250-500cc Power valves size

I assume if I was wanting to go to 250 cylinder from a 300 - Id need new - longer power valves. Correct?

Why would you want to go to a 250 cylinder from a 300?

Quicker response , more revvy , easier to ride on the pipe ?.
Not sure really but like 250 power curve

LoL...if an '00 250 cylinder fits the 300 l'd swap ya!!

It does. Bolts right up.


I went from a 300 to a 250, because I trashed the 300 jug, head, and PV. I picked up a slightly used 250 setup for a helluva deal, so I went with it. Thinking it may take some of the edge off and allow me to ride longer with less fatigue. It's definitely a different power characteristic. One I don't particularly care for. It reminds me of riding my ol' KTM 200 too much. Running it hard on the pipe most of the time. Fun in the open, not as much in the tight where lugging would keep the wheel spin in check.

my original question still remains though - do you need to use the 250 power valves? I assume so - if they are the same sort of design as 125 .

I bought a 250 cylinder off ebay cheap but no power valves - it was also pick up only so it may not be happening anyway

Rockdancer, looking at the parts catalogue for a 2010 WR250/300, the actual valves are different going by part numbers - by how much, maybe give Stefan a call at R&D Husky?

thanks a lot OMG - it looks like its shaped to bore so will need to be changed - or will not give as good down low response I guess

I guess you'll play with the power valve height, jetting to get you a better response possibly porting mods. If you want to 'rev' faster then you may have to lighten the flywheel but then you'll sacrifice some low down torque.

Dunno mate...if it was me, l'd look for a complete jug from a 250, unless you can track down powervalves from the states?

Yep, definitely need the right power valve for the cylinder. That's the main reason I went with the 250 I found. The main piece (#11) got a chunk taken out of it by a piece of the piston when it let go.

I'd look into maybe porting and a pipe and keep the 300. Just my $.02

Looks like I got the 250 cylinder and head and near new piston - it was cheap so its insurance really . May not fit it up.
The guy selling it got an Eric Gore 265 kit for his -

While we are talking about it - Anyone have any 250 power valves and booster valve theyd sell ?

Thanks guys