Easiest way would be one of those scooter cdi's, and just add a hall sensor. You wouldn't have 12v, or any power unless you used a sizable magnet. A simple disk of aluminum with a nice neo magnet embedded in it should work perfect.
I'll figure something out and bounce it around the moped and RC motor forums... I've got a super rat motor that's a 17mm shaft and theirs a moped with some thing close... I really want to see if it can be done with off the shelf stuff or looking like something it's not... I thought about points and condenser the original Russian probably had ... Make timing and dwell adjustments
Really the scooter cdi box with the hall sensor pick up is the easiest. You just spin the disk till you find your timing spot ( little more than that, but you get me), and they are programmable ones out there for decent prices. Just need power is the only downside.
The battery is easy... LoL the range would be limited to the size and how much it used...
A small gen would power it easy, or a large battery, or molded battery packs to look like panels or something. lol
There's no set min or max really it's what it likes... Go up till it starts to fall off then back to where it likes it... Same as the jetting and all that there's a sweet spot... And everything changes a little with all the variables.... It's a constant game of not so good better not so good and back to better... Knowing the base line or middle of the road is where it's at
If we get technical, there is a formula to calculate spark energy in such a medium as we use. They use it when they are designing ignition systems. I can't tell you that formula, but I assure you they don't just widen the gap and see if it helps. They have min and max recommendations because they spent a ton of money figuring it out.
If we were running HEI system, pumping out 500,000 volts, a big gap would be ok. We have 250v coils feeding a tiny cap that feeds a baby transformer. You have to remember these are baby engines. lol
