YZ426 Jetting Boosts YZ/WR400 Midrange Power

41 replies to this topic
  • James_Dean

Posted July 06, 2000 - 04:35 PM


If you want more power, here is an easy way to get it-
or - #5JG-14916-EN (OBEKN)-slightly richer
or - #5JG-14916-ER (OBEKR)-slightly leaner (stock YZ426)
The reason why is:
-The carb needles on YZ and WR400's have very little taper. The tip of the needle at full throttle restricts fuel flow nearly as much or more than the main jet. This makes for a lean mixture between 3/8 and 3/4 throttle.
-For 2000 Yamaha corrected this lean spot on the 426 with a steeper taper needle. It gives a boost in power between 3/8 and 3/4 throttle. Where the 400's jetting is smooth under a roll-on, the 426 jetting pulls harder and takes less throttle to get the same acceleration.
-The parts department records will say that the needle 5JG-14916-EP is EVP, it is not! It will come as an EKP. (same for EN and ER) The taper on the EK- starts at nearly the same distance from the clip as your stock DVR,DTM,DRS,D...
-My suggestion for a STARTING point is to use clip #3. (This is the same as EMN#4)
-PLEASE NOTE: Only YOU can jet your bike for your conditions and style. If you post questions I will try to help get the most out of it for you. The most likely needle to work for most riders is EKP or EKN.
-To make this assessment I have collected 10 needles with a mix of 5 straight diameters and 3 tapers. Most were run at more than 1 clip position to find the boundaries of rich and lean throttle response. The main jet was pulled out for part of the testing to verify the needle was not restricting full throttle(20 miles worth,didn't foul out). Also, 4 pilot jets were sorted through. The carb has been off at about 20 times(glad it's a 2000WR). It was run with both stock WR cam timing and YZ timing. It was also run with both stock muffler and '99YZ muffler. It was then compared back to back with a stock '99YZ and '99WR w/FMF PC IV-2.
-You will probably want use a richer pilot jet, #45-#48.
-The main jet will should be in the range of #162 to #172. The needle will allow the main to flow more, and the YZ426 went to a #165 main where the YZ400 had a #175.
There are a family of needle options with slightly differing straight diameters. The straight diameter affects the transition from idle, between 0 and 1/8 throttle. Here is a list from lean to rich, the midrange will be identical:
5JG-14916-ER (OBEKR)
5JG-14916-E1 (OBEKQ)
5JG-14916-EP (OBEKP)
5JG-14916-EN (OBEKN)
Sudco needles are also available as EMN, EMP, and EMR which are just 1 clip leaner. They are brass and cost less. 1-800-998-3529

The 3 letter needle decoding is as follows:

FIRST LETTER is taper :
D=.75 degrees
E=1.0 degrees
F=1.25 degrees

SECOND LETTER is clip height from mid-taper(2.515mm diam):
D-- needles R,T,V have tapers starting close to the E-- with K or M as a second letter. This letter and the clip position get the taper to transition at the preferred throttle position. This is for jetting 1/4 to 3/4 throttle:

DR- is one clip richer than DT-
DT- is one clip richer than DV-
EK- is one clip richer than EM-

THIRD LETTER is straight diameter: M,N,P,Q,R,S from rich to lean at 0-1/4 throttle:

The codes allow fuel mixture changes at specific throttle positions. It's best to graph them as diameter vs. throttle position to identify changes before switching needles. Comparing all the stock needles used, DVP and EKP fall right in the middle. :)

Have Fun Roosting!!

James Dean

[This message has been edited by James Dean (edited 10-03-2000).]

  • RodH

Posted July 06, 2000 - 05:46 PM


Since you tested it on a 2000 WR400, am I right in assuming that the only the YZ426 had the steeper taper needle changed ? And that the 2000 WR is affected just as the 98-99 YZ/WR's ?

