if you go across usa on a ebike, it will take you months lol, battery charges longer than it runs. and if you use a solar and 5v to 42 booster to charge, lol, people do not live that long.
Use your gas moped. you can always keep a gas can on your luggage rack for those roads that have nothing for hundreds of miles. I had a bike with a motor like yours, probably 35 years ago, they really did not change much over those years, they are pretty reliable when installed correctly. i'd be more concerned about the bike itself than a motor.