So this is kind of a follow up on my plug fouling issues I've had since I bought my bike on 5/12/01. I had a lengthy conversation with the president of CO Powersports over my lunch break today, I'm not really a happy camper. Kurt cannot figure out a decisive answer as to how to fix my bike. He was at least very open to talk with and seemed somewhat concerned. However, he says that he's in a tough, middle man, type position on this in which he is only the seller of the bike, not the manufactorer. He doesn't know what to do because so many 426 oweners do not have any trouble with their bikes. I told him "that is exactely my point".

He then went on to saying that I have to understand that this is a competition bike, and is meant to be ridden around in circles on a track, and that the only people who experience problems like me are the ones who use this "racing machine" to ride trails. Is there something I'm missing here, did your shop tell you that you are not supposed to ride these bikes on the trails??? Is this not a DIRT bike? I think this is a major cop out, I know there is a substantial number of thumpers out there that use their bikes also to mainly ride trails as I do, and do not experience the same kind of problems that I'm having.

Long story short, the best he can come up with is to offer me fair market value on my bike on a trade in on another bike that may be more suited to my kind of riding. No, if I wanted a different bike I would have bought a different bike. And he says, do to the shear number of 426's out there now, and the fact that they are not selling them for what they were selling them for 3 months ago, he can only offer me a reduced trade in amount.

Now, come on. There is a very specific reason as to why I purchased this bike, and everyone of you knows what that is every time you sling your leg over your 426 and spin that throttle, it's because they are simply awsome machines! And now I'm feeling very slighted becuse the bike they sold me wont run right and the shop around here "doesn't know what to do to fix it." The fact that an authorized Yamaha shop cannot figure out how to fix a bike they sell, seems very bush league to me. This isn't intended to be a rant, I'm only posting this to find out what others would do in this situation.


They can't figure out whats wrong because they have no way to test the cdi. When a shop fixs something its because they tested it to be broken and they replace it. The cdi's on these bike have no test to run on them for fault codes. The only way to know what it is,is to take a brand new one and put it on and ride it around the block. If they don't want to do that for you because its a new part thats fine to.

Give them your cdi and ask them to put it on one of there bikes and see what the outcome is they will be suprised that there bike now runs exactly like yours and maybe if they are smart enough they can put two and two together and solve your problem.

Bike shops are reluctant to have a customer that knows more than them so humor them and tell them what they want to hear. Or act dumb with a lot of pointers and maybes.

HEY! tell that dealer you want him to call yamaha and approve a new CDI, mapping circuit, and carb. My dealer did that for me and yes, it was after the lame 30 warr. What is up with that? 6,000$ and no warr. any way the new carb will fix your bike, it did mine.

This guy just doesn't want to deal with yamaha. :) :rolleyes:Make Him!!!

Nozzlejockey is right. Make those jerks replace parts until it runs. Start with the CDI. DONT let them give you trade in and make more money off you. Continue to be a thorn in their side.

You can use my name with them. Joe, the manager, and some of the mechanics will know who I am. Because I was a pain like you need to be. I bought a 99YZ400F from them when they were Boulder Yamaha (It ran perfectly and NEVER fouled a plug in two years). When CoPo took them over, they jacked their prices way up. Alot of the good people left. So I bought my 01YZ426 mail order. Of course I had the CDI problem, and they could not fix it. After many jetting visits to CoPo, Joe finally told me that they could not help me because the needle they needed was on backorder. I knew that was just his way of telling me to get lost (thumpers arent that sensitive to a minor change like needle taper). Fair enough, I did not buy the bike from them, they don't owe me. BUT YOU DID AND YOU HAVE LEVERAGE!

I went to Twin Peaks Powersports, (Rt 66 and I25). They ripped a carb off a floor bike and let me try it. No dice. Then they swapped the CDI, which fixed all my problems with the bike. ALL THIS FOR NO CHARGE ON A BIKE I DID NOT BUY FROM THEM! So a couple months later when I decided to get a WR250F, guess who I bought it from?

My friend Jeff Bratton bought an 00 YZ426 from them and had the same problems. They would jet it, he would take it to the track, it would foul a plug after 1 or 2 laps, and he would take it back to them. After 3 months he made such a big fuss that they gave him a new YZ250 in exchange (we had not figured out that the CDI was a problem yet). He took it down to the Honda dealer and traded it for a CR, he said he was finished with Yamaha. Until he rode my 01, then he went back to CoPo and got an 01-and it was a plug fouler too! After the standard jetting rigamarole I told him to make them give him a new CDI. All is well now and he loves his bike.

As you have figured out, the answers you have been given are bull$hit. They know damn well that plug fouling is an issue (I only ride my YZ on MX tracks, and Jeff mainly rides tracks, yet plugs still fouled). CoPo needs to go to bat for you on some parts swaps with Yamaha. Don't give up, be a pain!

