I have a 1998 Custom Xl1200 Sportster. I've was on a ride and about 45 miles into the ride when the tachometer pooped out on me. About thirty seconds later the engine started cutting out. As I slowed down it got worse. I found that when I down shifted and the engine was at a higher RPM it didn't seem to cut out as bad. I was able to keep it in a lower gear and limp it home. After I got home I found the battery was drained. I charged the battery and started the engine. It ran fine for about thirty seconds and then started missing again. Anyone have a suggestion on where I should start?