270 Big Bore - Question abt Cam swap.

Hello Everyone.   I searched the message boards and couldn't find an answer so I thought I'd start a new thread.


I just picked up a 2001 Wr250f.  Before I even got to ride it I snapped the kick start lever in half...whoops.  So I've decided to tear the bike down and do all of the free mods, if they haven't been done already.  There is already excellent information out there on all of that, so here is my question.  My 250f has the 270cc Big Bore conversion.  I don't have any more specific info other than that.  Are there any considerations I need to make when doing the free mods because the bike has been bored out?  Specifically, can I still just install a standard '03+ Yz250f decompression cam?  Basically, is there anything that I need to do differently because it's bored out, or is there anything that for sure had already been done to the bike because it's been bored out?   Thanks for the insight guys!  The more I read on these threads, the more confident I am that the wr250f is going to be a great bike for me.




Yes, an '03 cam will bolt right in and help in lessening the starting "drill". Do you know which cam you want? The YZ cam will provide quite a bit more power than the WR cam. If the previous owner hasn't rotated your stock cam to YZ spec's, you can, and will notice the power increase. Do you know what jetting you are running? That's about the only thing that needs to be changed when running a big bore. Good luck, and welcome!!!

Maniac998 is correct.

I agree with maniac.

To get the most out of your BB, you're going to need to rejet. Do some searching, but the the short answer is you'll need to lean the jetting out.

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