If they don't come through for you in the end, let us all know. And I will swap you my CDI for a day to see if it fixes the problem.

By the way, is the bike stock? Stock exhaust ever been removed?

Ok, I went through the whole drill on this but you might not like the answer. You could have a bad carb or bad cdi or both but there's a good chance that it's neither and you'll have to live with it.

First, I have owned the (recently) the '98 YZ250 (2s), the '99 400, '00 426 and now the '01 426. I mention the '98 because that bike also had some problem that prevented me from being able to lean it out properly. Never figured it out but no jetting change did the job. The '99 and '00 bikes were perfectly jetted and responded to changes as you would expect - no problems there. The '01 has been a completely different story.

I fouled the first plug even before the first ride - in my garage - but I think that was due to a big change in the carb choke/pilot circuit from the previous years. The '99 and '00 bikes liked to have 2 hits of the throttle before the first cold start of the day - then 1 kick to start. When I picked up the '01 I did the same thing but it wouldn't start (this is at the dealer - they gave me the honor of the first start). I probably fouled it then as I've found that any throttle during start for the '01s is very bad. The first month I had the bike I fouled several more plugs and tried severe jetting changes (38 pilot, clip up 2, 158 main - in winter!) but without improvement. At the same time I noticed some really weird running behavior: within a few minutes after first starting and riding the bike it would start popping/backfiring and wouldn't idle - as though suddenly very lean. After another 5-10 minutes the problem would disappear only to reappear after a break when the bike cooled off (again in winter). I still had the '00 426 (still can't believe the morons that showed up to look at it when I tried to sell it!) so I swapped out the '00 cdi and -voila! - the 'weird' problems went away. After another few weeks Yamaha came up with a new cdi. The plug fouling was also a bit less but the plug would still get sooty very quickly regardless of jetting.

I did find that if I performed a high speed full throttle run just before shutting down that the insulator would actually be white (=lean) but the metal surrounding it would be black/sooty. So, I learned not to use any throttle prior to starting (as on the '99 and '00 models), turn off the choke very quickly after starting and fouling happens only rarely now. The off-idle rich/burbling behavior has never gone away and no amount of playing with the pilot screw changes that (40 pilot, clip up 1, 160 main - summer jetting). If I screwed the pilot all the way in the bike should die - no gas - but sometimes it didn't; it would run leaner (as evidenced by the typical lean-run on behavior) but not die as it should (leaking pilot circuit?). The really strange part is that the bike seemed to run better over time - less rich/burbley off idle.

Now the really interesting part. After harassing Yamaha for 8 months (bike was bought in November, '00) I was finally the proud recipient of a new carb - no charge- from Yamaha! - in July, '01. Happy days! Problems finally solved!. NOT! The bike ran exactly the same as before; if anything a bit more 'burbley' off idle than with the original carb. So, here I am, not really happy but the bike runs very well and starts easily except for the rich, off-idle behavior.

At this point, I have become convinced that Yamaha over did it in trying to remove the 'bog' of the '00 426 that occurred when you yanked the throttle open. That no longer happens. 1 cde, 1 carb, countless jetting changes and a number of plugs later - no change. I performed every ignition check in the manual and everything else looks good.

In talking with the mechanics at the local dealer (who are pretty good guys, actually) I found that some bikes were terrible! The bikes wouldn't even run! One case was due to the wrong needle being installed in the bike (european spec needle) but 2 others had really bad carbs - the replacement fixed them. So, in your case it could be a bad carb but if your bike runs like mine then it probably isn't.

Good luck.


This is what I would do. I lived in Denver only a year ago and if I still lived there, I would have offered to switch CDI's, Carbs, etc......with you to find the root of your problem. If the AHoles at COPowersports aren't doing everything in their power to help you, then they are a just as bad as most Yamaha Customer Service Rep's. There are plenty of Thumpers on Thumpertalk that live in your area. I'm sure one of them would be more than willing to take a couple of hours to help you out. If I were you, I'd get in touch with one of them, haul your bike to their house and in an hours time, you'll know what your problem is. If not, let me know. I'm in VA. I would send you out my brothers CDI from his 2000 426 so you could try it out.....Just get it back to me with 2 day air and that would be fine. I'm a firm believer in "If the dealer isn't bending over backwards, then they are in the way of progress." :)

Now, you guys know,

I JUST LOVE THIS **** !!!!!!!!!!!!!!!!!!!!!!!

I don't have anything more to add that hasn't already been said/written.

I did like the comment about the bike being intended/able to be used for riding only in circles on a track - more of the same pukey crap the dealers and yamaha use as a "make you go away" tactic.

I'm about to execute the BK carb mod on my bike, cause even with 4 weeks of re-jetting combinations, and a P38, I still have no instant power - I wonder if Ferry would trade me one of his lapped out practice bikes for my 10 hour new one?

Good luck guys......


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