99 jetting tips

2 replies to this topic
  • mat

Posted October 02, 2001 - 04:10 PM


anyone know a good ballpark for jetting on a 99yz400, it has a e-series pipe and white bros air filter, found the exhaust leak i posted previously about but it still backfires some but not as bad as it used too thanks

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  • Boit

Posted October 04, 2001 - 06:11 PM


It may not apply to you but I ran into this problem early on with my 426 and it drove me up the wall. What I discovered was that the adapter that the air box boot slips onto at the carb has two Allen head bolts holding it onto the carb. If you look closely, you will see that the heads of these bolts ONLY contact the pressed-in bushing of the adapter. One of the bushings on my adpater lost its integrity and the adapter actually began to slide over the Allen head bolt creating a small gap and resulting air leak. I found it as I was slipping the air boot back onto the adpater and noticed that the adapter suddenly moved and I could visually see the gap. The easy fix is to install a washer under the Allen head bolt that overlaps the bushing onto the adpater tang. Even if your bushings are still tight, it's good insurance against this type of problem in the future. One less problem to worry about is one less problem to worry about.

  • Bill

Posted October 05, 2001 - 02:26 PM



Try the jetting in my profile. It is a tested and trystworthy configuration, thanks to lot's of work by James Dean.

I YZ timed and install the below jetting at the same time. The bike starts first or second kick, any and everytime. It also runs stronger than ever. Through the entire rev range.

Also note my elevation.


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, de-octopussed (Thanks Clark) EKP #4, 50PJ, 175MJ, 100PAJ and 65 SJ at 500-1000' Thanks James Dean!

[This message has been edited by Bill (edited October 05, 2001).]

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