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

42 replies to this topic
  • Steve_Claus

Posted July 02, 2003 - 11:41 AM


Check them out:

Jetting Products from James Dean


  • BlueThunder

Posted July 02, 2003 - 01:25 PM


JD..can I will call the kit? Just up in Federal Way so it seems a shame to ship it. Promise I won't hit you with the 20 Q's on jetting..... :). Got an uncle who's a very renowned doctor and he gets the medical questions by everyone he comes in contact with. Very annoying to say the least.

  • ddialogue

Posted July 02, 2003 - 04:15 PM


Who can I talk with about this kit? I would like to know how JD's recommendations will change when using a muffler insert (specifically, the PMB insert.)

  • Indy_WR450

Posted July 02, 2003 - 04:48 PM


JD cruises this forum and he will help us with his kits. I just got my confirmed UPS shipment tracking number. I should have it next week! :)

  • The_Blue_One

Posted July 02, 2003 - 05:11 PM



I used the uncorked instructions for my 450.It was spot on for my area and the bike fired right up and ran great.I am running the baja baffle right now ,but just ordered the pro circuit 496 pipe.

You can pm James_Dean and he responds quickly.

  • Steve_Claus

Posted July 02, 2003 - 06:15 PM


I just got my confirmed UPS shipment tracking number. I should have it next week! :)

Its actually a US Postal Service (USPS) delivery confirmation number. We ship these priority mail (2-3 day delivery including Saturdays.) You should receive the kit on Saturday, Monday at the latest.


  • James_Dean

Posted July 02, 2003 - 07:52 PM


ddialogue and others,

The kit has a very good standard setting to start from. This setup will work in most WR's and YZF's with no need to change any other jets in the carb and take a big jump in performance. Modifying the exhaust and cam timing will work well with the standard setting, and better with fine tuning. Use the same instructions to start with.

The intent here is to give you a jetting kit that I would want myself.
---If a rider wants to make the installation and just go ride, it's a simple change with all the parts and instructions for a wide range of conditions.
---If a rider wants to maximize performance, the 2 needles and the range of main jets will give the most gains you will find on a modified bike with some careful test runs.

I have all the needles from tapers Cxx, Dxx, Exx, and Fxx to diameters xxL, M, N, P, Q, R, S, T, and NCVN, NCVP, and NCVQ. All these needles were run at different times and compared before launching into the design of the kit's triple taper needles. Each throttle range from 0-1/4-1/2-3/4-full was tested over and over to decide what diameters and tapers would give the best performance. It wasn't made by focusing on any single condition. The jetting comes from riding for weeks and keeping notes on every test and a wide range of conditions. It's been tested from sea level to 12700ft and dyno tested on the KTM 400 to confirm the needle effects on full throttle.

If you have ever read the "Jetting Q's", there are so many aspects that go into developing high performance jetting that it takes careful evaluation. Taffy has some great suggestions on pilot air jets and needle design. The kit does not suggest changing any pilot jets or pilot air jets. The stock pilot jets are recommended with the kit. Most riders want a quick and simple correction so they can go ride with a performance gain and minimum amount of work. Yamaha developed the low speed jets to work together and I'm going to defer to their settings in most cases. The richer kit needle will offset lean conditions in the same way an EMM or EMN needle will. The Leaner needle in the kit will also match idle and off-idle response with --P and --Q stock setings.

I know this is too much technical detail for most riders. :D The bottom line is the jetting kits are designed to make a quick and inexpensive performance gain with potential for more than any stock parts can deliver. :)


  • beezer

Posted July 05, 2003 - 02:16 AM


All I want to do is throw in some brass and go riding.

I'm goning to order a kit Monday.

  • HollandWR426

Posted July 16, 2003 - 09:29 AM


Question for JD and company,
OK, I just ordered the kit and already got the confirmation number :) I was wondering if you could give me the settings I will need to try when I get the kit. I know it comes with instructions, but I am not sure if they are based on a stock bike or if it includes various settings for different mods. My bike is an 02 WR426 with a Baja Designs Baffle, and airbox snorkle removed. I ride (dual sport, trails) in Michigan at about 500-1000ft. Temps around 80 (average). What would you suggest I throw in and set everything at once I get the kit? I don't want to keep changing things once in so your recommendations are appreciated.


  • James_Dean

Posted July 16, 2003 - 09:43 PM



I would suggest using the kit settings described with blue marked needle clip #4 and #168 main jet(for insert baffle), stock pilot jet. Adjust the fuel screw as needed for low speed jetting. You might want to use clip position #3 for extra mileage on the dual sport rides too.


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  • HollandWR426

Posted July 17, 2003 - 02:18 AM


Cool. Thanks for the advise. I'll see how she rides as soon as they come in. Hopefully by this weekend.


  • mjp426

Posted July 18, 2003 - 06:53 AM


HollandWR426, I hope your bike runs as well as mine after you put the kit in. My bike ran so different(better)on the bottom end that it took a while to get used to it. My bike is a gas to ride now. I was considering a 450 but I really don't need to fly quite that far into the bushes anymore. I have 3 friends with WR's that are going to buy kits because they like the power delivery on mine. James Dean, thanks for doing the testing on my bike. Lars says his YZ rocks.

  • James_Dean

Posted July 19, 2003 - 05:40 AM


I will be on Vacation 7/19-7/27

There are many other experienced riders to answer your jetting questions here.

Keep up the good discussions!

The 4-stroke FCR Jetting kits will still be available here thru the shopping cart, www.JDJetting.com


  • the426master

Posted July 20, 2003 - 01:40 PM


I have a jetting blurp, my bike will die when I barely crack the throttle it dies some times win I am rolling with my motor is brakeing and I give it gas it dies will this kit fix that

  • BlueThunder

Posted July 20, 2003 - 02:36 PM


Get the kit and do the BK mod and you should be good to go. :)

  • sodbustercb

Posted July 20, 2003 - 03:15 PM


I did the bk mod

  • BlueThunder

Posted July 20, 2003 - 03:44 PM


sod....426master was trying to get rid of the cough on initial throttle opening....the right pilot and the BK mod will fix this combined with JD's kit.

  • WR_Jason

Posted August 06, 2003 - 05:29 AM


It looks like there is one kit for the YZ/WRs, dose this mean I need to use YZ timing on my WR 400 to use the JD kit?

  • basicblues

Posted August 06, 2003 - 04:58 PM


YZ timing is not necessary to use the kit. Good Luck.

  • James_Dean

Posted August 06, 2003 - 09:41 PM


The kit works with both YZ and WR cam timing. I've tested the jetting both ways and results were great in each case.



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