Other than the oil does it seem to be running ok? (i.e. - is it bogging coming out of corners/feeling a bit sluggish etc?) It might be worth having a little play with the jetting/mixture, but if bike seems to be running ok then I'd only do minimal changes bit by bit and keep re-assessing as you go.
Spags - in your case it's cos you're not revving it enough. Happens to all Novices that
