about 250cc two-strokes is that they are wonderful pieces of racing machinerytechnically advanced, lightweight, blazing fast, cheap to maintain, and capable of being worked on with backyard tools. All of that is undeniableas is the fact that the modern motocross two-stroke can be found in the encyclopedia right next to the now-extinct dodo bird.
Of the four Japanese manufacturers, Yamaha is in the catbird seat when it comes to two-strokes. They own the two-stroke market. When they introduced their revolutionary plug-and-play aluminum frame in 2005, Yamaha took a commanding lead in the world of two-stroke motocross bikes. And as a result, they have actually gained sales and market share while the KX, CR and RM began to look long in the tooth.
The problem with being the leader of the two-stroke pack is that from a pizzazz point of view, you are the leader of the duds. It’s not that two-strokes can’t win races, or that many people wouldn’t go faster on one than on a comparable 450 four-stroke, it’s just that no one wants to buy one. That’s a shame, because if the AMA hadn’t given four-strokes such an enormous displacement advantage, we’d all be clamoring to buy a 2007 Yamaha YZ250.
Maybe, just maybe, some of us are smart enough to do it anyway. The MXA wrecking crew took a close look at the 2007 YZ250…and we liked it.
Q: DID YAMAHA MAKE ANY CHANGES TO THE 2007 YZ250?
A:Yes. Yamaha made five changes.
(1) The thickness of the inner and outer fork tubes has been changed to feed more flex into the front end of the YZ250. Additionally, there have been damping changes to improve the feel and lower the overall weight of the fork.
(2) Several key pieces of the Kayaba shock absorber have been changed from steel or brass to aluminum. The valving has undergone some modest changes.
(3) Last year’s 7/8-inch Renthal bars have been replaced with 1-1/8 inch ProTaper Contour bars.
(4) A new jet needle in the 38mm Keihin PWK carburetor boosts bottom-end and mid-range response.
(5) Lighter bolts are used throughout the chassis to reduce weight.
As a result of these changes, the 2007 YZ250 is one pound lighter than the 2006 model.
Q:IS THE 2007 YZ250 ENGINE FASTER THAN THE ?06 ENGINE?
A:Of course not. It is identical to the 2006 engine (and will most likely be the 2008 engine, also).
Q:DOES THE YZ250 HAVE THE BEST TWO-STROKE ENGINE IN THE SPORT?
A:Yes. It has the broadest, easiest-to-use and most adaptable powerband of any 250cc two-stroke.
Q:WHAT IS THE CHEAPEST WAY TO IMPROVE THE 2007 YZ250 POWERBAND?
A:Add one tooth to the rear sprocket. It will punch up the acceleration in second gear and bring third into play sooner. Faster riders, featherweight riders and fast tracks work best with the stock gearing.
Q:WHO MAKES THE BEST YAMAHA YZ250 PIPE?
A:Pro Circuit makes the best exhaust pipe for the YZ250, and they earned that reputation by making pipes for Chad Reed when he raced a YZ250 two-stroke. Pro Circuit makes two versions: the Platinum 2 for torque, and the works pipe for mid-and-up. Every MXA test rider opts for the works pipe.
Q:MOTO TASSINARI OR BOYESEN RAD VALVE?
A:The MXA test riders have raced with both the Moto Tassinari VForce3 and the Boyesen RAD Valve, and the simple truth is that they both work. If you favor stronger midrange, you might go with the VForce, while the RAD Valve offers the ability to get a potent mid-and-up hit (if you remove the stock 5mm spacer plate). Both reed valves work so well that we have to assume that the stocker has some flaws. Boyesen can be reached at (800) 441-1177 and Moto Tassinari’s phone number is (603) 298-6646.
Q: WHAT ABOUT THE JETTING?
A:In the past, Yamaha played their jetting game very close to the vest. On a warm day it was perfect, but in cold weather (or under a load) it tended to go lean. We think that Yamaha has solved that problem by replacing last year’s N3EJ with an N3EW needle. This is the optional needle the MXA test crew ran last year whenever we heard pinging (which came with aftermarket pipes, changes in temperature or deep loam). This was a good move by Yamaha.
Here are the stock YZ250 jetting specs:
Main Jet: 178
Pilot Jet: 50
Clip: 2nd from top
Air screw: 1-3/4 turns out
Q: ARE THERE ANY CHANGES TO THE YZ250’S ALUMINUM FRAME?
A:No (other than the bolt changes).
Q:HOW GOOD ARE YAMAHA’S KAYABA SSS FORKS?
A:All you have to know about Yamaha’s SSS forks is that they work very well. In truth, they are the best suspension units on the showroom floor.
If you must know the reason for their prowess, it all comes down to Yamaha’s engineers making a seismic shift in their damping theories between the AOSS forks of 2005 and the new SSS forks of ?06 and ?07. At the most basic level, there are two types of damping: position-sensitive damping and speed-sensitive damping. Almost every fork made is about 70 percent position-sensitive, which means that the damping is dictated by where the fork’s piston is positioned inside the cartridge rod. In simple terms, the farther the piston moves down in the cartridge rod, the stiffer the damping.
