Small Engines (Lawn Mowers, etc.): oil in the air filter, briggs stratton engine, briggs stratton

Question
Hello,
I have a 2008 Craftsman lawnmower (250cc Briggs & Stratton engine)
Last year (brand new) it worked perfectly.
This year it blows oil in the air filter. What's wrong?
(I did an oil change, not overfilled)
Thanks!
Mike

Answer
The first thing to do is smell the oil for gas.  If no gas is present and the oil level is okay, then the oil is coming through the crankcase breather.  Follow the rubber hose on the back of the air filter to the breather.  It will probably need replacement if there's no gas in the oil.