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Discussion Starter #1
Removed both exhaust pipes today. Noticed that amount and "kind" of soot in cylinder exhaust holes is very different:

Front cylinder whole is white-ish and does not mark my finger:


Rear cylinder whole however has a lot of carbon-black soot. I can easily scrap a lot of it with my fingernail:


Is this something to worry about?
 

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Discussion Starter #6
All four spark plugs are similar.

My current riding pattern is riding 10 miles to work and back. Once or twice a week. Speeds under 60mph. The bike was not running for the last two weeks.

Here are pictures of rear left spark plug and front right spark plug:

Rear cylinder, left plug, two pics:




Front cylinder, right plug, two pics:

 

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The spark plugs look good to me. Have you noticed any loss of coolant? Just wondering if you have a slight leak in a head gasket that makes one cylinder burn differently then the other.
 

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I am a little confused about the labeling of your pictures.
Are they front cylinder, right and left plug or 2 pictures of the left plug?
Also, how many miles on them?
 

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Discussion Starter #11
The spark plugs look good to me. Have you noticed any loss of coolant? Just wondering if you have a slight leak in a head gasket that makes one cylinder burn differently then the other.
Yes, rear cylinder has a leak in its head.

Coolant level went down about quarter inch during last 6 month (about 1000 miles, not riding much). Before that I fully flushed and replaced coolant.

Also its a first time I'm taking exhausts of, so I don't know since when this discrepancy exist. Previous owners did not maintain the bike very well.
 

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Discussion Starter #12
I am a little confused about the labeling of your pictures.
Are they front cylinder, right and left plug or 2 pictures of the left plug?
Also, how many miles on them?
I took only one plug out of each cylinder - left one from the rear and right one form the front.

For each plug I took two pictures to show both sides of the plug. First two pics belong to the plug from rear cylinder. Next two pics belongs to the plug from front cylinder.

Hope it make things clearer.

And thanks in advance!
 

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That's likely the source of your problem and even if it's not it's something that will only get worse with time, so you might as well fix it. I know you're working outside so doing this job yourself might not be feasible. Can you get access to an indoor garage for a day or two? To pull off one of the heads, you'll need to remove the engine. Maybe someone has done it without removing it, but it would be easier to me to just pull the engine out.

Just thinking you've already got the swing arm and exhaust off already, so doing it now really makes sense unless you've got the rear end put back on. Even if you have I'd still try to find some indoor space for a couple days and knock this out.
 

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OK, back to the original question.

Soot/carbon build up is normal in an engine with a few miles on it.
Your plugs are showing a lean mixture with the rear plug looking like that cylinder might be using a little oil. You might want to fatten up the jetting a little.
Actually, the port showing little to no carbon build up is of more concern than the other...could be a result of the lean condition.
Any driveability issues such as stumbling, backfiring, hard starting, etc.?

Usually a coolant leak into the cylinder will show up as an overheating problem.
 

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Discussion Starter #19
No driveablity issues. Starts cold and hot, runs smoothly in 50-100F climate I have here. I've had an issue with bike not starting when SEMI-hot but it sort of phased out.

OK, so should I adjust my pilot screw X turns in/out to address leaning?

Currently the pilot jet is 5.5 turns out (i.e. if I fully screw it in, it would take 5 and half turns).
My air cleaner is stock and my pipes are S&M (no catalytic converter or anything).

The leak looks like oil, feels like oil and smells like oil.
 
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