giving it some stick???
sounds like it has been overfilled, and blown the oil back out the only route it has. The air inlet. Basically you need to drain some oil off and ensure that it is at the right level. Remember the oil filter/cooler carries about a litre in it, so account for that.
My old valver did it before i rebuilt it, was quite an interesting few seconds of zooooooom, bang!, pssst, (white smoke behind me covering the dual carriage way) cruising to a stop just off a roundabout. airbox was covered in the stuff.