Thanks for the info, I think that will be my next step in search of more power :)

RodH Canberra, Australia<A HREF="http://www.400thumpers.oz-au.com" TARGET=_blank>
400 Thumpers Australia</A>
2000 WR400F See Photo's and Modifications

  • Grum_from_Oz

Posted July 06, 2000 - 05:57 PM


Hey JD,
thanks for the jetting tip about this particular needle. I rang my dealer today and he says there is no such thing as an EP needle just EVP. I was prepared for their negative answer on the EP needle but when I queeried them about the EKP needle they said the only needle available is an EVP. Is the EVP the same as an EKP? Is the EKP the equivalent to an Aussie EVP?
Sorry to shed confusion onto a topic made most clear by your previous post.
I just want to be certain before I shell out $40 for a part that may or may not be the right one.

Many thanks Grum from Oz. :)

  • James_Dean

Posted July 06, 2000 - 07:39 PM


-The parts dept. does not show the data correctly. Make sure that they order the 5JG-14916-EP and they will tell you you are ordering an EVP until it comes, then look and see that it is in fact EKP. It happened to me that way. This is listed in the YZ426 shop manual as EKP correctly.
-The 2000WR has the flat taper also - DRS(USA) or DRQ(EURO)
James Dean

  • Brad

Posted July 06, 2000 - 08:31 PM


Damn Grum,

You're paying $40 for a needle? You should send me your adress and I can get one here, put it in an envelope and mail it to you. With the current exchage rate, a needle here is going for about $17 (AUD) or $10 US. I'm sure mailing one in an envelope couldn't cost more than a buck or two.


  • Taffy

Posted July 06, 2000 - 10:04 PM


excellent work James. it's clear that you have worked very hard on this, your pet project. to share your info is great your a real amatuer!!!

i'm lucky enough to understand what you're saying & for others it will be a case of look mate, so what are you saying (finally)?

how about the carb people being told you want some proper graphs to post. how about you being given your carb bits for free from someone. mindful that they will be getting lots of extra business.

Jesus Bryan, you've got 430 registered members & if i'm an example, i know a YZ & 3 more WR owners who hang on for all the info i can glean!

your last mail if shown to a shop would convince anyone that you are very analytical in your work. they should also offer you their best advice (saved for the top boys)

P.S. don't ask anyone who doesn't race though.

  • James_Dean

Posted July 07, 2000 - 06:18 AM


--"A man's always gotsta have an edge", if I raced with you guys you never would have gotten this from me. :)

[This message has been edited by James Dean (edited 07-07-2000).]

  • Vincent

Posted July 07, 2000 - 08:25 AM


James, am I correct in assuming this will only apply to 2000 model WR's? They have a different series carb on them right? The jetting specs will be different then too on our 98/99's. What is the consensus on the best needle for or 99 WR carbs? Still the DVP?

  • James_Dean

Posted July 07, 2000 - 11:40 AM


I would anticipate that this will apply to both carbs from 98/99 models(FCR) and 2000 models(FCR2). The carbs are using the same internal components and nearly the same jets. The stock 2000WR carb needle (DRS#3)is in nearly the same relative clip position as a '99WR (DTM#4)with the same taper. The EKP needle suggested is half way between a stock '99WR and '99YZ(DVR) on the low end. Hopefully this will bridge the span of whatever pilot jet you are currently using. The first time I noticed the power lag was while riding '99WR not a '00WR.

[This message has been edited by James Dean (edited 07-07-2000).]

  • Guest_Guest_*

Posted July 10, 2000 - 05:04 AM


Is The 426 needle: 5JG-14916-EP-00 the same as the neddle listed for the YZ400: 5BE-14916-EP-00.
As the YZ400 needle is cheeper i was wondering why and if it had anything to do with the change in carb.

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  • James_Dean

Posted July 10, 2000 - 06:14 AM


No, they are not the same. Do not get the 5BE version. The taper starts too far down on the needle. Yamaha was mistaken to have put this as an optional needle.

  • jj

Posted July 10, 2000 - 07:23 AM


James, I've been hesitant to do any jetting because my bike has run almost perfectly in stock form. So far the only thing I need to do is clean my accelerator pump.
By the sounds of it I could be missing some power by not jetting my bike. You and I ride in the same areas so I was wondering what set up you would suggest for me if I were to do some experimenting. I ride a 99WR, wr timing, no air box cover, stock exhaust (with and w/o baffle).

Hey how did you seat and tank turn out?

Thanks in advance!

