Small Engines (Lawn Mowers, etc.): Kohler Command 15.5HP OHV will not start, craftsman lawn tractor, carburator

Question
I have as 7 year old Craftsman lawn tractor with the kohler 15.5 hp OHV, that will not strart.  It leaks gas from muffler or around muffler and blows blue smoke when trying to start.  Also backfires very strongly!  Did a tune up this spring, oil, oil filter, air filter, spark plug and fuel filter.  Any help will be appreciated!
Thank You  

Answer
 Hello Darin:

 The Carb Float Needle isnt Seating Properly and Gas is Flooding the Engine. Change the Oil (there is gas in the oil now), Clean and Overhaul the Carburator and Install a Fuel Cut Off in the Gas Line Leading to the Carburaror. Whenever you are not using the Mower, Turn Off the Gas Flow to the Carb. Hope this Helps. Let me know what Happens, Please.

 Good Luck

 Respectfully

 John