My first moped was the exact same as yours. Mine would go 30-32 mph without a problem. Stock. It sounds like it's in need of some adjustments of some sort. Things I'd do:
1. Is the gas good?
2. Is the spark hot with appropriate gap and plug?
3. Is the belt glazed or loose in the CVT (transmission)?
4. Do you weigh 600lbs?
4. Is your carb up to par - adjusted, clean, good jetting, etc.
5. How is your compression?
In other words, do the simple regular maintnence first. It should perform better without bolt-ons.
Good Luck, Spike