Today, on the way home from a job interview, my moped had problems...
While it was idling, it seemed fine, but about 2/3 of the way home I lost a lot of power. I mean, it might have been faster to accelerate from a complete stop if I'd gotten off and pushed, it was that weak. Also, it started to sound different (when I applied the throttle, but not while idling). The normal "round" sound of the motor became a lot sharper, if you know what I mean. It sounded almost like something made of thin sheet-metal had come loose and was vibrating against the cylinder head. Nothing appears externally wrong, all the parts are in their proper places, so I'm hoping it's not a bad piston ring or something internal and semi-serious.
The bike stalled out at a light and I couldn't get it to run, so I started walking it. It seemed like it was turning over, but wouldn't quite make it. After a while, I got frustrated with walking it, so I gave it a running push and it started up again. So, at least it's not seized (unless that's going to happen as it sits and cools off).