@Wentwest, Most of what I have are AC 5 pin units with a light green plug. I believe these are made to work with a mechanical advance. I also have some AC 6 pin units. But I think neither have electronic advance.
@KBongos, to answer your question, supposedly the similar looking but larger bodied 4 pin DC CDIs on ebay ($10 to $12) have electronic advance. I have not confirmed this on a running engine (i.e. watch the timing with a light as RPMs increase), but from what I've read.
My guess as to why I haven't seen many AC CDIs with advance is that it may be difficult to power electronics from the AC generated voltage and a digitally controlled CDI may need 12V battery power. But I am not familiar with everything out there in the CDI world. Related to that thought @LongDistanceRider that method of timing advance (two triggers and dealing with the two signals and adjusting in electronics) is interesting! Never would have thought of that. The electronics are pretty low part count. I think the newer CDIs have around 40+ parts inside. I'll bet the old ones last longer.
@777funk, My understanding of the DC CDIs are they include an additional voltage step-up converter(compared to AC CDIs) to get the higher voltage, and this would account for the larger package. The DC CDI is also more universal(assuming you have a battery, decent regulator supply) and could replace a AC CDI system, so maybe more common. I don't trust much I read, there is a lot of mis-information with this sort of thing. You can also switch to newer TCI(not CDI) that just works off 12v. But this may need a different coil or better regulator. Some good sources of information are from people that sell replacements like Ignitech(
https://www.ignitech.cz/en/) has some good info. This guy Thierry in France
https://transmic.fr/ that has got some interesting hobby for sale efforts, one is a programmable DC-CDI using WiFi micro(ESP) for advance table. And there are other vendors.
Some of what I read from Thierry is that there are some motors that offer a pulse signal at advance position, and then a simpler controller(analog or digital) can just add delay to implement a kind of advance. I don't know how common that arrangement is, but it might be what is used for these generic DC CDI's that claim to offer advance. He notes that changing polarity on a pulser(coil) can change timing - they tend to put out a positive and negative pulse signal of some length.
On my bike I put a cheap AC-CDI with a switch that routes it to either 43deg adv or 15deg start pulser signals. Starting is important to have at the retarded position, but once it is running, mine is pretty happy on just the advanced 43deg point. On a few mistakes starting at advance position, it made some complaining noises, but I have not blown my engine yet. I think the starting 15degree or so position is most useful for starting, especially if you had a kick start to avoid kick back misfire issues if a module miscalculates things. And it is important for kick start to fire first few rotations. If I run down the road at 13deg, it is a dog and top speed is very limited.
Here's a few discussions I found searching on the CH250:
https://www.advrider.com/f/threads/elite-150-and-other-scooter-owners-beware-of-cdi.643822/
Elite 150 and other scooter owners beware of CDI!
https://www.advrider.com/f/threads/2-stroke-cdi-on-4-stroke.1122780/
2-stroke CDI on 4-stroke - discussion of CDI with advance.
