Small Engines (Lawn Mowers, etc.): Heavy Oil Smoke, craftsman riding mower, briggs stratton

Question
Have a Craftsman Riding mower with a 16.5 HP Briggs & Stratton OHV engine Model #310707. Purchased in 2001 and not that many hrs on it as mowing season here in NE New York state not that long. Noticed today while mowing that a lot of blue smoke out of exhaust and a large amount comes out when you load the mower down as when getting into tall grass. But then,every once in a while out of no where, you would think someone dumped a cup of pure oil down the carb as the engine almost stalls and the smoke just pours out the exhaust. It then recovers and will run on with the usual abnormal smoke. Had 10W30 in it but changed to straight 30 HD today and same problem. Quick glance at the engine and I notice a small puddle of oil on top the valve cover. Do I have a drain back or maybe breather problem? Air filter looks OK.  Second time used this year.  Hope you can lead me in the right direction. Thanks, Joe  

Answer
Hi Joe,

Sorry for my delay.  It was a busy holiday here.

You might be right.  A drain hole may be plugged.  You could pull the valve cover and take a look.
A ring may have cracked or oil may be leaking past the valve guide.  You could do a compression test also.
 
I am swamped with questions and can't give follow up answers until next week.  Sorry.

Good Luck,
Michael