Small Engines (Lawn Mowers, etc.): Scag 48 hydro with 17 hp kawasaki, blown head gasket, combustion chamber

Question
My mower seems to run fine for 20 minutes then I lose power and I can smell gas.  It appear gas is shooting out of the carb.  I thought my float was getting stuck so I took the float needle out to clean it, still same problem. Oils is old and plugs are old as is the hydro fluid.  

Answer
since you said you can smell gas I suspect ignition coil breakdown.  Spit back from the carb is common but should not be noticeable.  How do you know it is spitting out the carb?  Are you running without an air cleaner or is the element soaked with gas?  

You could be heating up the ignition coil and then you loose spark.  There would be unburned gas in the combustion chamber and would usually cause a backfire. It may be an engine issue too.  How many hours are on the engine?  If high hours have a breakdown test done by a dealer.  That will tell you the condition of the rings and cylinder. Check for a blown head gasket too but this is really reaching for an answer.  If it was an electrical use other than ignition the unit would not slow down and die it would just shut down.  Take a look at these suggestions and let me know.