[Swift-Rider]

So I have a 2007 CRF 250 thats bored out to a 270 that I bought not to long ago that was blown up. I am now just getting to the carburetor and wanted to know what kind of stuff I would have do/check for to see if it has the right jets... ect. Im not to sure if I would have to change the jet sizes since its bored out to a 270 or not.

Your help would be much appreciated.

[JimDirt]

Welcome to the site !!

I am surprised no one has replied by now .........

The best I can offer is the jetting specs from the Service Manual (specs are listed from 04-09) ... that should get you close enough and you should be able to dial it in with the fuel screw adjustment , if the fuel screw settings do not get it where it needs to run correctly , it will tell you by how many turns it has over or under the min/max , as to what way you need to go with jetting (richer or leaner)

Hope that helps

[Leardriver]

Start with the recommended jetting for a stock bore.
It sounds backwards, but most big bore kits take a smaller main jet. The increased vacuum and carb signal from a bigger air pump (engine) moves more fuel through the same jet.

[Swift-Rider]

Start with the recommended jetting for a stock bore.
It sounds backwards, but most big bore kits take a smaller main jet. The increased vacuum and carb signal from a bigger air pump (engine) moves more fuel through the same jet.

So do I keep all the other jets the same and just experiment with the main jet?

[JimDirt]

Go by what is on the charts above that I posted and you will be good .... Jets , needle clip position , fuel screw setting , everything you need is posted above , do ALL of it to those specs ...