Ok i misunderstood the question about the air bubble,,, I will call it a gap in the sight glass, on every oil change i never fill it to the top, i always leave a gap that way i can see where the oil is, i learned long ago if you over fill with oil just a little bit the glass will be solid black and make you think its empty when its full..
I will explain again, i simply removed both (Correct) oil plugs along with the oil filter as i have a new filter to put back in, not much oil came out so i looked at the sight glass and i still have my little gap, it's still just above half-way in the sight glass, so now i'm scratching my head thinking why isn't the oil coming out like it has in every other oil change.
I had been planning this oil change so the day befor the change i checked the oil and it was just over half way up the sight glass, right where i filled it the last time, its not burning or leaking any oil, in fact i went for an 80 mile ride that day, no problems at all.