CDIs(capacitor discharge ignition) is what makes our spark plugs spark, but it's rarely mentioned how they actually work. I bet most of us didn't know that making your own would be practical, but it turns out the CDI is a relatively simple piece of electronics.
Rohmell from motorbicycling.com found some CDI schematics and decided to replicate them in reality. If you'd like to venture into building your own CDI, check out his thread for more details!
A warning to those looking to mod their motorized bicycles:
Most, if not all, of the hacks and mods featured on this site were made by individual hobbyists. If you are new to working with 2-stroke bicycle engines, please by aware that there's a possibility that a mod featured on this site could seriously damage your engine. Please don't try any mod from this or any other site unless you fully understand what you are doing. The owner of this blog will not be held responsible for both material and bodily damage caused by performing a modification featured on this blog. Also remember that opening up your engine may void your warranty!