JD, what's wrong with stock yz250fs

I'm thinking of getting the JD kit for my 2002 yz250f. I know that it's a different needle along with a larger main jet that cleans up the jetting and I have no doubt that it works after reading all the positive testimonials.

I'm just curious though, what is it about the stock jetting that is off, and what happens if you try to correct it just by adjusting the stock needle position.

What I'm asking is what rev range is the stock jetting to lean/rich, and how is adjusting the stock needle not an imperfect solution. Thanks :)

The stock needle has a single taper machined on it. The jetting kit uses 2 needles with 2 different diameters and 3 tapers machined on each to deliver fuel more precisely for the throttle position and conditions.

---To be more specific, the stock needle has lean and rich zones that can't be tuned out with the pilot, clip, and main jet without compromising elsewhere. The kit needles are designed to make an improved, even flow of power, and more response. More precise tuning and instructions for installation and setup help give good results with little effort.



Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now