Not a problem, but just a bit of a puzzle.
I changed the oil on my K75 and started it up without refitting the oil filler plug. The bike would start up, but refused to run properly or tick over properly. As soon as I replaced the filler plug, all was fine.
Which made me wonder why that was?
I assume it was because of air flowing through the crankcase and then through the breather tube and reducing the vacuum at the thottle butterflies?