Oil in Airbox

I have a 500 foreman and had the whole motor rebuilt back in march. I noticed suring break in that there was oil in the air box. I figured that the rings weren't seated yet. Well it stoped for a short time and now it is smoking like a chain smoker. I opened the airbox just to take a peek and guess what...........oil in the bottom of the airbox. What the heck is going on. I have had several motors rebuilt but never had this problem this is driving me crazy.