Fine tuning suggestions

New WR426 strictly stock except for the W.B. E-series pipe. The pipe improved the perfomance considerably when the weather was warmer in the 60's. Seemed to me that it was running great. I'm at approx 5500'elevation. Now that the temperature has dropped,(now in the 40's or below)the motor is crapping out when I accelerate off the bottom. I'm wondering if anyone has experienced this and could suggest specific adjustments. I guess I'm a little timid of the complexity of these carberators and want to be pointed in the right direction from the start. Also any other things that might unleash more performance.

I'm finding a great deal of info from this website and just want to say I'm really enjoying the entries you all have posted. Thanx Again !


Did you make any jetting changes with the pipe? How many discs are you running? Have you cleaned your air filter recently? Did you change the cleaning procedure? Have you tried a new plug?

We have a couple guys with your pipe and around your atlitude, someone will help. They just may need more info.



86TT225, 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.

I had similar problems with my 99wr. I set it richer, and covered the left side radiator completely to keep the water temperature high enough. I think that the carb in my bike is different from yours so I can't suggest you any numbers of the jets. I've noticed that at least my bike is rather sensitive concerning the outside temperatures and takes few kilometers of easy riding before it has warmed up properly.



Here's my guess (there are more people on this board that have more knowledge). Since you added the pipe and live at a higher altitude, you did not have to make any adjustments. I did the same pipe swap at near sea level and had to richen my jetting. Although you did not have to make changes then, you probably were at the limit of what the stock jetting could do. And now with the lower temp, you have increased air density. This is causing a lean condition a lower throttle settings. Back out your fuel screw a quarter turn at a time and give it a try. If the screw has to be adjusted more than 3 turns out. You should look at increasing your pilot jet. You could also move the clip down on position. Take notes and make only one change at a time.

For trimming the throttle stop. I pulled my carb and did it. I used needle nose pliers to get the stop out and took little bits off at a time and check it each time. I don't recall what the final length was.


Bill and Ande ...

Thanx for your response.More info as you said will probably get even more help.

Air box lid was removed.No jetting adjustments have been made as of yet due to the extreme cold temperatures within past days. 12 discs are on with the stock headpipe. The air filter is religiously kept clean.

Being new to access all the knowledge of others on this site;I like to hear more about trimming the throttle stop and what I'll have to do to acomplish what sounds to be a pretty minor task with noticable results.

For what it's worth, the bike came out of Canada.

Thanx Again

What is your stock jetting. I live and ride at about 5000'. I have the same pipe and run the same number discs. I just went through this. If I can't help James Dean or Clark Mason can I think that they are the jetting gurus of the U.S.


Thanx for your responce.

I haven't changed anything from the stock settings which are as follows.

#165 main jet

Pilot screw at roughly 1.75 turns out

#42 pilot jet

#4 groove on the needle

Anxiously waiting your input.

Thanx again


These are the setting that work for me, but keep in mind that I have a 00 400.

168 Main Jet

45 Pilot Jet

3rd clip on the needle

1 5/8 turns out on the fuel screw.

I can't take total credit for the setting James Dean and Taffy helped me with them. To read the whole story go to my profile and do a search under my posts. It will be under More Jetting Woes and More Jetting Woes Part 2. Hope this helps, Good Luck

[This message has been edited by GRC (edited 01-30-2001).]

I like to hear more about trimming the throttle stop and what I'll have to do to acomplish what sounds to be a pretty minor task with noticable results.

For what it's worth, the bike came out of Canada.

I too also have a canadian WR426, and just so you know it does not come equipped with the throttle stop or removeable exhaust baffle like the american version.


WR426 Power!

I believe all bikes have the stop screw. It is just that some have a longer stop than others.

Pull the airbox boot off of the carburator and have someone open the throttle all of the way. If the throttle slide lifts only half way through the throttle body, you need to trim the screw.


I agree that the pipe has no removable baffle, but after seeing the photo on this web site I am wondering if for some reason was there a different carb put on my bike.

Am I mistaken or is this not the throttle stop which his arrow points out.This looks identical my carb.

GRC....(Or Taffy or J.D.)

Finally getting back around to dealing with the tuning thing again.I took your advise about changing the jetting.I found that was even worse.I can't explain all this.Very frustrating for somthing that would seem so basic.

The plug readings I'm getting are still black and sooty no matter what I seem to try.

I guess I'm still rich.I believe these carbs are set a little rich to begin with and that is for sea-level and standard conditions.It seems to me that your suggestion was to richen it up more instead of making it more lean which is the way I've learned to change with alltitude.I understand that the pipe had a great deal to do with the whole thing,but looking back the bike ran great with no jetting changes and simply crapped out as soon as the air got colder.

I'm going to go the other way towards a #162mj and try that.

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