Small Engines (Lawn Mowers, etc.): coil

Question
I have a craftsman riding mower with a kohler engine . Model 917271061 15.5hp. I have replaced 2 coils on this mower and it keeps burning them out after a couple hours running . engine will just shut off and will not crank . if i replace the coil it cranks up and runs fine for about 3 hours . what would cause it to keep burning up coils

Answer
I have read about defective key switches that allowed power (DC)to pass through the switch to the ignition module.  This can be very difficult to find and I have never seen it but it is possible.

You can check the switch, by ohming it with a multimeter.
You could check to see if there is any power getting to the coils...just connect/wire a multimeter in the shut-off circuit and see if there is any voltage in the circuit when you are mowing.
You could also just replace the switch and see if a new switch corrects the problem.  

I have not read or heard of anything else that could cause the problem other than excessive engine heat but this is pretty rare as well.  I should ask to make sure...does the engine run fine when it runs or does it seem like it runs hotter than it used to?

Let me know.
Eric