I don't know if it will go fast/far enough to matter, maybe going through the gears would help, but here is a quick and dirty conversion idea that may or may not work if you have a bike laying around and a spare $50 for a trolling battery:
"Oh what's that dear? There's a bike on the front step? Who put that there?" Think she'd fall for it? Being a moped driver I always wondered why I hadn't seen any electric mopeds around. I bet that would be an easier/smaller conversion
main problem that I see is that the starter motor is designed to run for up to 10 seconds at a time, when I've worked on bikes, and ran the starter for more then 10 seconds I noticed that it got really hot, about 30 seconds and it gets hot enough to burn your self on, the bearings and brushes are also designed for short bursts, and not continued running, a starter might see up to an hour of total use befor being rebuilt if you add up every 2 second burst that it's used.
it's also geared low enough that if you are lucky, in 5th gear you might get up to 15mph
Maybe something the size of a car starter would work. If you put a one-way freewheeling clutch on it, then you could run the starter for a few seconds, and then coast, and then run it, and then coast.... The starter could go down where the motorcycle crank is/was.
Being a moped driver I always wondered why I hadn't seen any electric mopeds around. I bet that would be an easier/smaller conversion
I actually have a Tomos Bullet Moped with a bad engine in it. I plan on converting it to Electric in the coming months. I have several options, just not sure how much money I want to drop into it. The cheapest involves using a modified car starter.
That's the plan in the most basic form, but I've got to source a controller, batteries, charger, etc... I plan on mounting the motor roughly where the engine was, and running it off of the original chain drive. I've not sat down and TRUELY figured it out, so I'm not sure what voltage/amperage ratings I need, etc....