BlackSunday,Go back to your stock settings,any further changes make one at a time.The free mods are great,do them and evaluate your jetting.I believe a lot of this jetting/mod talk confuses alot of people.I personally have tried different jetting,BK mod.I cant improve on what I have.I own a Canadian WR426, '02 model.No throttle stop no blue wire,and sealed euro pipe.This thing rips with stock jetting.I removed the air box baffle and cut 4 holes in lid.Then added a Uni-Filter.I believe not all bikes need all mods,but dont get discouraged these are great machines.Oh yeah if your going to do any work around the carb get a Kouba tool for your fuel mixture screw,great fine tuning tool.BLUE BEASTS RULE

Originally posted by blacksunday12101:

ps dan what about the ACV MOD did you or have you tried that one.

Hmmm.... Im trying to think what that stands for. Which one is that??

well dan i guess i will go back to stock main jet and put the needl clip back to the middle and see what i have with the bike then the only mods i will have is airbox lid off baffel out grey wire disconected and yz throttle stop and see what i get i am getting pretty good at removing the carb at this point it only takes me minutes to do so i will try that tommarrow and let you know its raining now so i cant test it any way.

The ACV or (Air Cut Valve) is located on the left side (Shifter Side) of the carb on WR model's. The purpose of the ACV is to regulate the injection of air into the mixture when cold starting the bike. It also has a minor application during idle operations. The problem is that Yamaha starting with the 98 model WR jetted these things way too rich (65 SJ/90-100 SAJ). Removing the ACV does several things. First the carb breathes better. there are two vaccume lines on the carb that must be sealed with vaccume plugs from the auto parts store. The only real adjustment that needs to be made once the ACV is removed is to the fuel screw (opened a little). When the ACV is gone you can then manually jet the bike for maximum power.

I don't have my data on the 2002 available. If you look at the carb and their is a round vaccume module mounted to the side with three vac lines attached...two to the carb and one to the intake manifold then the answer is yes you have one. If the side of the carb is clean and you can read the Kehin name on the carb you don't. 98 and up.

Keep in mind that somewhere along the line (like on my '01WR250F), the vacuum lines and air circuit from the intake were integrated into the carb body (i.e., no hoses). The function is still the same, but disabling involves blocking off ports that are now completely inside the ACV cover. Do a search on ACV as there is some discussion on this around last fall I think (check the 250F board as well).

well although this bike is brand new i am begining to believe i have a timing problem because no matter how i jet it with the airbox off it i see fire shooting out of the carb wouldnt this indicate a timming problem could the cdi be bad or the cam timing be off i do have the grey wire disconnected i am going to pull the cam cover off and check the vavle clearance and while i am at it i think i will go ahead and yz time it it is just advancing the exhaust cam one tooth correct? wouldnt the fire shooting from the carb mean it is fireing with the intake valves open?? or could this be an indication of a way to rich mixture??? i put the jetting all back to stock and the condition still exists air box off baffel removed throttle stop trimmed and grey wire disconnected also acv defeated by turning the diaphram over i really need some help here!!

[ July 28, 2002: Message edited by: blacksunday12101 ]

BlackSunday, At any point did you or someone else take the slide out of the carb (just to look at) or adjust the needle?? I bet you did... Did you put the slide-plate on right side up??? That's what it sounds like to me.


the needle has been adjusted and also put back to the original position but the slide plate has never to my knowledge been out unless the dealer did it but i assume this is already factory assembled yes?

BS, That silly little plate could be on upside down. If you're going through the carb today make sure that it's correct!! It's goes on the opposite way that it looks. Just make sure, look at the manual. Many guys have made this mistake including myself. dl

i have come to the glaring conclusion that there are far better carbs in the world than this piece of sh*t that came on the wr i have never had the kind of trouble with a carb of any kind that this nightmare has given me if i wanted somthing to work on all the time instead of ride i could have bought a harley flame away i am not impressed! i may have a barley used only 10 miles on it wr426 forsale real soon.

[ July 28, 2002: Message edited by: blacksunday12101 ]

TMR series Mikuni carburetor: (36mm dia. for the 250, 38mm dia. for the 400 and 41mm dia. for the 450); thanks to the close collaboration between Husqvarna and Mikuni, the TMR carburetor has been installed on an off-road motorcycle for the first time. (The TMR series has previously been used only by Superbikes). There are many technical characteristics that make this carburetor the ideal choice for these new engines: a flat slide valve that allows a better power distribution thanks to the reduced interference of the valve on the air flow, an accelerator pump that improves the engine's reactions and power distribution with respect to throttle commands, and a TPS sensor (Throttle Position Sensor) that determines the throttle position and interfaces with the bike's ignition module to optimize the ignition mapping.

wonder if this would work on my wr very similar motor design and at least i can work on these carbs lol

Originally posted by blacksunday12101:

it is stamped with an M. i am assumeing this goes to the motor side also wouldnt it be installed so that the bottom profile matches that of the bottom profile of the slide


Turn the F****R upside down!!!!!!!!!!!!!!!!!

well in that picture and in the one in my manual it shows that the end with the hole in it goes tward the bottom of the slide thats the way i have it i guess i could flip it just to see but i have it the way the picture shows and that is the way it has always been

it is stamped with an M. i am assumeing this goes to the motor side also wouldnt it be installed so that the bottom profile matches that of the bottom profile of the slide ie the flat side down that has a small arc in the middle versus the pointy end looking in the manual this also appears to be correct and there is a hole in the center of one end this is the bottom and that is the way it is installed there is another theroy out the window i wish it could have been that simple but unfortunatley it is not that.

[ July 28, 2002: Message edited by: blacksunday12101 ]

well i just ordered jd`s jetting software when i get it maybe it will help me solve my problem i sure hope so!!!!

Before you drive yourself completely nuts, put everything back as it was, make sure it runs as good as it did. If it doesn't, you'll never get it right because that means it's not a jetting problem.

Try self control, get it going as it was, then do 1 mod at a time. You'll find the problem quickly that way. It's hard not to do it all at once, we've all been there.

It's hard enough to judge the best jetting on an unfamiliar bike. Don't make it harder on yourself.

well in that case i will have to make the first mod be the throttle stop cause i already cut that

That's the idea. It will save you headaches and help anyone else answer questions if you have them.

It's a pretty safe bet that the throttle stop mod is fine, but it's not much extra effort to start there. Run it, then on to the next...

I'd suggest saving the wire disconnecting for last.

Here's why I think you should go back; Stock bike IS restricted, and a dog compared to one that's been opened up. Some guys had trouble fouling plugs. Most had good luck with 3 mods- airbox lid off, throttle stop cut, and baffle out or exhaust upgraded.

If it doesn't run OK after those 3, something else is up. It may be rich, but for 2 years rich was the "hot" setup :)

Even the yz/wr timing shouldn't hurt the power much. UNLESS it got botched and went the wrong way. You didn't mention timing change though.

Let us know how it's going OK?

can anyone post the stock jets and needle for the wr426 it seems my dealer gave me the wrong service manual he gave me the yz manual by mistake thanks for your repley

I think the stock jets are:

42 pj

75 paj

165 mj

200 maj

DRR needle clip #4

Hang in there, I struggled with mine for quite a while, It is well worth the effort to get it sorted out.


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