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89 XT600 3EW spark issues / backfiring 89 XT600 3EW spark issues / backfiring
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Yamaha Tech Originally the Yamaha XT600 Tech Forum, due to demand it now includes all Yamaha's technical / mechanical / repair / preparation questions.
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  #1  
Old 19 Aug 2021
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89 XT600 3EW spark issues / backfiring
I've owned my XT600 for a while now and i've slowly been working my through its various issues, the one problem i have is backfiring / running hot and i'm hoping someone on here can help.
I've tested the stator coil, pulse coil, ignition coil, plug cap and plug - theyre all within tolerance.
I could be way off the mark here but when i kick the bike over with the plug resting against the block, the plug sparks continuously instead of one big fat spark at TDC.
Are there any other XT owners who could verify whether this is normal before i spend 2 arms and 3 legs on a new cdi?

I've made a youtube clip to demonstrate

https://youtube.com/shorts/qzoXS_Q7Sxg?feature=share

thanks in advance
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Old 19 Aug 2021
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odd, can you confirm you have magneto/cdi iginition (and not TCI)? post a pic of youor igntion box if you dont know the difference...
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Old 20 Aug 2021
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Yes it’s cdi Turbo, see attached picture
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89 XT600 3EW spark issues / backfiring-e682ff0e-a0fe-48ec-b5f9-f79aed0c971b.jpg  

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  #4  
Old 20 Aug 2021
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Quote:
Originally Posted by turboguzzi View Post
odd, can you confirm you have magneto/cdi iginition (and not TCI)? post a pic of youor igntion box if you dont know the difference...
I see where you're going with that question, how is that possible with a capacitor discharge?

Mezo.
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  #5  
Old 20 Aug 2021
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89 XT600 3EW spark issues / backfiring
Hi,
I can't see if the spark is erratic or just fast. The picture needs to be steady for my tired old eyes

Don't know the code 3EW. '89 should be kick-start, but some early E bikes had both, and maybe CDIs. Why? determines speed constancy of kick start / electric start.

The CDI provides a spark on each revolution of the crank. It does look too fast. Maybe you can take a high speed video and then play it slowly :-)

I can't think of any reason how the CDI / trigger can generate an irregular spark. Also doubt the engine could run in any satisfactory way without a timed spark.

My '87 XT will pull well if i forget to open the fuel tap, until it dies, but will backfire on overrun very soon if fuel is low in carb. Lean mixture also a cause of running hot.

If i can't figure out the problem i treat the symptoms and see what happens. Try a richer mixture - raise the carb needle.

Be well'
p
Last edited by pete j; 20 Aug 2021 at 11:28. Reason: grammar
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Old 20 Aug 2021
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like others, am not sure of what i see in that video, almost look like the extra sparks happen when you release the kick lever, not when you step on it.


cant think of any logical why a CDI would release extra sparks.

a TCI could in theory do it if there was some intermittent contact, thats why i asked



regardless, sounds to me lean mixture, not bad ignition.
does it start and idle ok?
was the bike running fine and then started to go bad or was like that since day one?

how is the color of your spark plug?
bike/problem history count when troubleshooting
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  #7  
Old 22 Aug 2021
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Thanks for replying

The 3ew is the XT600 for the American market, it’s registered as an 89 but uses a lot of 84 parts, not much difference in spec just a supertrap end can and some extra oil breather feed in on the carb to appease US emissions.

As for the carb settings I’ve swapped the ydis carb for a new carb from a running bike so I know it shouldn’t be far away on settings.

I can’t start the bike to check the plug as it kicks back like a mule, although it does pop like it wants to start before it kicks back, the decompressor cable is set up to the specs in the manual (0.5mm), but I need to start the damn thing to fine tune the carb..

Hence why all of the above led me to question the sparking, I’d like to know from other XT owners if they’re bike has continuous sparks through one stroke rather than a fat spark at TDC?

In the meantime I’ll try bumping the bike to check the carb, thanks again..
Last edited by Mothball; 22 Aug 2021 at 10:49. Reason: Spelling
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Old 22 Aug 2021
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like i said, when troubleshooting, every detail counts, it's like detective work to trace the killer....


you wrote "running hot" in your 1st post, so sounds like was it running before the problem? from your other comments sounds like it never run in your hands. whats the truth?



to answer your question: you should get one spark per engine revolution.

but you have to understand that its a very odd question.
a CDI needs power from the power coil to psark and that happens only once per revolution, in other words, technicaly it is not possible to have multiple sparks. or at least in my 40 years of experince never saw mutltiple sparks. but who knows, maybe your CDI is possesed



so the only way to see:
1. if you are more or less ok with spark timing

2. to check thats indeed only one spark


is to use a timing gun.



just throwing parts at it like carb, CDI, coil, pickup is going to be hit and miss as well as costly.
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