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XT550 Possible Electrical Short?

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Hi there ... please bare with me, I am not overly technical with some terms as I am new to the cycle world - and starting with a rather beat up Yamaha '82 XT550.


A bit of history about the bike (as far as I know of it) - My brother owned and ran the bike for about 6 months, then it all of a sudden stopped working. It's seen its share of the road from its side as well as rolling when he owned it, so it's pretty beat up in some parts. After sitting for a bit over a year, my husband & I acquired it and have been trying (in vain) to get it running again.


-We can get the head light to work, and tail light - tail light only when the foot break is pressed, or it is set in Park via the key. 

-Flashers don't work at all.

-Ignition coil (and the spare we were given) - test out in range

-Stator Coil and Pulser Coil - test in range and have been well cleaned

-Carbs - cleaned and re-worked

-Electrical wise - seems to have had a wire in the harness that burnt under the cover by the ignition switch (repaired the burnt ends and replaced the connections

-Flasher Relay Fuse - replaced, wires test out in range but still don't work


We have run all of the tests people have said to run, and replaced quite a few of the smaller parts - all we can think of next to replace is the CDI itself ... I wanted to try and build one as a test CDI to know if ours is actually bad, but the DIY CDI for this bike has disappeared off the web it seems.


The only real thing that is bugging me ... the headlight works great, but no other lights work like they are supposed to ... could that fact cause the electrical not give a spark to kick it over? Or could the CDI be so glitchy that it only runs the headlight and some rare times the horn?


Please help if you can ... I'm to the point of doing a new wire harness, but most I have found are on Used bikes ... can't be certain it will work properly (or is it better to make my own fresh harness and that should make things work again?)


Thank you way in advance for any and all help - 



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I would not suspect lighting issues to effect spark.

I'm not super familiar with CDI but I know they are subject to failure and I don't think it is repairable.

Seems like a likely suspect if your coils, ignition switch, and plug and wires are ok.

Wouldn't hurt to start with a new plug as they are cheap.


For the tail light, did you double check it has a dual filament bulb, both filaments intact?

Check the grounds for any of the components that aren't working. Be sure they are clean and make good solid connections. Check ground at the frame for rust and corrosion...
I'm not sure if the blinkers run off the battery or the magneto on this model - might be good to check.


Horn working intermittently sounds like a bad connection somewhere. If the connections on the horn itself are good I would suspect a bad connection in the control, or in the headlight bucket if the harness goes through there.

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Thank you muchacho ~smiles~


We have checked all bulbs, and they are in nearly new shape. We are leaning towards something grounding the wires out somehow/somewhere as well. It seems odd that it has half of the lights and such are not working - and about a dozen local people swear its the CDI and coils causing that even though everything tests out (other than being able to actually test the CDI itself). We hope to pull the wire harness off this weekend and just uncase it all to check every connection/end/wire, and fix anything that is broken or clean spots that are just too dirty

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Hi Kham:


Here's a link to a homebrew XT600 cdi system....it's the same as the XT550 and you might be able to build a cdi if you can etch a board and you have some hobby-grade electronic skills...the compnents are easily available.   Maybe the one you're thinking of.




The headlight runs directly from AC off an  alternator coil and is separate from other lights that work from the battery, it runs all the time the bike is running.  The bike should start and run without the battery circuit working.


There is no test for the CDI...and it was a proprietary system that was powered by it's own source coil in the magneto (to give it operting power) and the pickup was two coils on the outside of the rotor, one that delivered a pulse for idle and low speed with 12 degrees advance and one at 36 degrees for high speed spark advance  (as I recall)....


On the ignition, all you can do is check the power coil and both pulser coils for continuity.  If they are okay, the chances are the CDI is burned out.  There is no test procedure or repair, the CDI box is potted and uses proprietary components.  Even the dealer at the time had to substitute the CDI to diagnose a problem.  The XT550 is noted for CDI problems...too bad because it\s otherwise a great motorcycle.


The horn, signal-lights, brake light and neutral indicator light all run from the battery....usually unless the battery is new and fully charged, there is not enough current from the battery to operate these components without the bike actually  running and making a charge current.


Because the CDI is so unreliable, and expensive....it's common to see XT550/600 with modified wiring, so checking for a stock configuration is a good idea before trouble shooting.  I would concentrate on getting the ignition and the bike running, then move on to lights etc.




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Even if it's kinda beat up, the XT550 is a great machine.

The lighting electrical is 100% separate from the ignition, with the exception of the ground, the frame is still the grounding point for both. Pull all the frame grounds, especially the ones on the spark plug coil and scrub them with a wire brush. Then using something like this:


Air brush cleaning brushes to clean the other electrical connections.


This should help with some of your issues. The CDI can be repaired, but it's not worth the effort. Try using the Transmic 12 degree one pulser coil set up as the bike behaves almost the same with a flat 12 degree curve as it does with the variable one Yamaha created.


Keep at it and good luck.

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You can swap in a cheap cdi off another bike . I tried the cdi off an old mt 50 Honda I had . Connect using the red and brown and you can justify the cdi . this method helped me deduce a bad cdi .

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