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YZF 250 to WR250

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Nov 24, 2002
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#1
Is there an easy way to change the power curve on a YZF250 to that of a WR250 and visa versa. I thought someone told me you just unplug a wire on the ignition on the WR to make the engine like a YZF. Is this true? any one ever done it?
Would a WR250 make a poor motocrosser? Electric start sure sounds nice sometimes.
 

Rich Rohrich

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#2
There are cam timing, jetting, ignition curve and numerous other differences between the YZF and WR models.
 
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#3
Once you've done the free mods to the wrf (throttle stop, grey wire etc) the only difference in power is cam timing and the pipe. The stock jetting is different but doing the free mods is going to require rejetting too. The wrf also has a heavier flywheel, wide ratio transmission and softer suspension which wouldnt be good on the track. If you don't need the estart, it's probably easier to get a yzf and modify it a bit to work in the woods as well as a track. That's what I did anyway.
 

miko

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#4
Originally posted by coleman
If you don't need the estart, it's probably easier to get a yzf and modify it a bit to work in the woods as well as a track. That's what I did anyway.
Doesn't the YZF have a smaller/more fragile clutch ?
A friend of a friend has a 450 YZF and according to my friend has fried
the clutch a couple of times riding in Mohab.

miko.
 
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#6
What's the "grey wire" mod? Can I do it myself?
Originally posted by coleman
Once you've done the free mods to the wrf (throttle stop, grey wire etc) the only difference in power is cam timing and the pipe. The stock jetting is different but doing the free mods is going to require rejetting too. The wrf also has a heavier flywheel, wide ratio transmission and softer suspension which wouldnt be good on the track. If you don't need the estart, it's probably easier to get a yzf and modify it a bit to work in the woods as well as a track. That's what I did anyway.
 

Rich Rohrich

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#7
Originally posted by DEANSFASTWAY
Rich did you ever spec out the cams WR vs YZ 250s?
On the cams I've measured the lobes are the same, the differences are in the phasing of the sprockets (i.e exhaust LCA is advanced about 23 crank degrees on the WR cams).
 
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Sep 28, 2003
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#8
I had an 02 WR 250F that I did all of the free mods to, as well as getting the suspension revalved and resprung and it wasn't too bad on the track. I changed the gearing, and the only other thing i didn't like was the extra weight. If only i could have kept it on 2 wheels. :|