WHAT HAVE YOU DONE LATELY?
In 2014 the YZ rose from the dead. The carbureted,
five-valve motor was placed on a pedestal in the Museum
of Great Things That Stayed Too Long, and a new motor
surrounded by a new chassis took its place. The 250 was
recast in the same image as the 450 with its reverse, rear-ward-tilted head. Fuel injection came at last, but in the
case of the Yamaha, it didn’t add as much weight as we
had seen with other dirt bikes. The new YZ was the lightest in the class, and the success story started.
Since then, other bikes have come along that are faster
and lighter. Yamaha knew that would happen, and the
2017 YZ has received just enough attention to keep it
fresh. There are 16 changes to the new bike.
• The funnel between the airbox and the throttle body
was lengthened by 15mm.
• Both the cams and cam springs are new.
• The cylinder head is new with different port shapes.
• There’s more volume in the throttle-body joint.
• The middle section of the pipe is larger.
• New material is used for the connecting rod, which
has a slightly different shape.
• Different heat treatment is used for the engine cases.
• New mapping has been developed for the ECU.
• The clutch arm on the engine is shorter, and the cable
angle has changed.
• Five gears have been altered in the gearbox, and the
output shaft is larger.
• The lower-engine mounting brackets are now steel;
the upper ones are reshaped.
• There’s increased frame rigidity around the swingarm.
• The fork’s outer tubes are more rigid, and the valving
has been changed.
• Both footpegs are 5mm lower.
• The rear disc has new material.
• The Dzus fasteners are recessed in the airbox cover.
Individually, these changes won’t shake up anything.
But, shaking things up wasn’t the goal. Maintaining the
status quo is what you want when you’re on top of the
WHY IT STILL WINS
We used to think that peak power was the most important factor in the world of 250cc four-stroke motocross
bikes. That’s because they were so slow. The first ones
made less power than a 125 two-stroke. Not any more.
The Yamaha’s success has come despite not having the
biggest dyno number. The quality of the YZ250F’s power
is excellent. It has good low end and no hiccups all the
way to a 14,000-rpm peak. What riders like most about
the Yamaha is how it responds to throttle input. You don’t
have to twist it all the way open to make it go. It starts
moving from the first crack. Peak power happens way
up high—a little too high to give you a margin of comfort
between the happy zone and the rev limiter. You often
find yourself flirting with the 14,000-rpm cutoff point. The
good news is that this year the cutoff is gentler. Instead
of feeling like you just jerked the extension cord out of the
wall, it feels like the YZ just stops making power. If you
remember, Yamaha engineers play with this each year. It
turns out that there are many ways to keep a motor from
over-revving, and the current formula means that you can
keep screaming the motor if you find yourself in a situation
where you can’t get to the shifter.
Yamaha is the only maker that doesn’t offer you alternate maps that can be switched through the use of but-
MX TEST: 2017 YAMAHA YZ250F
Yamaha says there are 16 changes to the 2017 YZ250F.
It’s still the bike to beat.