Deposits on Piston Tops

NickZ

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While performing post break-in maintenance after top end work on my 1971 Roadster (cylinders honed, new rings, new valves, head gasket, etc.) I noticed ugly deposits on the tops of the pistons. More pronounced on left side but some on right as well.
Does anyone have ideas of what would cause this and what to do about it?
For the last 100 miles I have been running Sunoco 260 GTX Unleaded 98 octane fuel. Carbs are standard Amal concentrics. The bike has been running great. Starts first kick cold & hot, idles smooth at 1000rpm. Good performance through the throttle twist.
I provide pictures below:

2 photos of the left piston:

then 2 of the right piston:
Then this is what they looked like approximately 100 miles before:
Then a picture of how the plugs look now:

Any help is appreciated.
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Why did you pull the head to look ? Lots of work for not much reason . Normally after a while there is carbon buildup and you would scrape it off carefully ( a de-coke ).
 

comnoz

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Just looks a bit rich to me. The insulators should stay white for at least 100 miles and it should be cold blooded for a minute after starting.
 

NickZ

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Thanks for the replies.
Yes, they are scope pictures.
So I guess I can conclude that I need to lean it out a little, especially the left side.
Should I not worry about what is in there? Will it eventually burn off? I definitely don't want to pull the head off if I don't have too.
 
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If oil consumption has settled good after the run in period then I would only lean things out a bit. How many miles on the carbs , needles and needle jets and the needle floats ? If over 10,000 I'd fit all new.
 
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I'll not share pics of my old girl's gutty works and cause a stir if his gets a rise from any of you guys because to me his are almost pristine.... Then I'm roughly at 22,000mi. with 18k of that on the old lead gas, although a lot of it has been burning out since this switch to unleaded for some reason this country boy can't fathom. True I am rather envious of his pistons appearances and I have no shame, but agree they are a tad rich.
 
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IMO the domes on the pistons look “blistered”

I shall ignore the colour of the spark plugs as this is not a plug chop when at a certain rev range .
 
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Oil and/or carbon fouled spark plugs. I suggest you have your exhaust gas analyzed in order to set the Lamda coefficient correctly. Maybe your plugs are a tad too cold also.

-Knut
 

NickZ

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If oil consumption has settled good after the run in period then I would only lean things out a bit. How many miles on the carbs , needles and needle jets and the needle floats ? If over 10,000 I'd fit all new.
The carb bodies are original (18,000 miles) but I replaced needles, jets and stay-up float kits 100 miles ago. Slides are original, but carbs were honed also during rebuild.
 

NickZ

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IMO the domes on the pistons look “blistered”

I shall ignore the colour of the spark plugs as this is not a plug chop when at a certain rev range .
Yes, the blistering look is what concerns me.
 

NickZ

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Do you have any remnants of tank liner in the fuel tank?.
Tank was caswelled 100 miles ago. Before that it was original. It did have a bit of running on ethanol fuel last year before I was aware of that issue. That led to the carb rebuild. No ethanol since.
 
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I think if you had an oil problem then you would see oil in the first half dozen plug threads. Are you using something like Marvel Mystery Oil? They (pistons) don’t look to bad to honest, see loads worse. Maybe a tad rich (plugs) as others have said. Better too rich than too lean though.
 

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