When I converted my last boat to electronic ignition, I had the same issue, but it happened after about an hour of sailing. I read somewhere that it could have been the coil, and the PO didn't really do much with her. I pulled the coil, and the bottom was rounded out, presumably from the heat of the coil. I replaced the coil, and mounted it to the bulkhead, and had no issues since. I think your coil was newer than mine, perhaps that is why it lasted.