Mine, with a rebuilt top end, has been and still is a very reliable moped. Almost 1700 miles since I did the engine without a problem, except for the time a piston ring got stuck.
I blame that on the design of the replacement piston, though. Instead of being the same diameter as the rest of the piston, the area above the top ring is slightly smaller, so the cross-section of the ring is kind of an "L" shape instad of being square.
Carbon worked its way under the top of the ring and got it stuck. The original piston was of a conventional design
Interestingly enough, Kinetic mopeds' replacement pistons are of the conventional design. Kinetic is an Indian copy of the Vespa.