Deposits on Piston Tops

norton bob said:

Those deposits look like tank liner,if it gets on plugs it will not burn off easily.

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Consider finding a good steel tank ? I'll never go back to old glass fiber gas tanks and the toxic cures for their problems.

Steves said:

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?

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I don't think it is an oil problem. There has been no noticeable consumption and no smoke. Running Castrol XL 20W/50, no Marvel oil.

norton bob said:

Those deposits look like tank liner,if it gets on plugs it will not burn off easily.

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The asymmetry of the deposits points away from that, but I will drain the tank and check the inside with the scope. I put 2 coats of Caswell in the tank a year ago and it looked very good after application. Is Caswell known to break down that quickly?

Just to close the loop on this....
I checked inside the fuel tank and as best as I can tell it looks like it did after I Caswelled it last year.
I was able to do a decent job cleaning the deposits off the piston tops using long cotton swabs dipped in gasoline. See pictures. The bike is running great so I will quit worrying about this, other than to tune the mixture after doing plug chops. I also bought the Colortune device and will try that as well.
Thanks for all the help and suggestions.