it could be a soft seize if the carb is dirty and not flowing enough fuel. remove the carb, take it all apart, clean it out, put it back together. also pull the head and take a look in there to see if theres alot of scuffing/scratching or if its smooth.
congrats on getting a good solid moped with a good solid motor. they really are just about bullet proof if theyre not the fastest. some tomos rear shocks will fit on it, but are a little long so your center stand wont let the back wheel spin. however they REALLY improve the ride over bumps ALOT.