YZ250F: Finally Gets EFI, But No Air
Offering a radically different motorcycle from its previous 250cc models, Yamaha is truly swinging for the fences in 2014 in the 250F class.
No more delaying – EFI is here! Yamaha finally replaces the carb with a fuel injection system that uses a Keihin 44mm throttle body. Another huge change in the motor department is a rearward-inclined cylinder, just like the blue 450. Because of this new orientation, the YZ250F also adopts the bigger bike’s rear-positioned exhaust, forward-facing intake and wraparound header. The four-titanium-valve cylinder is fed fuel by a high-pressure battery-less electric pump for an optimum fuel/air ratio. All of these engine changes were aimed at more power, especially in the mid-to-high rpm range. Also, Yamaha got rid of the external oil tank for the YZ250F’s wet sump lubrication system.
Though the final suspension specs have not been finalized, neither bike will have an air fork. According to Yamaha, they have been testing them but don’t think they are right for the YZ-Fs just yet. So though the 250F’s suspension isn’t radically different, the chassis is. The 250 gets the same treatment that the 450 received – hidden gas cap, asymmetrical sub-frame, bilateral beam aluminum frame, narrower overall width, and larger, but lower, two-gallon gas tank. The muffler, due to the wraparound header, is closer to the center of gravity and along with the other changes mentioned works toward mass centralization, a major focus for Yamaha’s 2014 MXers. Also, because of the shorter pipe, the sub frame is shorter and lighter, again, tightening up the bikes overall mass distribution.
The 250F’s fork and rear shock have new spring specs to compliment the all-new frame and the shock’s reservoir went from horizontal to the more-common vertical arrangement. Up front, a larger 22mm front axle with a new top triple clamp increases rigidity while rubber mounted bars keep things from getting too stiff. Last of the major changes, the air filter finds a new home in front of the gas tank just like the 450F’s.
YZ450F Gets New Frame And Shares With YZ250F
In the engine department, the YZ450F gets a new cylinder head, maintaining the straight port down draft design, new intake and exhaust valves, which are enlarged and the cam profile for the intake has been modified, all contributing to improved combustion, resulting in added power. It also received a new piston, ignition timing and fuel injection mapping. The new ECU boost bottom end power plus delivers a strong feeling of power from 3rd gear up while new gear ratios also lengthen the powerband and heighten the feeling of power in 2nd and 3rd gear. Newly designed transmission and shift mechanisms aim to provide quicker, smoother shifting under power with less effort.
The exhaust pipe layout is all new and now circles the cylinder, giving the exhaust pipe proper length for stronger power. At the same time, the exhaust pipe has three different diameters throughout the exhaust tract. This new layout allows the silencer to be positioned 7.3 inches further forward, tucking behind the side panel closer to the middle of the bike which centralizes the mass for better handling.
The engine’s compact wet sump lubrication system with piston cooler spray jet eliminates the need for an oil tank, reducing engine weight. The water pump employs a plastic resin impeller for further weight reduction. The reduced size of the crankcase made it possible to mount the 450cc engine in the new frame design. That newly designed aluminum bilateral beam frame has dimensions similar to the 2013 YZ250F frame and the head pipe is moved 10mm closer to the rider than last years YZ450F frame. This gives the 450 a compact chassis.
A new layout for the fuel tank (now 2 gallons instead of 1.5 gallons) and air cleaner box gives the bike a slimmer feeling between the legs as well as positions fuel tank mass closer to the center of the bike. A new increased volume airbox allows the bike to be narrower at the radiators by 14mm overall (7mm per side) and uses a more traditional airfilter than before. Access is much easier, using only three bolts.
The proven KYB air-oil separated forks are still there with a new spec inner and outer tube, coupled with new suspension settings. The rear shock has a new reservoir location to accommodate the new gas tank while the spring spec and settings were changed to match the new chassis.
Just like the 250, the front wheel now uses a larger diameter 22mm front axle. A new top triple clamp works to increases rigidity for improved handling and front end feel. The handlebar mounts are now rubber mounted to improve comfort and reduce handlebar vibration.
If the 2014 YZ250F and 2014 YZ450F look a lot alike it is because they are. Much like other manufactures, Yamaha has gone the route of the same chassis just with a different engine. The new 2014 YZ250F and 2014 YZ450F share the exact same frame, swingarm and subframe, even the same suspension with different settings. The brakes are the same, the bodywork is the same, the triple clamps the same, you name it. Even the motor mounts are the same. Properly executed it is a great plan for everyone invovlved. It cuts manufacturing costs and makes acquiring parts that much easier. We can’t wait to start testing both of these machines!