First time carb work...

Well, I took the plunge and have attempted to work on my carb. I know this isn't a big deal for most of you, but try to remember back to first time you removed a carb, cleaned it, figured out jetting, etc... Big step for me. :D I just put my bike to bed for the night, washed my hands, and headed straight for the computer. I had to come make a few comments and ask a few questions...

I've read most of the archives related to jetting and carb work in general and it helped out quite a bit and gave me several things to look for. Thanks!

First of all, a few things to know about my bike: The bike starts typically on the first kick and only has an occasional pop on deceleration. I live in Denver and ride mostly at 5000 - 8000 feet elevation. Considering I had no idea, until tonight, how the bike was setup, I figured I may not be getting the performance I could if it was setup wrong..

In reviewing OEM jetting settings, I realized that the previous owner has made a few changes.

He is how he/she had it setup:

Main = 158 (no, not 168, I triple checked :D )

Needle Type = DTM

Needle Position = 4

Pilot = 45

Fuel screw turns out = I think 1 1/2

Stock exhaust pipe, but e-series slip on (is that the proper term) with 9 discs.

Now, why would he have put a 158 main??

I checked the spark plug to see how it looked. Get this, it is an NGK CR7E. Isn't is supposed to be a CR8E?

This is the first time I have had the plug out. I noticed a bit of water at the very bottom of the plug, but I had just given the bike a wash. I can't see that being a good thing though!? The bottom of the plug (where you set the gap) was black at the very base and through about 3 threads. I have no idea what this means. :D The rest of the plug looks brand new.

In checking my carb slide for the "dreaded crack", I found not only a crack, but this crack is almost a full circle. I take it that's bad. :) Looks like I'll be heading over to the bike shop tomorrow to pick up a new one.. Should I buy OEM or another brand?

My accelerator pump was filthy. The metal "cup" attached to the diaphram is all rusted too. I assume I should replace it?

I think that was all of my discoveries.

Any suggestions on jetting (if different than Bryan's setup in "Jetting Examples") or thoughts on the above findings would be GREATLY appreciated!

Thanks in advance.



99WR,WR timing,throttle stop removed,Uni filter,E-Series pipe,carbon air box,Pro Tapers,lights removed,YZ tank,13 tooth sprocket


the ngk 7 plug is'nt a problem, it's something i've been recommending for ages. if you don't do much long distance WOT this plug is possibly better than original.

it's equal to a lawnmower plug & will take all kinds of mixture abuse except for very hot for a long time.

would you send that slide to James Dean, i know that he wants to experiment with slide cutaway height.


TYhe water is from washing your bike. You need to plug the hole on the side of the cylinder prior to washing the bike. The jetting I can't help you with, I ru=ide at sea level. But you plug is rich, but unless you ride the bike, warmed-up at WOT in 4th or fifth and hit the kill switch at WOT, your reading the plug at low RPM or idle. I would also think about going back to the CR8 and get the bike jetting correct to match the stock plug heat range.

Just my .02 and yes, you can give me change!



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. YZ stock tank and IMS seat. Renthal Jimmy Button "highs" and Renthal Soft half waffle grips. AMA, SETRA.


No way I'm putting a cracked slide in my bike for any experiments.

The DTM#4 is a rich needle and location. The main and pilot/pilot screw appear to be set lean to compensate for it. There's a saying, "If it ain't broke, don't fix it".

If you want more performance, expect an adjustment period to get it just right. Clark has had good success with the DVP#4 (?) and I've been recommending the EKP#3 or in your case EKN#3.(search for EKP) Either way a bigger pilot #48 at about 1 turn. Main jet with EKN#3 will be around #162 at your altitude. DVP#4 will be bigger also, see the tech section tips.


Thanks for the insight fellas. What's WOT?

Would it be a safe bet to simply change jetting to match what the Colorado guys were using prior to the YZ timing change over?

I strongly agree with the point, if it aint broke, don't fix it, BUT I'm hoping that the change in jetting will improve power/snap, etc... If jetting won't do this, I just might leave well enough alone unless there's a reason to change things..


99WR,WR timing,throttle stop removed,Uni filter,E-Series pipe,carbon air box,Pro Tapers,lights removed,YZ tank,13 tooth sprocket


I imagine the previous owner rejetted leaner for altitude but was too lazy to take the carb off and only changed the main (I believe your needle, clip position, and pilot are stock for a 98-99 WR). Maybe he already had the 158 from some 250 or something in his tool box. That IS a pretty small main. You should try the jetting James recommends.

