1989 Yamaha Virago stalls and won't start

I've got a 1989 Yamaha Virago 750 that's been running fine for two years. Suddenly about a month and a half ago, it stalled while I was riding and wouldn't fire back up. I got a ride home, came back with the pickup and put in the bed and took it home. As soon as I got it off the ramp, it started right back up. Now it will do this every time I take it out of the garage, and usually by the time I drive around the block and back. The electrical system turns on, and all my lights and such work, but the starter won't turn over until I come back to it some time later or it's had a bit of a jolt in the bed of the truck. Any help would be great!