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Old 3 Weeks Ago
Nutty's Avatar
Nutty Nutty is offline
The "One" and only
Join Date: Apr 2006
Location: Shoalhaven NSW
Posts: 11,800
YZ250 tuning tip

Re: power valve actuation on WR/YZ 250s. The problem is that the RHS segment vent was deleted by the pipe builders. I sussed this out building 250Superkart motors. The RHS valve develops an oil-film seal which delays the PV opening, a pneumatic governor of sorts.

Buy a hose and a 90 degree fitting and make the RHS PV cover vented, the same as the LHS one. You'll have to clearance the pipe with a ball-pein hammer. The fitting press-fits with some bearing mount or wick-in.

Best (and cheapest) mod ever to get the 250 going.
"Ain't no use in waking if your dreaming's done" : Pigram Bros.

Current dirtbikes: 2018 450SX, 2018 YZ250-FX
Current road bike: 2011 FLHRC-Police spec
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Old 3 Weeks Ago
BigE BigE is offline
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Join Date: Aug 2008
Posts: 283
photo would be good?
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Old 3 Weeks Ago
eXc eXc is offline
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Join Date: Feb 2003
Posts: 2,069
interesting idea. Have you done this on many, and how long did you run them for?
Disclaimer: Anything posted by me is opinion unless otherwise specifically stated
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