Small Engines (Lawn Mowers, etc.): John Deere stalls, backfires, brownish color, john deere stx 38

Question
Eric,

I have a John Deere STX 38 with a yellow deck and 12.5 Kohler engine.  It will run fine for about 15-20 minutes, and then will just start to sputter and quickly die, occasionally backfiring. However, in a few seconds you can start it again no problem, but in another 15 minutes or so it will happen again. I have already replaced the module, the voltage regulator and the spark plug.  The plug does seem to have a burnt, brownish color to it.  Any suggestions?

Thanks,

Owen

Answer
What brand of spark plug are you using?

Have you checked the fuel tank vent?  Most newer tractors vent through the fuel cap threads.  We have found some caps that were not venting enough causing a vaccum to form in the tank preventing fuel from getting to the carburetor.

You can try loosing the cap and running the mower to see if the cap is bad.

Let me know about the plug and try the fuel cap idea.
Let me know what you find.
Eric