Riding tractor blowing fuse

Question

I have a 2000 Poulan Pro lawn tractor with the 18.5 Twin V Intek Briggs engine and last weekend it blew the 15 amp fuse. I replace the fuse and it will start the mower and I can use it for some time... but after I shut it down and attempt to restart it, it blows the fuse after the engine starts to run (5-10 seconds). I have looked for any shorts but have not found any... and that should cause the fuse to go immediately anyway. I replaced the seat switch and ignition (matching parts from a like unit) but the same thing happens. I do not know how to diagnose if the voltage regulator could cause this? Thoughts?