Sounds like several things are goofy... what gears are you running? Try 16 front x 45 back, this is generally a good gearset, and came stock on many bikes. Though some had 14 tooth fronts to keep em slow.
if you have 16x45, look at your air filter-carb-exhaust pipe-jetting next. These are all together cause they need to be adjusted together, they are a single system. Mostly they will need cleaning now, clean em up.
Also, do your wheels turn easily, I had a bad rear brake once that dogged my bike to 20.
Perhaps follow the puch owners manual and get it doing what it was supposed to do originally first, about 25-30. It's in the wiki in pdf format.
Clean you carb, and make sure it doesn't leak.
Read the "moped repair" section to find others who are at your level. You gotta get it running right before you can tweak it up.