New to bikes.

1981 Yamaha XV920R

Picked it up in Madison this weekend. Ran great.
Rode it home and around all weekend. Ran great.

Now this am and all the way to work it kept dying, back-firing and sputering.
Twice when it died I couldn't get it restarted. It seemed as if the battery was dead but then I turned the key off then on and it would restart. Anyone have an idea of where to look?

Bike is in Mequon anyone wants to come look at it. I don't have alot of money to put into right now but if you help I'll buy lunch!