Small Engines (Lawn Mowers, etc.): Briggs engine oil out of muffler, briggs and stratton, tune ups

Question
I own a 3 y.o. Troybilt bronc with an 18.5hp Intek Briggs and Stratton engine. In September my son was mowing the lawn. He went about 75 feet and the engine began smoking and leaking oil. I had performed no tune ups or added no oil since the start of summer. (Mow probably twice a month on a 0.27 acre lot). He shut the mower off. I started it up later and it immediately did the same thing. I changed the oil, changed fuel filter, oil filter per book. I started the mower and it began smoking. Within 30 seconds oil began pouring out of the muffler. Any idea of what it could be? I wouldn't think it would be too much oil since I had used the mower several times since last replacing oil.

Answer
Hi TJ
 Several things could be going on here. The first thing I would check is the oil level in the crankcase. A common problem is that the needle valve in the carb malfunctions (does not stop the gas flow) when the motor is not running. The flowing fuel makes its way into the crankcase and mixes with the oil and causes an overfill condition. Replacing the needle valve solves this problem. Hope this helps.