Sorry but were both right I pulled those numbers right out of the service man. There are two different #'s for the old 250 the one you stayed and the one I did.

 

So in theory the cdi box to run is the old klx250r if you have 250cc displacement, but if you are going to run big bore is it more benifical to run the klx300r cdi or the old 250r?

 

Its not as simple as that. I'm trying to move the powerband up with cam selection with my stock cams it got plenty of toque but I'm looking for a little more on top. The cdi from those bikes aren't just plug and play.

 

I know that they aren't plug and play, I am not sure if I am going to bigbore or not and if I am going to take the time to get one figured out I want to use the right one. I am not that smart when it comes to timing advance and all that stuff so I was wondering what one would be better for the bigbore the old 250r or the 300r, so if one comes up cheap I would get it.

 

Both the 250R and 300R required the wiring modification, so if you're going big bore you might as well get the one that is better suited to the larger displacement (300R). That said, you will feel a world of difference going large borewithout changing the CDI at all. I guess it all depends upon how much you live in the upper RPM ranges.I have ridden bikes with the 300RCDI installed and seat of the pants tellsme you get bit better response and it's somewhat more free reving. You won't see much more than about a .5hp gain on the dyno, but you will feel the difference...that's without adding an aftermarketcam.The right cam combined with theCDI would result in them complementing one another. I know which cam I'm getting, but that will have to wait until next season.

 

One other thing these boxs have no rev limiters where ours does.

 

Can you provide some more info on getting the 300R CDI to work. I have a 300R CDI that I've played with a few times but I just couldn't get it to work.