Yamaha’s SSS forks are 90 percent speed-sensitive. Speed-sensitive damping gets its name because the damping rate is determined by the speed at which the piston moves though the cartridge rod. It’s different, but it works. That’s all that matters.
Q:WHAT WAS OUR BEST FORK SETTING?
A:For hard-core racing we recommend this fork setup:
Spring rate: 0.43 kg/mm
Oil height: 135mm
Compression: 12 clicks out
Rebound: 10 clicks out
Fork leg height: level
Q:IS THERE A BETTER FORK OFFSET FOR THE YZ250?
A:No. The MXA test crew has tried all of the popular offsets and feels that the stock 25mm offset is about the best combination of stability and accuracy possible. We do change the offset on the YZ-Fs, but not on the YZ250.
Q:WHAT ABOUT THE REAR SUSPENSION?
A:The shock on the 2007 YZ250 is a works shock. It has a jumbo-sized 18mm shock shaft, the internal parts are Kashima-coated to reduce friction, and the shock spring is titanium. The Ti spring is high-quality, aircraft-grade, American-made titanium wire that is shipped to Japan for coiling.
We used to recommend stiffer shock springs for riders above 180 pounds, but we think that the 2007 shock works very well for riders up to 200 pounds.
Q:WHAT WAS OUR BEST SHOCK SETTING?
A:For hard-core racing we recommend this shock setup:
Spring rate: 4.9 kg/mm
Race sag: 98mm
High-compression: 1 turn out
Low-compression: 11 clicks
Rebound: 9 clicks
Notes: Yamaha’s high-speed compression clicker (the large dial) is very sensitive to adjustment. Make small (1/8 turn) changes. Use the high-speed adjuster to set the bike’s fore/aft bias at speed. National-speed riders and heavyweight contenders will need to move up to a 5.0 kg/mm spring.
Q:HOW DOES THE YZ250 HANDLE?
A:The YZ250 is a stable-platform machine. It
doesn’t have any superlatives except that it remains amazingly neutralwhich allows the rider to work with it.
It is uncannily accurate at turn-in, and it requires almost no mid-turn corrections from center-out to exit. It doesn’t impose its will on the bike’s arc at any time. It is putty in the hands of a good rider. It has just enough of everything to make it a terrific all-around package.
Q:CAN YOU GET THE 2007 YZ250 IN DIFFERENT COLORS?
A:Not from Yamaha. Although Yamaha makes blue, yellow and white plastic for the YZ-Fs, the OEM YZ250 plastic is only available in blue. Luckily for the fashion conscious, One Industries offers yellow plastic at (619) 263-9880, Acerbis has black and white kits at (800) 292-5874, and UFO offers black and white versions at (815) 756-3588.
Q:WHAT ARE THE MUST-HAVE AFTERMARKET PARTS FOR THE 2007 YZ250?
A:We don’t have a lot of wish-list items for the YZ250. It’s fairly dialed in from the factory, but here are the things we would change.
Grips: Given their druthers, four out of five MXA test riders choose soft Renthal Kevlar grips. None choose the stock YZ grips.
Footpegs: We love Lightspeed footpegs, although we don’t go whole hog for the Ti models, but spend half as much for the identical stainless steel pegs ($99 versus $199). This is the same peg that Team Yamaha uses. Lightspeed(714) 990-5767.
Brake cable clamp: Yamaha’s brake clamp is an ode to legalese. It is an overbuilt steel monstrosity. Luckily, DR.D makes a $29.95 CNC-machined aluminum front brake hose clamp that weighs half as much, is twice as small, and looks better.
Triple clamp: Although the MXA wrecking crew likes the stock fork offset on the YZ250, we do prefer the RG3 four-post triple clamp to the stocker. The RG3 clamp resists twisting and lessens vibration. It is our favorite top clamp and can be ordered in blue, machined, gold or military gold anodizing (in 7/8 and 1-1/8 inch sizes). The retail price is $289.95 at (714) 630-0786.
Q:WHAT DID WE HATE?
A:The hate list:
(1) Plastic: You can tell how important the two-strokes are to the Yamaha marketing department by the fact that they don’t get the 50th or 51st Anniversary colors.
(2) Rear brake pedal: For some reason it was tucked in too much. We bent it out to make it more accessible.
(3) Titanium footpegs: The stock footpegs are made out of Ti. They barely save enough weight to offset how heavy the bogus front brake hose clamp is.
Q:WHAT DID WE LIKE?
A:The like list:
(1) Suspension: We love Kayaba’s SSS concept. It works great.
(2) Handlebars: We had no complaints about the 7/8 inch Renthals from 2006, but Yamaha wanted to switch to one supplier, and since the YZ-Fs came with oversize ProTapers, now the YZ250 does also.
Q:WHAT DO WE REALLY THINK?
A:If we could build a bike that, compared to the best four-stroke made, weighed 13 pounds less, made double the horsepower per cc, started on the first kick, could be rebuilt for under $150, had very few moving parts, and never stalled in a cornerwe’d have the 2007 Yamaha YZ250. It is a great bike…looking for a buyer.