The terms are literally meant to define certain types of vehicles and define whether they're they're subject to requiring license, registration, and or title along with other laws.
MOPED.—Any vehicle with pedals to permit propulsion by human power, having a seat or saddle for the use of the rider and designed to travel on not more than three wheels, with a motor rated not in excess of 2 brake horsepower and not capable of propelling the vehicle at a speed greater than 30 miles per hour on level ground and with a power-drive system that functions directly or automatically without clutching or shifting gears by the operator after the drive system is engaged. If an internal combustion engine is used, the displacement may not exceed 50 cubic centimeters. The term does not include an electric bicycle.
It's not a moped because it's manual with both Chinadoll and a dirtbike engines, if you can make it only capable of going 20mph then it's considered a motorized scooter whether you put a massive sprocket or other means of limiting the speed. It may not be a motorcycle because it's capable of human propulsion, although it doesn't specifically exclude a motorized scooter from that term it's more accurate to call it a motorized scooter, if It can go more than 20 then it's a motorcycle as all other definitions don't fit the vehicle. And by all means for myself I can reserve it to be a micromobility device which under my laws a micromobility device includes a motorized scooter.
That wasn't the point I was trying to convey though, again, people have made these things to be able to go 70 mph and you can put on hydraulic breaks with a bigger disc (even weld the disc's on and or opt for thicker ones) on the front and back (150 bucks) which is fully capable of stopping a bicycle at a reasonable rate even with a 8hp dirtbike engine (as I believe.)
The point is for something that's capable now without registration to be able to register it later if needed if you need to go faster than 20 to stay legal, and again I have no idea what's allowed or not for other people but for myself I will continue to use my bike without registration with the argument that's it's a motorized scooter and I will take it to court if I have to, and later I'll get it registered when I decide to put on a dirtbike engine.
None of us are lawyers and even if I'm dead wrong because I was caught speeding or it's simply a motorcycle I'm willing to take the chance as I don't have many other options, i enjoy making something I can use practically for cheap
and as the posts original question was whether something other than the chinadoll would be more practical, a dirt bike engine was my own conclusion because I believe most mountain bikes can handle the forces and quite simply the evidence that many people can design a bicycle (getting parts and labor) to go up to 50mph while spending even more money to go that fast on a chinadoll than a dirtbike engine
(an upwards of 3k, the engine itself being around 400 which a dirtbike engine is 150, 20-50 for suntour forks which are designed to last a lifetime without it exploding, a decent mountain bike frame or bicycle bit more practical if you already have one, and hydralic for 100)
also a build with a phatmoto could be cheap as I have one and I can tell you straight up it has way better build quality than my mini dirtbike which can go 50.
