Small Engines (Lawn Mowers, etc.): TroyBilt Mower engine smoking, briggs stratton engine, engine model type

Question
I have a TroyBilt Pony 17.5HP 42" cut Lawn tractor (model number 3712013AN689G766  Serial number 1D224B80043022). It has a Briggs & Stratton engine 17.5hp OHV (Engine Model/type/code 31C707/0154E1/040420ZD). Early in the mowing season (early March) I began experiencing problems with the engine sputtering and smoking. I proceeded to do some maintenance on the engine. So, I changed the oil and put in a new air filter. It ran ok for a short time, then began experiencing the same problem again. I called my Dad to come look at it, and of course that day it ran fine...no smoke, no sputter, so I continued to use it. Last week I go to use the mower, and WAA-LAA...it was hard to start, smoked and sputtered. So I shut it off and put her away. My Dad came back today to look at the mower again. We drained the fuel tank, removed the spark plug, removed the valve cover and gasoline began pouring out. We then drained the oil and found it to me full of gasoline as well. About 3 months ago (in early March) our local Marathon/Speedway gas station posted a sign about high ethanol content in some of their gasoline. I disregarded as I had not experienced any problem at that time. After the initial "maintenance" was done to the mower and it was still running poorly, I began to wonder if THAT gasoline may have damaged my mower. So, I guess my main question is....can high ethanol content (>10%) cause damage to my lawnmower engine and if so, are these symptoms common? (Difficult to start, white smoke, and engine sputtering and will not stay running). I should add, there was NO GASOLINE in the oil when it was changed in early March.
I must also add, this TroyBuilt is 8 years old, but has been VERY WELL taken care of. I have a small yard, so one tank of gas usually will last me for 4-5 mowings.
Thank you so much for you assistance in this matter.
Barb

Answer
Barb
What your problem is your carburetor float is sticking allowing fuel to by-pass the carburetor there fore dumping fuel in to the engine because this is gravity fed and the tank is higher that the engine so it has to go somewhere,it is flowing pass the piston rings and in to the oil. This will ruin your engine because you no longer have lubrication for the engine. Remove the carburetor Make sure you document how everything is attached use a camera or a pad & pencil because when you go to hook it back up you may not re install the way it was. If you feel competent to rebuild the carburetor you can buy a kit you will have to clean the carburetor really good and soak it in a cleaning solution. If not take the carburetor to a dealer and have them rebuild it they should have all the parts and cleaning tanks. A new carburetor will cost you from $60.00 up to $80.00 Depending where you buy it a New kit  is around $45.00 depending on what carburetor you have it is either a (Nikki Carburetor)or a (Walbro Carburetor) You need to look at the carburetor it should be stamped on it.We can get you what you need for the carburetor,we are a authorized Briggs & Stratton Dealer.Our web site has help on carburetors also.