oil in yics passage?

I opened up the yics passage and noticed the plug was wet with some oil. I pushed a piece of cloth through the passage which also picked up oil, but nothing excessive. Should I be worried about this? any ideas how it got there?
I recently worked on the valve shims and rebuilt the carbs

 

A small amount of oil collected in the YICS passage is nothing to worry about.

Remember where the atmoshpere inside the passage comes from: it transfers the "waiting" intake charge from cylinders whose valves are closed to whichever one is open, to "swirl" the charge.

Since the breather feeds into the airbox it's not unusual for there to be a bit of "oil mist" in the intake charge, some of which could get deposited in the YICS passage.

 

Thanks for clarifying. I haven't explored the full layout of the yics, is a good diagram around? I think I also overfilled the oil slightly and ended up with some oil in the intake from the breather hose which would explain it.
It had me worrying for a minute there.