Small Engines (Lawn Mowers, etc.): craftsman mower quits, briggs and stratton, model type

Question
We have a craftsman mower with a Briggs and Stratton 21 OHV twin that quits running after 15-20 minutes as in the other posts.  Once it cools off it will restart. We have already had the valves adjusted (last year) and since it is a twin, both coils replaced (this year).  The problem still exists.  Anything else to try before setting it on fire? Thanks

Answer
When the mower quits, quickly check for spark to see if the engine has spark.  IF it has no spark, I believe there is a diode wire assembly between the coils that may be giving you grief.  Check this out and get back to me with a model type and code number so i can look the engine up for you to get a better idea what we are working with.