how can i fix my briggs & stratton quantum 3.5 engine?

hi there i have a problem with my briggs & stratton qauntum 3.5
engine it starts very easy it's usually a litte smokey when first starting but it clears after about 15 seconds the problem is i have noticed oil dripping out of the air filter i was wondering what would cause this kind of problem i don't think the engine is warn it will usually run for an hour without stoping and will start just as easy when warm