Small Engines (Lawn Mowers, etc.): gas in oil, head gasket, metal fuel

Question
Had problem, engine stopping while mowing, there was smoke from engine and when I checked the oil, gas had flooded into the oil.
Did the carb kit and line shut off a year ago.
This time it's is not occuring when sitting, it' happening while the motor it running, because after cleaning the carb and changing the oil, it happened agian after 30 seconds - 1 min of running, motor just stopped  Could this be something besides the carb. eg. head gasket.
Thanks
Neil

Answer
If gas is filling the crankcase to quickly the inlet needle cannot be seating.  The first thing to check if this is the case would be the float, inlet needle and seat.  Is there gas inside the float?  To check submersed in water and see if it bottles.  If it does replace it.  They're could be something in the seat.  So be sure that is clean also.

The next place would be the fuel pump diaphragm.  If the fuel pump is a pulse of a pulses from the crankcase operate it.  They're could be a whole in the diaphragm, but unlikely.  From the description you are giving gas is gravity feeding into the carburetor and not being metered..

Even though the carb or service last your it still could be the problem.  If by chance, it is be sure you are not using a metal fuel can to store your fuel.  Be sure your fuel container is plastic.  Hope this helps