There could be a restriction in the intake air box or the exhaust (or both). The vehicle may need to be re-jetted (carb) after the restriction is removed. Years ago I picked up 7 mph on a moped by just removing the baffle in the air box. No re-jetting was required however the noise level did increase. Also, there could be restricters in the muffler that can either be removed, or have holes drilled in them. You can do a google search of removing moped muffler restricters (not necessarily exact keywords) and you can also find a nice performance air filter to replace the existing air filter, which may be very big, and bulky, most likely blocking a lot of air flow, which will give you more power. These are the simplest ways to increase power without serious modification. If you want to go very fast, buy yourself a speed kit. Be aware of your state laws though, laws change when the definition of a moped (no more than 30mph and 50cc) changes. And removing your baffle will probably violate certain noise ordinances. Have fun!