Electric is truly the way to go. I've been tinkering with the idea of a 1.5-2kw hub motor and getting a couple of police auction bird scooters to harvest the battery packs from (36v 6ish ah) for my next build. It's not hard to disable the GPS on a Lime or Bird scooter to simply steal the battery but it's not worth the risk to save $150, I'd rather just swap the brain for $20 and sell the whole scooter.
My 48cc engine's pinion sprocket was wobbling, I wanted to true it up, so I elected to remove it with the biggest, baddest slot head screwdriver I had and the pinion bolt's slot actually stripped out. Apparently you're supposed to heat up the pinion bolts now because they red Loctite them at the factory.
So I drilled the damn thing off, pulled the pinion and drilled a 1/4-20 threaded hole in what was left of the remainder of the pinion bolt crank (somewhat off center) and used an grade 8, 1/4-20 bolt and cupped washer to hold the darn pinion on after tapping it into near perfect alignment, well it's quieter and the gear teeth are looking pretty good, so far.
Otherwise the engine has been fairly reliable. It hasn't had any trouble getting started. I credit the Yamaha PW50 clone carb with it's better metering, and start enrichment circuit instead of choke with it's better running. I like that it's happy speed is about 24~27 mph. Seems to get fair gas mileage I'd expect over 100 mpg at the throttle openings I use and pedal assist, I'm getting about 70 mpg average. I don't think they'll ever get decent fuel mileage.
oh you're getting abt the same, little better than I get. my 48 gulps a little more bcs I have #72 jet in a dellorto clone and 40T. most I got was like 90mpg on a long trip but short hops probably only 50-60mpg. my bike's kinda heavy too. the best might be as much as 125mpg on 48cc with tight tuning to cruise at just above the torque peak. but you'd have to have a tuned pipe and a few sprockets to test to get it to that. cost some $ and swapping around
funny fleabay suggested a pw50 carb to me the other day lol