Small Engines (Lawn Mowers, etc.): B&S Engine Smoking, briggs stratton, fog machine

Question
I was just given older Craftsman riding ower with a Briggs & Stratton 15.5hp OHV engine,model #28n707.It ran great for a few weeks but I needed to change the blades, not sure how to take the deck off so jacked up the front end using the muffler as the base. I let it sit until next morning, when I started it, whie smoke poured out the muffler like a fog machine. I actually thought it was on fire there was so much smoke. It backfired twice then stalled.I had to replace the plug. The air filter was covered with oil and there was excess oil in the filter base.I have run the engine several hours for several days and it still smokes. Im hoping its a ring or valve instead of a cracked block. Any idea how to check without taking the engine apart?
Thanks
John

Answer
Does the oil smell like gas.  The carb may have leaked while the mower was jacked up.

Change the oil and refill with SAE-30 weight oil.  NOT 10-30!!

If you have an air compressor remove the muffler and use degreaser or a parts washer to wash out the muffler to remove some oil.

Replace the air filter as well.

Once the oil is changed and the muffler clean start the mower and see if the smoking has decreased.

Let me know what happens.
Eric