James Dean Carb Kit Installed ~ I Need A Little Fine Tuning

Just installed the kit this weekend. Alt 5,000ft, 90 deg., 03 WR450, GYTR muffler insert, opened up the airbox, grey wire cut, YZ throttle stop. Previous problems:

- kick started ok, would not elec start for beans

- lots of popping on decel

- stall off idle in neutral (not a big deal, just not right)

Installed the blue #3 and 168 main. all other setting stock.

Took it for a short ride, runs hard, all problems disappeared. starts nicely with electric start.



How will changing from the stock air filter to a twin air filter and adding a power now affect my jetting if I am already where I need to be? I'll be installing these items this week. Thanks

Power Now and Twin Air Filter arrived and I'll be installing these this weekend. Much has been written about the off idle bog. On page 4-19 of the service manual under accelerator pump timing adjustment it describes the proper throttle valve height adjustment. The slightest fraction of an carburetor adjustment makes a difference, sometimes a huge difference. Has anyone made this adjustment to exact specifications (3.1mm or 0.122in) other than just screwing the adjustment screw blind?

This might also be a good time to bring up to those just now rejetting to pay attention to the alignment of carburetor joint and the cylinder head projection. It's real easy to get these out of alignment and the carburetor would be mounted slightly tilted which might cause an entirely inaccurate jetting evaluation.

The power-now will richen it slightly near 1/2 throttle. It should not need adjustment, but maybe a leaner clip position. The air filter will flow better on top-end and might use a bigger main jet, depending on whether you were already lean or rich.

It's best to make 1 change at a time to keep track of what is making the change.

Your are exactly right about the adapter flange off the cylinder head. The carb port is off-center and will misalign with the cylinder head if the rubber adapter is rotated off the alignment notches.



Sorry for the delayed response. Yes, you can simply move to a leaner clip position to clean the jetting up in the 1/8-1/2 throttle range.



bump :D :devil:I'm back :)

Hey Basic Blues,

I run the power now and twin air filter with the same air box mod as you. The red needle in position #4 should be right I am slightly rich at position #5. 160 Main rocks! Carb needs to be level visually only. Dont worry about it to the Nth degree. I adjust my screw 1/8th turn at a time while riding it up and down the street with the side cover off the carb. Just remember where you started. :)

Well i had some time today so i raised the red needle to #6 and changed to a 40PJ 13/4 turn on fuel screw. The flat spot is pretty much gone.It has very good throttle response in all the gears.Third gear wheelies no problem,not bad considering i'm 245lbs.I can't say it is a rocket but it realy does'nt have a flat spot any more.The biggest differance is it does'nt fall on it's face in third any more when you go full off then full on. :)

Try a 160 main. That will bring out the rocket in your bike! :)


Yes, try a smaller main jet, maybe the #165, before a #160. It sounds like you're close to having a good setting for your conditions.


I am in a little different situation.

9-11k rock crawling (i.e., Rubicon trail)using the same JD jet kit with the blue neddle and 4th position, 1 3/4. I am stalling profusely and am feathering the clutch continuously. I have tried a bigger PJ, moving the screw position with no avail. Are these guys just not designed to chug over rocks? ANY ideas would be appreciated. All other power bands are GREAT!

You need to be on the red needle in #4 at that altitude! Pilot should be OK stock with only one turn out on the fuel screw. 160 main jet

Hey all,

I'll be testing the recommended jetting specs which say to run a 170mj with the blue needle. I'm running a stock needle now and a 162mj and it seems perfect on top. There's no elevation factor to speak of but I am running an FMF powercore 4 and a Powerbomb header. I think the header requires a leaner mixture for mj. Anyone have a suggestion? Does the blue needle enable you to run a richer main than would have been possible stock? Should I test the 162 mj or would it be better to go right to the recommended 170mj?

As I suspected, the 170 was way rich. With the blue needle in cracking it WOT would bog,bog,bog. I had a 162mj in it before i installed the JD kit, and on top it ran well. Well, i worked my way down to a 160mj! This is in Michigan 600-800 ft altitude but it is about 80 degrees and real humid, which may require the red needle to get rid of the roughness at 1/3 throttle. The only thing i can think of that would make it different from the recommended specs is the darn Powerbomb header which seems to require much leaner jetting. Anyone else experienced this?

For those running my mods (see signature), here are my specs with the JD jetting kit. I'm running the Red needle with the clip in the 4th position from top. Big improvement over the Blue needle which was far too rich. I'm running a 162mj which actually DID NOT come with the kit. The kit provides 160,165,168,170 for main jets. Luckily i already had the 162. I have the fuel or pilot screw at 1 3/4 out, with no popping on decel. These specs work well for me in Michigan.

I just ordered a James Dean Jet Kit for my 2002 WR 426

I have the following:

*White Borther E Series header muffler assy

*YZ Cam timing

*Gray Wire Mod

*Air Box Lid off

*Aftermarket Airfilter

I had an '01 stock WR 426 before this and it was easy to start. This one is next to imposible to start. It fouls plugs left and right and is always a pain in the perverbial a**. I headed down to Terlingua, TX next week and would really appreciate some help. I am not the birghtest mechanic on the block, but I am willing to try anything to get this bike to start better. Once running this thing is an animal.

Environment is Houston, TX

*Seal Level

*Usually hotter ambient temp than the sun

*relative humidity straight out of the sauna

Any help would be greatly appreciated

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