cdn. 426 jetting problem ?

Well i am glad to find a site like this one! Anyways, i have a canadian wr 426 that is completely stock. The bike absolutely rips, except for a small jetting problem i think. around about 1/8 to almost a half throttle the engine kind of studders when held at a constant throttle setting (e.g. going down the hwy. at around 50 to 70 mph.) It almost sounds like the engine is missfiring or just cutting out or something. The other weird thing that it does is backfires out the exhaust on deceleration (closed throttle), usually after high throttle settings for longer periods of time. well, i was wandering if there is anyone out there with a cdn wr 426 that has experienced the same problems and what was done to fix them.


my US wr426 does the same thing. if you hold it at a constant throtle posisoion. it will start poping out the tail pipe. no fix found yet. as you go through the throttle it does not do it. it just rips. let me know if you find anything. i am going to go to 1 needle righer to see what happens. i have a EJP now i am looking for a EHP needle.what is you jetting. i have a #165mj #45pj #75paj stock maj and a EJP needle #4clip



not yz timmed yet

some mods

My bike also did the same thing once i put on my WB exhaust and took off my air filter lid. try playing with your fuel screw. I have mine set at 1 and7/8 turns out richening it. if it pops and backfires and stutters it probably needs richening especially on a cool day.


WR426 Power!


I have a 2001 Canadian model and it has the same problems as described above. Are you saying that once you put your WB exhaust the problem was cured? Or is that when the problem started with yours? I have raised the clip position to numerous different positions, leaned out and richened both the main and pilot jets and still had the same problem. No matter which way I went. I could make it slightly better, but never cured it 100%. I am going to buy the Big Gun exhaust and I am wondering if that will be the cure.

Anybody else with this problem seem to have found the answer?

I am going to be taking my bike to ZipTy Racing next week. I have talked to Ty Davis about it and he suggested I bring it up to him and let him ride it. If I get any solid answers I will be sure to post them.


Bob from Aliso Viejo

2001 WR426

I had some problems with my cdn wr aboot (heehee Get it?) a couple months after I bought it. It started sputtering like crazy in the range your talking about. Spent a lot of time in the shop and they couldn't figure it out. It was fouling plugs (have you pulled the plug?). Mine were black as midnight. I (on the suggestion of my brother-in-law, God bless him) dropped the needle one clip. Things have been good since. Look at your manual, they have limited jetting suggestions for problems you experiencing. Good luck, I know it's frustrating.


Thanks for your input. I have pulled the plug and it looks quite clean. The last place I rode was at an average of 9000ft. I had the clip in the second position from the top . (Main jet: 160) (Pilot Jet: 45) I had ridden at that elevation a few weeks earlier with the clip in the #1 position and the Pilot was a 42. In the first described setup, things were 40-50% better.

Can you tell me your jetting and at what elevation you are riding?

I am really hoping that once Ty Davis rides it, he will be able to pin point the problem.

Thanks for everyones help and input from this forum. You all are very helpful!!


Bob from Aliso Viejo

2001 WR426

i found a small cure (well made it better) i went to clip #3 on my needle and it is more responsive. and the poping is much less. i am going to go to 1 needle leaner(obekp)i will let you know how it comes out. you can see my jetting in the earlier post



not yz timmed yet

some mods

Well i finaly got a chance to do some work to my bike (working lots lately-bumber) and i think i am making some headway, although i only was able to take it for a small ride. Anyways, i raised the clip position to no.3 which seems to take most of the stumble away from the 1/8 to half throtle setting. also i backed the mixture srew out to 2 3/8 and it has not backfired since. i am going to do alot of riding this weakend so i should get a better idea on how she is running. i think i might have to go to clip no. 2 to completely get rid of it.

MOJO! u said that you dropped the clip position? this would meen that you richened it. i'm confused this would make your plug blacker. did you really mean raised it. let me know please. Matt.


Brandon: Where do you ride besides raglan & the ganny?

I am the first to admit I'm no jetting master. I've learned by reading posts and being presented with problems. I dropped the needle, meaning I raised the clip position (sorry, that was confusing). I'm running 165MJ,45PJ,ps 1 1/8 turns out. 2000 to 2500 elevation.

My problem was "undetermined" as far as what caused it. It was progressive, meaning after several rides i thought the bike was a piece of junk and it kept running worse. I did give the carb a good cleaning and blow out once I had it off the bike. Might have had something blocking it. It absolutely ripped when i first got it and i don't think i'll ever determine what was caused the plug fouling. FYI- I'm still getting dark plugs with a nice tan tip. This weekend i'll probably go one more clip higher (droppiong the needle a little).

