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Strange spark plug wear? Strange spark plug wear?
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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 31 May 2018
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Strange spark plug wear?
Replaced my spark plug today. I also checked the tightness of the exhaust fittings (headers and clip connecting downpipes to exhaust ) - these were very loose, which would explain some difficulty I have been having with starting it without full choke, even in summer .

The condition of the spark plug seems rather strange to me. I last changed it between 5-8,000 km ago - can't remember for sure. What do you think from these photos?
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  #2  
Old 31 May 2018
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Exactly what, regarding the sparkplug, is it youre worried about?
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Old 31 May 2018
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I can't see your photos clearly enough to tell, but....black soot is characteristic of rich mixture, oily black deposits can signify leaky rings. Is it also worn, as your thread title suggests, in addition to discolored? I can't tell.

Beyond that, you'll do well just Googling for photos to compare with your plug. Back in the pre-electronic era, auto mechanic instruction manuals used to feature these photos prominently, since changing out plugs (and points/rotors, plus adjusting dwell and engine timing) had to be done so frequently.

Hope that's helpful.

Mark
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Old 31 May 2018
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i can see black soot = rich, but not wear. last time you changed your air filter?

other possibilities: wrong fuel level, someone played with the airscrew, stuck choke/choke valve not sealing.

And I cant see how loose exhaust nuts would make it difficult to start, unrelated IMHO.
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Old 31 May 2018
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Overheated/mixture too lean due to leaking exhausts - the whitening of the tip. Replace with new plugs of correct grade. The soot is likely from too much choke - did the plugs come out right after starting?

Replace gaskets and torque exhaust bolts to required spec should do the trick. Be sure to get the old compressed gaskets out of the manifold recesses before replacing with new gaskets; make sure to seat the exhaust headers snugly before tightening - you will need to loosen all exhaust mounting points to do this properly.


Agree also good time to check air filter.


Regards,


Sean




Quote:
Originally Posted by andrew184 View Post
Replaced my spark plug today. I also checked the tightness of the exhaust fittings (headers and clip connecting downpipes to exhaust ) - these were very loose, which would explain some difficulty I have been having with starting it without full choke, even in summer .

The condition of the spark plug seems rather strange to me. I last changed it between 5-8,000 km ago - can't remember for sure. What do you think from these photos?
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Old 31 May 2018
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Sorry, putting "wear" in the title was a bad choice of words. I was referring more to the colour. This was the first plug I have pulled from my XT that has ever looked like this. I replaced the air filter about 100km ago. Will monitor and see whether the mixture issue has been fixed. Thanks for the help!
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Old 1 Jun 2018
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Note that the only useful time to pull a plug to look at it's colour is after a run on the road, preferably at speed, then do what is called a "plug chop" - pull in the clutch at speed, hit the kill switch, coast to a stop and pull it for a look.

Light brown electrode = good, black dry and sooty = rich, black and wet and oily = $ bad, all white = too lean / too hot a plug.

There's lots of spark plug colour charts on the web, have a browse, but note 2-stroke versus 4-stroke is a little different.
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Old 3 Jun 2018
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looks a tad on the dark side !!

But as posted above, if you've just been doing short journeys or pulled the plug after running on choke/cold motor then it's hard to diagnose.


You don't mention what bike.

Carbed bikes often have sootier plugs. They can't control their mixture like FI.

There could literally be 20 reasons why your plugs look like this.
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Old 3 Jun 2018
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Quote:
Originally Posted by *Touring Ted* View Post

There could literally be 20 reasons why your plugs look like this.

Yes, but he tells us the exhaust is leaking/loose and he needs to use a lot of choke....betcha a cold one if the exhaust is properly sorted the problem goes away and the plug goes back to more normal looking (when chopped as per GJ).
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Old 3 Jun 2018
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I must have 20 plugs looking like that knocking around in my garage at the moment. It's all from running the engine up on choke. If it doesn't misfire (less likely with electronic ignition and lead free fuel) put a few miles of normal hot running on the bike and have another look. If it's still black then's the time to worry but from the look of the area round the tip I recon it'll be back to its normal brown colour.
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Old 6 Jun 2018
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Many more at Google under "spark plug wear guide"
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