Small Engines (Lawn Mowers, etc.): White smoke from lawn mower, piston rings, carbon buildup

Question
I have a J.D. STX46 lawn tractor with a 14 hp Kohler engine. I just purchased it from an auction and it seemed to be working well for a few days.  I checked the oil level and it seemed like it might be low but it was hard to get a good reading so I added some JD SAE 30 engine oil and it worked fine.  A few days after that, it started to emit black smoke upon starting it.  I thought maybe I put too much oil in because I couldn't get a good reading.  So I decided to drain the oil.  Without the engine even being hot, the oil ran out like water and after smelling it, it seemed to have gas in it.  I put new SAE 30 oil back in (about 1 qt) and after staring it, the smoke seemed less but was white now.  After leaving it stand for a few hours, I started it again and the smoke didn't appear right away; but started after staring the mower deck.  Do you know what the cause for the smoke could be?

Answer
Have you checked to see if there is gas in the oil since?
There could be a few things causing this. If there is gas in the oil, the float may be out of adjustment ( it should set just about perfectly level when the needle is closed. Also, the needle/seat could be bad, causing fuel to constantly pour in with nowhere to go. This may have been an issue that was previously repaired, but without the oil being changed. It could also be a valve guide that is worn and allowing oil to pass through while it is running. It could also be piston rings wearing out which will cause "blow by" of the oil. It could even be as simple as oil/carbon buildup in the motor, or muffler, which means the tractor has probably been sitting for a while. One thing to try, that is very simple, is to go to the parts store and buy a product called "No Smoke" (yes there actually is such a thing). Drain the oil to accomodate the additive, which by the way is like syrup, and then let the motor run for a little bit. I am sorry to overwhelm you like this, but it is diffucult to pinpoint this type of fix without actually seeing it in person.

Good luck!