The Yamaha YZ250F has made a name for itself as one of the most competitive 250cc four-stroke motocross bikes. In every motocross race, this bike has proven that it has what it takes to win in all conditions, in MX and SX. For the 2021 model year, Yamaha is going even further with the introduction of the new YZ250F – featuring an improved engine, redesigned frame, new suspension setup, new brakes and advanced digital technology in this highly competitive class. Every major component of the YZ250F engine has been redesigned and improved to give the racer a real advantage on the racetrack. With a reverse cylinder head design, the engine will provide increased intake efficiency and better mass centralization. The engine’s power feel for 2021 is further improved in the mid-rpm range through to over-rpm performance with a new exhaust camshaft with a redesigned profile that reduces valve overlap. Along with an optimized fuel injection setup, the new camshaft improves the YZ250F’s mid-range character, providing a higher level of power along with improved handling. The intake system for the 2021 model is completely new and the airbox is redesigned, where the intake funnel is shortened by 20mm for a more “direct” intake. Another key change is the use of an air cleaner box cover mounted on the front of the seat. This change will increase the intake air volume and result in more power at high revs. New muffler with increased capacity installed. This new system, which is 70mm longer than the previous design, was built by Yamaha to provide smoother acceleration, especially at high revs.
The 2021 Yamaha YZ250F features a new twin-beam aluminum frame that – while looking similar to the previous design – features a number of significant changes to match the 2021 engine performance upgrades and deliver a noticeable improvement in handling feel and performance. Yamaha improves stopping power and reduces the weight of the braking system for the 2021 Yamaha YZ250F. The redesigned front caliper is 30% stiffer than before and uses larger diameter pistons and newly designed brake pads – while the new 270mm front disc results in a 16% increase in contact plate area without increasing the weight of the disc. The design of the rear brake caliper is also new, and together with the new 240mm rear discs, this system maintains the same level of braking performance with an overall weight 120g lower.
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YZ250F New Features for 2021
- Redesigned high-performance motor with stronger peak performance
- Smoother throttle response with longer over-rev feel
- Optimized exhaust camshaft design with a new profile and reduced overhang
- Idealized fuel injection settings provide higher performance
- A completely redesigned intake system increases performance at high revs
- Greater shock absorber capacity for smooth acceleration at high revs
- Stronger clutch housing for better engine performance
- Redesigned gear wheels with optimized performance and strength
- Double-sided beam frame of a new specification with an idealized ratio of strength and stiffness
- Revised front and rear suspension settings offer better handling
- Lighter and more powerful front (Ø270 mm) and rear brakes (Ø240 mm)
- Lighter handlebar crown and adjusted handlebar position
- Lighter footrests made of chrome-plated steel
- Lighter front axle shaft
- Icon Blue body and matching blue front and side plates
2017 YZ250F
Equipped with an innovative reverse cylinder head engine, the groundbreaking Yamaha YZ250F has proven that it has what it takes to take on the toughest rivals. This game-changing motocross bike powered Jeremy Martin to back-to-back AMA 250 Motocross Championships in 2014 and 2015, while YZ250F rider Cooper Webb also won back-to-back AMA 250SX West titles in 2015 and 2016. For the 2017 model year, the YZ250F benefits from a number of important technical changes, such as an all-new reverse cylinder head.
2017 YZ250F Improvements
- Increased tractive force in the mid to high rpm range
- Improved acceleration
- Smoother shifting and smoother clutch feel
- Refined handling and suspension for improved stability and control
- Improved braking performance
With major improvements to intake and exhaust efficiency, along with smoother gearshifts and a remapped ECU, the 2017-spec engine delivers a significant increase in race-winning performance. The YZ250F’s innovative reverse cylinder head with front intake and rear exhaust offers many advantages over a conventional design. These include increased intake and exhaust efficiency, as well as improved mass centralization through the use of an overhead air filter and an underseat fuel tank. For the 2017 model year, Yamaha engineers have taken this cutting-edge technology to the next level, developing a new reverse cylinder head that gives the YZ250F rider even more mid-to-high-end pulling power. To increase the flow of fresh air to the 4-valve head, the position of the intake port is increased and the diameter of the intake valve is increased. New higher-lift intake and exhaust camshafts provide increased valve lift for a stronger feel in the mid-to-high rev range – while the intake camshaft operating angle has been narrowed for better low-to-mid rev performance.
Stronger intake and exhaust valve springs are fitted to match the use of new higher-lift camshafts – and to accommodate the increased engine output, the 2017 model uses a newly designed nickel-chromium-molybdenum steel connecting rod.
A further significant boost in mid-to-high-rpm performance has been achieved by shortening the intake manifold to reduce pumping losses – and the use of a larger throttle joint between the injector and intake opening provides an increased cross-sectional area of around 5% – while its new internal design promotes better fuel vaporisation . To achieve the optimal balance of intake and exhaust, the dual exhaust ports have been redesigned and the sinuous tailpipe features a new larger-diameter front end. In addition to the larger pipe bore, this front end also benefits from larger bend radii that provide a larger internal cross-sectional area that creates a much stronger exhaust pulse effect. To match the engine’s increased performance thanks to a redesigned cylinder head and highly efficient intake and exhaust systems, the 2017 YZ250F features a newly developed ECU with revised ignition timing and fuel injector mapping. The new ECU kicks in at higher revs and features a rev limiter that provides a better over-rev feel.
