There are always some non carbon deposits when first running an engine be they from the cast iron liner, ali piston or the rings either iron or O Ring.
For an O ring the bore is best lapped to get it as smooth as possible but even then there will be some initial wear on the ring as it beds in, if the bore has just been left straight off the tool or honed then there will be more o ring wear and this could mean the rings need changing a few times as they become flat spotted.
You also find that when trying to get an engine to run for the first time you are likely to flood it on a few occasions and the excess fuel will was any muck out the bottom of the cylinder. As thind bed in the oil content can be reduced and there should be less metal and rubber being worn off the parts as they bed in.
Provided the rings are Vitron as per drawing they should not be attacked by pump fuel or Colmans.
Neil also asked on another forum and I posted this video of another open crank hit & miss engine where you can see a small pool of black liquid sitting in the well below the crank.