Small Engines (Lawn Mowers, etc.): starting problems john deer stx38, spark plug wire, safety switches

Question
I started having a few problems with my tractor. It would runs great then all of a sudden just die, I would get it started again and it seemed to lack power. then it stalled again and I get no spark, at first I suspected the carburetor but it seems to get gas, checked the spark plug wire and the volts to the wire are weak. I then would get a spark and it would run great for a bit then stall out again.
I was able to get my grass cut but then the next day I couldn't get it to run for more than 5 minutes. Last thing I checked last night was the spark plug and it was not sparking, I will try a new plug but I suspect its not that since the plug looked ok.

Answer
It sounds like you have an interlock system short.  These are those lil safety switches that can drive you crazy if they don't work, but are so necessary.

Somewhere on your engine is a ground wire, it should be black.  Disconnect this wire and start your engine.  You wont be able to shut the engine off with the key switch, but what your are doing is separating the engine from the tractor to see if its an engine problem or an application problem.  Make sense?  Check this out and let me know.