Starting problem, possible bad CDI
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Thread: Starting problem, possible bad CDI

  1. #1
    Junior Member lumpee's Avatar
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    Mar 2019

    Starting problem, possible bad CDI

    Hi all. This is my first post on this forum. I've had a 2005 TW200 for a few years now and it's been a pleasure to ride. It was running fine until recently. I took it in to a local mechanic who pulled the carb apart and replaced bad O rings and it ran fine for a few months. It started easily, but recently it's been refusing to restart while hot. After a few times of that, it now doesn't seem to want to start at all.

    I've pulled the plug to check for spark and find that there is a good spark, but only for two revolutions and then the engine continues to crank, but no spark is produced until I let off the starter and I see one more spark. The sparks are bright white/blue so not weak. Research on this forum lead me to believe that the battery was not supplying enough voltage during cranking to create a spark so I tightened/cleaned connections and fully charged the battery. It now cranks faster and stronger than ever, but the problem persists. Battery voltage remains around 12.4-12.5 even after attempting to start, so no problems there.

    I ran through the ignition system troubleshooting in the service manual and all of the coils showed resistance within range. I have not tested any of the cutoff switches mentioned but I assume those would result in no spark at all.

    All signs at this point are making me think the CDI box must have gone bad. Is there anything else I should check? If not, what's a good way to test the CDI? I'd like to know for sure before I spend ~$200 on a replacement. I will be pulling the CDI tonight and opening it up to check for any broken solder joints or burnt components, so it would be helpful to know if there is a common failure point in those.

    Thanks for reading, I'm hoping one of you TW gurus will have seen this issue before.

  2. #2
    Senior Member assquatch20's Avatar
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    Jul 2010
    An ignition coil is prone to working well until it gets hot. Consider swapping that out. Safety switches could always benefit from being cleaned though. I'd try that first for peace of mind.

  3. #3
    Senior Member Peterb's Avatar
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    Apr 2011
    North Bay, Ontario, Canada
    lumpee I hope you are able to solve this problem and you might be right about the CDI. Lots of TW owners have had a similar problem including myself. Mine has always started before I got the chance to diagnose it. Everyone will tell you that you need a super duty battery, spark plug, bigger jets etc but I have not heard of anyone actually diagnosing and fixing the problem.

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  5. #4
    Junior Member lumpee's Avatar
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    Mar 2019
    Thanks for the tip. I think I will try a replacement even though it ohmed out correctly if I don't see an obvious issue with the CDI. They're under $10 so it would be a cheap try.

  6. #5
    Senior Member admiral's Avatar
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    Jul 2010
    Frosty Hollow
    Similar to what Assquatch mentioned but my Pulser Coil (down by the stator) went bad. When it got hot it wouldn't start/run. Once cooled down it would start back up. It got worse as time went on and then it wouldn't start at all. I did swap out a known good ignition coil so that was ruled out. I then swapped a whole side cover w/stator/pulser coil and found the pulser coil was my problem.

    The Pulser Coil would test ok when cold. I watched a Youtube video of a fellow showing that a pulser coil would test ok when cold and not when hot which led me to replace the Pulser Coil. It has run great every since.

    Although it takes a bit to take apart if you have a buddy who has a Spare TW he/she could load you their Pulser Coil. A Pulser Coil cost $55 ish dollars at Rocky Mountain ATV/MC so you kind of want to make sure it's the coil before purchasing one just in case it's not another component.
    Badgerflorida likes this.
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  7. #6
    Senior Member Sthrnromr's Avatar
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    Oct 2018
    Rural, South Carolina
    Well, if you find out it is the CDI, be sure to grab a new and improved model here =) --> $195 shipped.
    DANo896 likes this.
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  8. #7
    Junior Member lumpee's Avatar
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    Mar 2019
    Well, I got the new ignition coil and it did not fix the problem.

    Can anybody check on their working bike what the output from the CDI is? When I put my meter on AC and go from the input on the ignition coil to ground I get around 7-8 volts AC as the reading while cranking, but it fluctuates a lot.

    I'm going to try to get some readings to see if there is any voltage drop when cranking to the CDI/electronics before I order it. I also posted online locally to see if someone will let me borrow a CDI to test with.

  9. #8
    Junior Member lumpee's Avatar
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    Mar 2019
    An update on this, I did eventually get the bike going. I suspect the issue was caused by a poor ground connection. After reseating the ground connector under the seat and tightening the main ground to the frame, the bike runs normally again.
    Miaugi, Sthrnromr, Purple and 2 others like this.

  10. #9
    GOF is offline
    Senior Member GOF's Avatar
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    Dec 2018
    Buffalo, NY
    Thanks for the update. Always woth checking the grounds and often overlooked.
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