CDI unit failure

7 replies to this topic
  • raddad1

Posted May 22, 2002 - 11:24 AM


Anyone out there had a CDI unit go bad. I live in the middle of bf nowhere and have no way to test mine, and I'm curious if anyone has had same symptoms. Here's what happened-

The bike- o2wrf was new, and one week old and running like a top it suddenly dies like out of gas. It restarts and idles, but anything over 1/8 throttle it bogs bad. Won't rev over about 2500 rpm, loads up and backfires through carb.

Cleaned the carb several times to no avail. Borrowed a carb of a fine running yzf, and the wr still had same symptoms.

Did a meticulous valve job, was surprized to find carbon on the seats of a 1 week old machine. Failed the leak test too. Cleaned it up like new again, fired it up. Symptoms did NOT change one iota.

TPS checked out ok. Using same good gas as fine running yzf. Airfilter fine. Plug fine.

I guess its narrowed down to CDI? or rings?

Any thoughts?

  • gonzo

Posted May 22, 2002 - 12:54 PM


Change the rings its alot cheaper than the CDI but you may be right. Check the timing too.

  • Ian_M.

Posted May 22, 2002 - 12:56 PM


i have a 02 YZ426 and my CDI & coil went bad. all my problems were was fouling plugs.i tried everything in the jetting department and nothing ever seemed to work. i tried using didfernt oil on the filter nothing worked & come to find out it was electrical the whole time. once the dealer replaced those two items i havent had a problem sence, jetting is still stock, no blue wire mod, no BK mod etc... ian

  • chrisb426

Posted May 22, 2002 - 04:36 PM


My bike seems to be doing the same thing. It is very undependable on starting sometimes it fouls plugs when it runs it runs fine.

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  • skoobeesnak

Posted May 24, 2002 - 06:23 PM


Just a thought. If it is still under warranty (30 days I believe) though most dealers would extend it to help you, jut take it to the dealer and let him sort it out with Yamaha.

  • Ramrod

Posted May 25, 2002 - 02:54 AM


Ian, your problems sound very similar to mine. My bike was hard to start and fouled plugs for fun, sometimes even while riding. It wouldn't idle right either, I have gone through at least 20 new plugs. I took it back to the dealer and they tested everything and just put a new plug in it and said it ran fine.

After doing all of the same tests you did myself, I finally gave them the what for and they sent me a new cdi unit. It ran great imediately. It might help them to print off all you can about this from the archives. I handed them this because we definately are not alone and the Yamaha rep finally admitted to hearing something about CDI's going bad.

When the weather was cooler earlier on this spring, I fouled a few plugs but my jetting is best stock with the jet needle leaned out one position. BK mod was also done, it just makes sense.

Good luck with your bike, once you get it up and running properly you'll love it ... trust me, it's waaayyyyy better than the XR runnin 450.

  • John_Lorenz

Posted May 25, 2002 - 04:29 AM


I agree with Scoobee

If the bike is only a few weeks old then warrenty comes to play. Take it back, There have been posts of bad electrics from time to time so I would suggest you get it to the dealer for a full diag.

I had a CDI unit go bad on me short trakker a 74 yz250. The high speed coil or black box went out. We checked everything until we swapped that out and the bike ran like new. So ther is no telling what will go bad if the CDI is acting up....

  • Boit

Posted May 25, 2002 - 04:32 PM


Unfortunately, there is no definitive method for testing the CDI. The only option is to swap out the suspect unit for one that is known to operate correctly for comparison.

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