Only mods have been a stock US pipe and airbox lid removed.

WR...going to the #1 position may have leaned it too much. Did you do this mod before you went to 9000 feet?

Matt. Your doing opposing things by raising the clip and backing out the "pilot" screw (you said fuel screw, did you mean pilot?).

Continued good luck. mojo.

I do believe one of the problems qith our canadian bikes is that huge sealed exhaust. What the hell is inside there anyways! I think that it contributes to the popping noises but jetting is more important. anyways are yourunning your bike with your airbox lid off? try taking it off and see how it runs. my bike definitely does run crisper with my WB exhaust than with the beefy original can.

Canuck- I also ride with the OCMC doing harescrambles and a bit of motocross. Me and my buddies also ride the five point trail system near haliburton.

Do you ride in Ontario?

Sorry MOJO, my mistake (just finnished a 12 hour night shift when i read it), i raised the clip one position (no.3) thus dropping the needle and leaning the mixture. I think this is the same thing that u did but u say that you would like to raise the clip one more position. why? Are you still experiencing the same problems because i just went for a little burn and and found that my problem still exists, maybe not to a great extent as before but still there non the less. It seems moreso went i get the revs up. Oh ya, i also turned out the pilot screw to 2 3/8 richening it. Sound like what u did?

Here is a question for everyone with a CANADIAN 01 WR 426. Where the heck is the Yamaha representitive on this matter. It seems that there is alot of people with the same problem and they should be stepping in to fix it or show some support.



Yes and No. Yes I still have some blackening to my plugs and that's why I'm considering raising the needle to the #2 position. No to the 2 3/8 out on the pilot screw. I'm at 1 1/8 leaning out on the low end.

My frustration also led me to contact the dealer in Canada where I bought it. They were pretty disinterested in helping. I found a 1-800 number from a regional rep for Yamaha Canada. The guy there didn't want to do anything but give me a number in Ontario( I think?). Called there and got a machine. Being a Yank didn't help much either. The regional rep said, "I tell the dealers I strongly suggest not conducting cross border transactions" (yeh right...). Don't expect much response Matt. You can learn right here. If my advice doesn't do it, there's someone who can. Hint....try James Dean...he's THE jetting guru....hhhuuuummmmhhhuuuummm.

MOJO, I tried going leaner on my pilot screw (the manual states a stock setting of 7/8?) and found that it just backfired out the exhaust more. Is yours backfireing at all? For that matter is yours also stumbling at 1/8 to half throttle settings, or is it just running rich and causing dark plugs? Mine sounds as if the ignition is cutting out for a split second, i mean a total missfire. let me know. matt.

Mojo- In response to your question as to when I did my mod's......I went to ride at 9000ft in the stock positions. The bike ran TERRIBLE! Through a couple jetting experiments we found that putting the needle in the #1 clip position and changing the pilot to a #40, the stuttering was very minimal but the bike backfired badly. After talking to the mechanic for Ty Davis, he suggested going to a #45 pilot to stop the backfiring. The next trip we did that and the bike backfired much less frequent. The stuttering was still there, but way less obvious.

Next week I am taking the bike up to Ty's shop and he is going to take it for a ride and see if we can eliminate it completely.

Worst part is: After Ty rides it, my bike is going to think it has some pansy a.. on it after that!! Reality really SUCKS!!

I will post my findings next week....stay tuned.


Bob from Aliso Viejo

2001 WR426

Well i went for 2 big rides in the last 2 days with the needle in the no.3 clip position and the bike is running wicked. I don't even think she hesitated or stumbled all day today, just ripped. The next problem i think is getting me a new pipe. My buddy has a wr400 with a pro circuit pipe and we were doing 5th gear roll ons from around 50 mph. My 426 pulled away in the mid rpm range, but as soon as we got the bikes revin he would start to catch me? Also, mine does about 90-95 mph tapped where he is getting about 100. I think that the gearing is the same so i am not to sure what is going on. Anyways something has to be done.

Matt, good to hear your bike is feeling better. FYI....I was still getting some of that stuttering up to 1/2 throttle and last friday moved the clip to the #2 position. Completely new bike. It's back to scaring the hell out of me again.

Bob, I don't get up to that altitude and will be looking for your update.

Cheers, Mojo

Hey guys,

I moved my clip from pos 4 to 3. My bike still has the stuttering problem, and backfires some when coming off of hard accelleration. I see that Mojo went to pos 2 to fix it. It might work for me, but I'm wondering what altitude you guys ride at, I ride mostly from 5000' to 8000'. Mojo, I'm interested in what altitude you ride at.

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