JJ - 99 WR; WR timed, stock jetting, Scotts stabalizer, Scotts triple clamps, Pro-Tapers, Terry Cable Hot start, MSR Raptor clutch lever, Moose skid plate, Works frame guards, Acerbis Pro Rally guards, Renthal MD-soft grips, Russel speed bleeders, Factory Effect graphics, YZ rear fender

  • James_Dean

Posted July 10, 2000 - 03:31 PM


JJ and others,
If you have a '99WR and are interested, I will have the EKN in a '99WR this weekend. The needle position will be set at #3 for a first attempt. Otherwise it will be stock jetting - #45 pilot, #75 air jet, 2 1/4 turns on pilot screw, and #168 main. (he gets the EKN because I wanted to use the EKP) Also might have a '99YZ with EKQ. (same story)
- Will try out the Clark tank and YZ seat this weekend if I get it as promised.
James Dean

(P.S.-If anybody E-mailed me last Thursday or Friday, it got lost accidently. Please resend it if you please)

  • James_Dean

Posted July 17, 2000 - 03:44 PM


UPDATE:The '99WR ran perfectly with the EKN needle for my riding partner. (It is only slightly richer than EKP from 0-1/8 throttle.) He could feel the pull at 1/2 throttle on gravel roads and uphills. Less throttle needed to get more pull. Down at idle and off idle no difference was felt at all. Went 90 miles on 3 gallons gas, so its not any less fuel efficient. He's happy and wants me to find some more power... His words were- "hard to believe that little part could make such a difference, more than my FMF silencer did"
-FMF PCIV2 airbox lid on/no snorkel
-Jetting shown above

[This message has been edited by James Dean (edited 07-17-2000).]

  • Kris_Stratton

Posted July 21, 2000 - 05:50 AM


I tried to order an EKP but it is backordered. I am picking up the EKQ today. I have a 99 YZ 400.

I am running at 500 to 1000ft.
Crurrent jetting is:
Stock Needle - 3rd Clip,
Fuel Screw at 1.5 turns.

With the new needle I understand that I should go down on the MJ. How much??
I have a 170 and 175 to try. Should I pick up anything smaller or inbetween. Not sure where to start.
I will let you guys know how it works after this weekend.

Thanks James.

  • James_Dean

Posted July 21, 2000 - 11:03 AM


#170 main and 3rd clip from the top is a good starting point. Keep the pilot and fuel screw unchanged.

  • James_Dean

Posted August 04, 2000 - 12:58 PM


:) :D :D

[This message has been edited by James Dean (edited 10-03-2000).]

  • James_Dean

Posted October 03, 2000 - 10:49 AM


-Back to the top for those who are new or missed it...

I received some feedback from a '99 YZ400 owner last weekend that was using an EKQ needle in his carb. He thought it increased the torque at 1/2 throttle and made it more like his old XR600 and CR500. He was using a #162 main but wanted to try a 168 or 170 next.

My current jetting in my '00WR400 is:

pilot #48
pilot screw 1 turn
pilot air jet #100
EMN #4 clip (**)
main #170

60deg F, 500-3500ft elev.

YZ cam timing, YZ muffler, no airbox cover, cut throttle stop

(**)-The EMN needle has a small modification, rounding the taper start.

James Dean

  • mcarp

Posted October 03, 2000 - 04:01 PM


JD- I have a similar setup bike ('00 YZ timed, YZ pipe etc. I am running 48PJ, stock Air jet, 175MJ, DRS #3. I just changed the timing so I am starting fresh again with new jet settings after having the jetting perfect for WR timing. Right now it seems to run great, but I am always looking to improve performance

Curious why you chose the #100 air jet. Where you too rich with the stock air jet?

Are you still very much convinced the stock YZ426 needle is the way to go?


  • Speeder

Posted October 03, 2000 - 04:29 PM


I have a 2000 WR, WR timing, no airbox cover, Up-Tite Racing (George Erl) wide open LOUD pipe... CA Desert riding.
I think James is right about the EKP working well with wide open exhausts, as the EKP#3 with a 180 Main made a huge difference in my bike. (I know the 180 is a bit larger than most people run, but the bike fell flat at top without it). I also want to try the DVP.
Thanks to James and Clark for the tons of information.


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