I have seen first hand in the cheaper ebay bikes and also the MSO models and also higher motovert types all thes bikes were rock stock once fitted with a kitaco CDI it made a clear difference nothing so serious as for someone to say holy ****, just a clear improvement on rpm pickup.
You do not need engine work to accommodate a CDI, grab one a good brand perferably you can normally get a kitaco CDI for approx 90 bucks and import loom for 20 bucks
Cheers