Here is how it works in my area. Motor Assisted bicycles are not regulated. Mopeds and Scooters are. A moped or Scooter needs an annual sticker and you must be over 16 with a valid drivers license to drive one. No Insurance or registration required. No motorcycle M endorsement required either.
Motor Assisted bicycles are not regulated locally where I live so Federal Law kicks in by default. Federal law says less than 50cc and does not exceed 20 or 30 mph "I do not remember which" under power on level ground it is still a bicycle. That is my understanding of the federal law.
Now.. Some Places Actually have laws for Motor assisted bicycles and the seem to try to lump them in with mopeds for some reason. Which they are not. A bicycle with motor assist is much much less than a moped and really is more a bicycle still than anything.
But.. I am no lawyer and I can not give any legal advice. What are axioms to me are not axioms to others or even local police. A general postulate is that if you call your local law and ask for the laws on motor assisted pedal bicycle, and they can find nothing on it, then the postulate is that they are un regulated and by default federal law kicks in. Again.. I am no lawyer.. So.. If you need to , consult a lawyer. See what they say... Or.. Ride and see what happens.. And when Asked, say it is a 48cc. And it is true.. There are no motors that are 80cc. The largest is 69cc. So far anyway.. Sizes are 43, 45, 47, 48, 60, 63, 67, and 69 being the largest. Depends on the factory. I have seen on guy selling an 80cc and he provided bore and stroke and when doing the math I get 79cc. But again.. I have never seen this. I would have to buy his motor and then measure the bore and stroke and see if it is true. And..If so.. His would be the first.. I can tell you, I have done this and have never measured more than 69cc. Ever.. So.. I quit buying and trying. And for those that sell using this information, they are either lying or they do not know what they are selling.. Both are bad news... Enjoy the ride...