I installed a Russel in-line fuel filter (little anodized aluminum cylinder with solid element at any Pep Boys or hot rod store) to keep my accelerator pump clean. There are two o-rings/gaskets on the pump cover, one sits in an indention in the cover, the other in an indention in the carb (they are not the same). Make sure you didn’t drop one or both of these. If the rubber portion of your diaphragm is still pliant and in one piece it should work. On the other hand a new one is only $11. You can order the diaphragm, needle, and jets (and the o-rings :)) from Sudco (800-998-3529), I would be surprised if your dealer has the diaphragm or needles James recommends. If your diaphragm was rusty make sure the actuating rod that depresses the diaphragm is not sticking.

I used to try and read my plugs but I no longer think that is a good way to check jetting. How the bike runs is obviously more important. But if the electrode is rounded off replace it. The number on the plug is the heat range, with a 7 being one step hotter than an 8. Maybe the previous owner fouled his plug and thought he needed a hotter one. You are correct, the 8 is stock for a WR, 8 or 9 for my 426.

I think it is a good idea to do some work on your bike yourself. Knowing what makes it tick makes you a better rider, makes it harder for a mechanic to rip you off, and may someday prevent a long walk. Actually, since you have discovered a cracked slide it looks as if you may have already saved yourself a long walk, not to mention additional damage (and expense). Congratulations!

WOT = Wide Open Throttle

[This message has been edited by Hick (edited 10-12-2000).]

Hi Scott.

DTM #4 is way too rich for Colorado. The stock DTM is at #3 and most of us that ride high (with WR timing) leaned it out to #2. I think DTM #3 will work OK at Rampart/Woodland Park though.

The main at 158 is way too lean and not necessary. The dealers jet it this way because they don't understand AT ALL how the clip and pilot effects the engine. You can go to a 165 for sure and probably even higher since the main is only used at full throttle (James proved that beyond a shadow of a doubt).

The pilot of 45 seems to work in Colorado for most WR riders. However, I kept fouling plugs on long downhills at high altitude. I changed to a 42 pilot and the problem went away. Of course the dealer told me to decrease the main to fix this problem. Isn't THAT a laugh? So I'd stick with the 45 with WR timing unless you have similar fouling problems on long downhills.

Just my 25 cents worth.

Good luck,


Thanks Bryan,

Honestly, I plan on copying your WR setting posted in the technical section to start with. Also, I'll be putting the CR8E in replacement of the CR7E.

I guess my biggest question now is, what should I be looking for after I make all these changes? Quicker bike I hope. :)


99WR,WR timing,throttle stop removed,Uni filter,E-Series pipe,carbon air box,Pro Tapers,lights removed,YZ tank,13 tooth sprocket

The good news: I now have in my hands a 165 main, 168 main, and 42 pilot.

The BAD news: That cracked carb slide is gonna run me well over a hundred bucks to replace!! :) I had no idea that piece was so stinkin expensive. The service department is trying to warranty it, but looks like the ride this weekend is out either way! Sucks! I guess that it's better that I found the crack earlier as opposed to later though...

not sure if you've seen this site or not...but try click on "dirtbikes" under yamaha and then find your bike, year make and model....i think the slide is about 90 bucks....I had needed a part one time, and HLSM would not have it in stock for 3 weeks. my dealer matched their price....other than that i've had very good luck with them...Good Luck


Scott -

Might want to try the Carb Parts warehouse to see if they have the slide. . .

(216) 524-1599


'00 WR, YZ modified and MX-Tech suspension;now if I could just ride it.

Well, I got my carb slide installed and bike all put back together..

Started right up !! WOOWHOO! :) I took it around the block a few times to warm it up. It was still popping once or twice on decelation. Normal?

Granted, I'm pretty excited the bike started considering it was the first time I'd messed with it, BUT I was hoping to see a significant jump in performance.


158 Main 168 Main

45 Pilot 45 Pilot

DTM clip 4 DTM clip 3

Fuel screw 1 1/2 Fuel screw 2 turns


I don't see any difference in the way the bike runs yet...


99WR,WR timing,throttle stop removed,Uni filter,E-Series pipe,carbon air box,Pro Tapers,lights removed,YZ tank,13 tooth sprocket


The main jet is expected to be the biggest change. The others are more subtle changes in response.

Would you be willing to take a gamble on the carb needle EKN#3 ?? A low cost jetting improvement when dialed in.

(P/N 5JG-14916-EN)

James Dean

I'll look through the archieves on this EKN #3 to find out more about it, but sure, I'll try it. :) Have any of the other Colorado guys tried this? What can I expect to see different?


99WR,WR timing,throttle stop removed,Uni filter,E-Series pipe,carbon air box,Pro Tapers,lights removed,YZ tank,13 tooth sprocket


The EKN and EKP needles pull harder at mid-throttle.

This is an increase in needle taper providing more fuel between 3/8 and 3/4 throttle. The YZ426 uses this taper. You WILL feel the change. Sometimes I wonder if the YZ426 clutch takes more abuse because of it. :)


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