I am one of the guys who had the plug fouling problems (01 YZ426). The new CDI instantly cured my bike. The bike would only run 10-15 minutes per plug. The problem seemed temperature related; the colder it was, the quicker it would foul a plug. With the new CDI, I have had the same plug for 20 hours, at least. And the YZF runs great. This was my second YZF, so it was not like I didn't know how to start, jet, or maintain the bike.

Anyway, my dealer swapped my CDI with an 01 bike off the floor. But another TT guy had problems (like you, he also had a friend with an 00), so I checked with my dealer for him. The mechanic at my dealer told me that the 00 CDI was the same as the 01. But then later someone on this site told me that the part #s were not the same. Why not check YOT website to verify? You might search the topics under "fouled plugs=foul mouth" to get the history on this problem.


I don’t think there is any possible way for any harm to come to your ’01 as a result of the swap. The PNs are different, one advertised change was different initial timing to ease starting, but the connectors and mount are the same.

You will probably have to loosen or partially remove the right side radiator to get the harness out, and the tank probably needs to come off to get at the plugs. There are three, one single wire and two large, multi wire plugs, all three are at the end of about six inches of wiring and plug into the harness just behind the right radiator.

Please report back to us if this seems to do any good for your bike. I’m also interested to know your jetting and elevation/temperature that you mostly ride at.

Good luck, I hope you figure out what the problem is w/ your scoot.

I had a bad cdi on my '01 and since I still had my '00 426 I merely swapped it. Made a big difference - no more 'weird' running problems. Plug still showed too much carbon but things were much improved. Yamaha eventually came through with a new cdi.

I've read that the Cdi could be the cause of a poor running 01. 426.I have a buddy who lent me one off his 00 426 for testing purposes. Does anyone know if there is any harm in swapping a 01 cdi with a 00?

I swapped cdi's (01 WITH 00)Friday, The bike started with the first kick...cold!Went for a 30 mile ride on a combonation of tight enduro trails and fast desert stuff.That was the first time since I've owned the bike that I didn't have any problems.Saturday I rode in the mountains 7000'.....NO PROBLEM.The question is do I replace my cdi with a 00" or do I take the chance with another 01"?

You need to try and get Yamaha to replace it first, if not then I'd say buy the '01 part, and keep your receipt.

If that one is bad as well you should be able to get somebody, somewhere at Yamaha corp. to replace it.

You appear to have successfully diagnosed the problem with your bike. Good job. Now you can have fun with it, and that is the whole point, right?

Congratulations Lou, now can I have my CDI back? :)

Originally posted by firejake69:

Congratulations Lou, now can I have my CDI back? :)

firejake, it's gona be tough but i guess!im taking the bike to santa fe yamaha 8-1-2001.lets see what they can do for me.

Man, I dropped my 01' off at my shop here today, I am tired of fighting all these weird running problems we have all heard of (sooty plugs with ash white electrode, jetting that seems to change from day to day, etc). I am convinced after monitoring all these threads that it has to be my CDI. I am counting on that being the problem, I have never woened a bike that was such fun to ride and so frustrating to own!

Originally posted by lou:

firejake, it's gona be tough but i guess!im taking the bike to santa fe yamaha 8-1-2001.lets see what they can do for me.

To see if they'll fix it?

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