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YZ 2004 Models: Faster, stronger and lighter

image Fukuda-san is responsible for the development of the entire YZ range in the factory in Japan

The new 2004 off road models have many detail improvements. Don't look at the obvious, have a glance deeper down behind their bodywork.

"When we rolled out the first YZ 400 F back in 1998, the off-road world was taken by surprise. We got lots of attention. Same happened when we launched the YZ 250 F in 2001. Since then we had tons of improvements both on our four stroke line as well as on our two stroke bikes. People often are blinded by the light of totally new machines and often overlook the real technical development, which goes into our bikes every year," says a dedicated project member.

No gimmicks
Project Leader Fukuda adds: "We have concentrated on a serious development in our off-road range and are not wasting our time in gimmicks to attract attention." The project member explains further: "Take the YZ 85 for example. I am asked quite often, why we have not introduced a Power Valve to it. The answer is simple- we have considered it, but found out that the limited space in the relatively small 85 cc cylinder would result in a drop of top end power, without significant increase in mid range. The valve in this small displacement cylinder would be more of a PR exercise than a real technical improvement. I am convinced the bike is the best in its class."

image YZ 85: no gimmicks, the 85 cc bike is a serious competition machine

YZ 85: Indeed stronger than ever
The little Motocrosser has seen detail improvements that will make it simply better, like:

  • Improved clutch
  • Higher rigidity rear fender
  • New chain guide
  • Tank material changed
  • Brake master cylinder from YZ 125
  • Reinforced gear box
image YZ 125: serious development on engine and chassis makes it class leading image image

YZ 125: Evolution
Fukuda continues: "The YZ 125 has undergone small but significant changes too. Most effective was the modification of ports in combination with the increase of exhaust body tail pipe and silencer. This has given us a real boost in midrange power. This is the strongest 125 we ever had. It is very pleasant to ride, but it will stretch your arms when you pull the throttle."

ENGINE

  • Shape of Exhaust and scavenging ports changed
  • Silencer pipe diameter increased (25,4xt1.0 to 27,0xt1.0)
  • Carburettor settings modified
  • Ignition coil changed to improve performance

CHASSIS

  • New larger diameter 48mm front fork inner tube ('03 = 46mm)
  • Special low friction 'Kashima' coating on front fork outer tube
  • Newly designed triple clamps
  • Modified rear suspension linkage and bolt
  • Revised rear shock compression damping valve settings
  • New seat with high-grip frosted surface
  • Redesigned front brake master cylinder diaphragm
  • New larger front brake hose guide
  • New lightweight titanium footrests
  • New WR-style fuel tank breather hose fitting
image YZ 250 image
YZ 250
YZ 250 received the same chassis improvements as shown above for YZ 125. In addition also midrange power was improved by a modified YPVS valve assembly and a new CDI unit.
image YZ 250 F: the 4 stroke racer has seen 3 years of constant development and is the most refined machine in its class image image

YZ 250 F: the 3 year evolution pays off
"Next to the chassis improvements which were applied throughout the range from 125 to 450 cc, we paid attention to engine performance on the 250 four stroke. To increase throttle response and overall performance we further reduced friction and pumping losses inside the engine. When you ride the bike you realise, that our 3 years of experience with this high performance four stroke has paid off. The YZ 250 F is the most refined in its class," explains the European project member.

Engine modification on YZ 250 F:

  • Newly designed low-friction cylinder with reduced skirt size
  • Revised crankcase design to reduce pumping losses
  • New lightweight titanium exhaust assembly
  • New weight-saving aluminium oil lines
image YZ 450 F image image

YZ 450 F: Spin off from world championship machine
The experience gained in world championship motocross racing feeds back to the production bikes. Stefan Everts gained the title in 2002 for the second consecutive time on the four stroke factory machine.

With this experience in mind the engineers made some engine modifications such as:

  • Revised carburettor settings
  • Modified CDI with remapped ignition timing
  • New clutch housing
As a matter of course, similar evolution was brought to the Enduro versions WR 250 F and WR 450 F.


Photo Gallery: 2004-YZ85

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Photo Gallery: 2004-YZ125

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Photo Gallery: 2004-YZ250

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Photo Gallery: 2004-YZ250F

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Photo Gallery: 2004-YZ450F

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