James Dean Jetting Kit Now Available For WR400/426/450

Guys & Gals,

If you are deliberating on buying this kit, all I can say is DO IT. I've had an 02 WR426 for about a year now and hadn't touched jetting or engine (scared of stuffing it up completely:) and I thaught it was fine, UNTIL... I ordered kit. Kit arrived in a week (Australia) and followed the easy to understand instructions to the letter and fitted in an hour. Rode the bike today 22 Deg C. I couldn't believe I was riding the same bike. My bike has turned into a 450, its super smooth, yet so responsive, it's hard to explain how good the bike felt. Even the exhaust note has changed into a raspy sound like a 2 stroke without huge powerband. All I can say is I hope James reads this cause he has one very satisfied customer.

Thank you James you have obviously spent hours and hours on wr's to get us a bolt in kit that is just fantastic from the word go.

Very Happy

Kev :)

The purpose of this note is to share my JD jet kit/ Power Now experience. I live in Michigan, and have trail ridden my 2004 WR450 twice with JD jet kit components, and a Power Now carb. insert. I have done all the modifications to get a WR450 to run correctly (GYT-R insert, cut gray wire, YZ throttle stop, and air box mods). The temperature was 60 - 70 for both rides. The first ride was with the "Blue" needle (clip in #3), 168 main jet, 45 pilot jet, and 2 turns on the air screw. The second ride was with the "Red" needle (clip in #4), 170 main jet, 45 pilot jet, and 2 turns on the air screw.

Observations from the first ride: Some pre ignition during full throttle. Sputtering during 30-50 MPH cruise. Throttle response like a two stroke. Fuel economy was 25 MPG.

Observations from the second ride: No pre ignition during full throttle. Full throttle power seemed higher than on the first ride. No sputtering during 30-50 MPH cruise. Throttle response like a two stroke. Fuel economy was 32 MPG.

PS- I wish all companies had Customer Support like James Dean. James promptly solved my concerns via e-mails and phone calls. I love my WR450. The sound of a 13,000 RPM thumper is a wonderful thing! I am curious about one thing. If KTM can sell the 450EXC ready to race, why can't Yamaha sell the WR450 ready to race? Cutting the gray wire was a little scary.


I have a 07 WR450F with our kit in it and not many miles on it. i have gone from a red neddle #4 to #5 clip position 165 to a 170 main, #45 pilot to a #48 and still have some decel poping. it seem to be getting better, but i'm conderned that i might be going in the wrong direction.

i've done all of free mod's,air box, pluged AIS, GYTR slip on, K&N air filter,gray wire. I'd like to start with sea level spec's and adjust from there. what do you recomend? Thanks 42A

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