Jetting specs

I have a 98 yz400f

stock motor &carb w/a white bros

header & pipe i live pretty much

@ sea level

i was wondering what jets,needle

clip position ect.

that i should run in my carb.

any input is greatly appreciated.



I run the White Bros tapered header and E-Series w/12 discs. My bike is a WR but, has been changed to YZ timing.

Read my signature below for the jetting.

OOPS....Use clip position #4 (from the top)



99 WR400f, YZ timed, MX-Tech suspension, Scotts steering damper, White Bros E-Series (12 discs), tapered header and a/f. Kouba T-handle for the fuel screw. Works Connection billet throttle tube and frame guards. Cycra Pro-Bend, triple clamp mount handguards. Thumper Racing rad guards, Renthal Jimmy Button highs, YZ Tank and IMS seat, YZ number plate, odo removed, EKP, 48PJ, 175MJ at 500-1000' Thanks James Dean!

[This message has been edited by Bill (edited 07-01-2001).]

'99 YZ-400 ( 420 kit ) E-series with 12 discs, 185 main, 50 pilot, 100 pilot air, 2 turns out screw, 4 th clip on stock needle.

( will try James Dean / Bill jetting sometime soon with other than stock needle. Supposedly gives two-stroke like hit! )

If you are running stock pipe you may need to jet slightly leaner than with our high output aftermarket pipes. They clean out gases better and create a leaner condition if not jetted accordingly. So for stock exhaut I would suggest 180 main, 50 pilot, 4th clip, 1 3/4 turns out.

Take care.


what kind of altitude

are you riding at?

i know that has a huge affect on carburation

right now i have 45 pilot 175 main

stock needle 3rd clip position from the top

but i am running a white bros e pipe

w/tapered header opened end cap.

0-1500' East coast ( Montreal area, Laurentian foothills ). The e-series will lean out your bike as you add plates. Check your plug colour but please do not forget to blow air through the hole provided in the casting before unscrewing. Go to the Stroker web site, they hace jetting specs there for the 98/99 and 00 bikes. Apparently the 98/99 came from factory too lean.

what is the web adress for the stroker web site?


did you adjust your tps

and cut the throttle stop

like they suggested on

the stroker website?

if so what bennifit did you get

from it?

I left everything else stock. If you have a WR you should look into the throttle stop mod. I don't think the YZ needs that mod.

Look up James Dean's posts on the WR side. They are using a different needle. Also look at Bill the Moderator's trailer when he posts. He has the needle model and MJ that he is using there.

I will try this combo later in summer.

Take care!

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