Sounds like your gas tank is not breathing properly. try this: the next time you run the tiller and it begins to stall out, try loosening the gas cap. It should start running again. This means that the gas cap is clogged. Unclog it or purchase another one.
If you are concerned, you can remove some of the oil. Place a pan under the mower and loosen the oil pan bolt but do not remove it completely. Drain a few ounces of oil out and then tighten it up. Be sure to take the wire off the spark plug before you do this. The lower oil level should stop the smoking.
