Small Engines (Lawn Mowers, etc.): 12.5HP Briggs & Stratton Not Running, briggs stratton, rabit

Question
Hello, I own an older Ariens YT12 Model#286707 Type#0439 01 Code#91110511  It was running fine until I put it away for about a month & Will not start anymore. Its getting a descent spark to the plug & getting at least some gas.  I've tried starting it in the Choke Position & Rabit but still nothing. the only way it starts & runs is on "Starting Fluid" until it burns off & then Nothing. fully charged the battery also. any Direction or Replace it?

Thanks
Justin

Answer
Justin
If the mower was running just fine last month, and will not start now the first thing to suspect is that the gas has gone bad.
If it just keeps running worse and worse until it stops (or doesn't start), it could easily be the air filter.
You can also have a Fouled Plug.
Tecumseh carbs are famous for gumming up and the mower may start but it will not keep running.  You need to clean the carb or rebuild it.  
Also if it starts, but doesn't run the problem could come from a Tecumseh with the mostly plastic carb.  The seal between the main jet and the carb bowl swells up and cuts off the gas.   replaced it with a small O-ring.