WB's E-series Disc Tuning

Does the greater nuber of discs that you use with the e-series result in the bike running leaner? I decreased my number of discs from 9 to 5, cranked up my bike, rode it about 300 yards, and fouled a plug. How many discs are you (3rd and 4th gear primarily) 'trail weenies' using for elevation around 500 to 1000 feet?

Another thing, my bike did have a hesitation problem when giving it a quick throttle running 9 discs. When I moved down to 4, the hesitation stopped.

Cannot type tonight - second reply should read 5 not 4.

I currently run a s-bend e-series and yes the number of discs will affect jetting...how drastically I am not sure. I randomly picked 10 discs and was very impressed with the seamless power as well as a very nice tan color to my plug (checked it at the conclusion of a long enduro). This friday I plan on experimenting with 12 discs and maybe even checking it with 5 just to determine trade-offs with various numbers of discs. The only down-side to this silencer W/10 discs is the noise. :)


2000 Yamaha WR400F

1988 Honda NT650 Hawk

1977 Suzuki RM250B

1974 Honda XR75K1

I have the bike configuration that is shown in my siganture. I run 12 discs (very loud). When I first put the pipe on I was using 12 discs and then checked the plug with the stock jetting it looked lean. So I removed 3 discs and almost immediatly fouled a plug. I can tell you the number of discs do affect the air fuel mixture, power curve and decibel (sp?) output.

I ride sea level - 1000'. Tight woods and MX. This is what I run for jetting in my 99:

MJ-175 and going to 178


Needle-stock in #4 clip position

Fuel screw-2.0 turns out

Runs great but plug is still a little lean.

Good luck



86TT225, 98CR80, 99WR, WR timing, throttle stop trimmed, air box lid removed, White Bros head pipe, silencer and air filter. Odometer and headlight removed. Moose hand and mud guards.

For the record I'm running at 1000 feet and have the throttle stop shortened, airbox lid removed and E-series w/10 discs. Most of my riding is woods and MX. My jetting is: -175 main

-45 PJ

-stock needle set at the fourth groove from top and have not touched the fuel-screw.

I'm very pleased with my jetting for this set-up at 65 degrees F...after hearing of how a few discs can change jetting dramatically I may stay with 10 discs except in extremely hot or cold conditions where I will probably vary by no more than 1 or 2 discs to compensate for temp changes.

Moto-Mike: please post your comments after your ride Friday. Would definitely like to know the results of adding/subtracting discs.

Well I went riding today...For about the first half of the ride I rode with 10 discs and then switched to no discs. I decided to try this after seeing the latest issue of Cycle News where they featured Randy Hawkins YZ426F. It said he uses the E-series on his enduro bike and the picture that was shown of his bike had no discs just the endcap! Well my seat of the pants impression was that no discs was as good if not better than 10 discs. I have not had a chance to check the plug but there was no popping or hesitation of any kind. My friends (JLM400) YZ400 has a straight thru exhaust as well as most of the silencers I've seen for closed course riding. If a spark arrestor is required where you ride then run the discs if not go with out! Both set-ups felt very close. Power output is very subjective (they were that close)...either way you can't go wrong.

I would also be very interested in hearing these results. I'm about to make the big jump to YZ timing and putting on my White Brothers E-Series exhaust. I'm struggling with how many disks to put on. It sounds like 10 to 12 is best for performance but very loud. I want to ride in some of the enduros, grand prixs, and hare scrambles here in Southern California and I am concerned that with that many disks I may not pass tech. Taking disks out at short notice doesn't sound hard but it sounds like a jetting change would be needed and a performance would decline. I'll probably go with 10 disks and see what happens.



2000 WR

Moto Mike They say that running no discs actually reduces power on the dyno test. http://www.whitebros.com/offman/YZ400WR400F.pdf Yes, I know the dyno room and the real world are very different somtimes but it is a place to start from. Becareful not to lean out on the top end with no discs installed.

I run 12 discs, 48 pilot, 180 main, screw at 2.0 turns, and a DVR needle at the 4th position and I will replace the DVR with DTM needle Monday. I'm still a little lean off idle. The needle change was Clark's suggestion. (Thanks again Clark :) ) I'll let you guys know how it turns out.


00'WR400 75'Yamaha 250 enduro

White e-Series S-bend 12 discs, Yz timed, rejetted to Clark specs, throttle stop cut, lid removed, Topar Racing top clamp, Tag Metals T2 bars, Scotts damper, Devol disc guard and frame guards, lights removed, Cr routed Fastline brakeline, Acerbis Rally pro hand guards fastened to the top clamp, Gel grips Live in Southwest Ohio

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