I have been asking the same question on a 02 FXDL. I had it happen once when the bike was relatively new. Then nothing. About 04 I put in an after market ignition and used it for a few years, then went back to the stock ignition because a week battery cause kickback and i really did not like it, since then it has shut down three times in about a year. I will see if the same happens with the aftermarket ignition as far as i remember it never cut out. I was suspecting the bank angle switch, but now i am not sure.