Farm Boy rust in cylinder.

I have just finished my Farm Boy and run it for a short time on Coleman's fuel.
I used Jan Ridders vapour carburettor which is fabulous, easy to make, easy to adjust, and the little engine starts first flick evertime.
Now I am stripping it ready for painting and have found rust on the top of the piston and in the cylinder bore.
Also beads of moisture on the cylinder head (inside of course !)
I am wondering if this is a common problem and if there is something that I should be doing to stop it happening in future.
All ideas gratefully received.
Tony Adams (Scotland)

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Mine dose the same thing, I think it's mostly combustion residue. It will probably just wipe out. I run mine on alcohol which will pull moisture out of the air so when I'm finished running it and going to put it up for a few days, I remove the spark plug and with the piston at Bottom dead center I give the cylinder a little spray with WD40.
Jim

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Yes, that seems the way to go.

I don't understand where the moisture comes from though.

Thanks for the advice, I'll do what you suggest.