Stuck carb float. The float gums up and sticks, and the fuel runs into the crankcase. Contaminates the oil, and overflows everywhere. I had one so bad it filled up the cylinder, and the engine would not turn over. Had to pull the plug, pump out the gas+oil mix, then it would run like yours. If your oil is overfull, and you know you did not overfill it, it is the gas getting into the oil and you need to fix the sticking (or sinking) carb float. I have heard there are Chinese carbs you can get for cheap on the web, if you don't want to rebuild it.
Good Luck!