Motorcycle CDI problem?

Hi,

In my country, Honda CG125 is very popular model. The models until 1990 were equipped with points/condenser and the later models are equipped with AC-CDI.

My friends informed me some strange behavior of the two models, on hilly/steep roads:

The model with CDI, after running continuously for about two hours would gradually loose its power. In other words, when the engine become hot it will loose it power. And it would need a smaller gear to go further.

On the other hand, the old model bike (with points/condenser) would continue without any problem. In facts, some reported that their bike gained more and more power as the engine got hotter.

Is this all because of the AC-CDI? If it is replaced with a DC-CDI, would the problem will be gone?
If yes, which type would be suitable:

a) Simple CDI (DC/AC Inverter + CDI)
b) Multispark CDI
c) PIC based CDI

I would have thought that a CDI system designed by Honda would be bullet proof. With a hot engine, the performance due to the spark would be 100% until the very last minute when the lack of amplitude would cause a miss-fire followed after 30 seconds by a total stop. It could be that the CDI bike is running hotter due to timing or fuel changes, which causing it to loose compression at higher temperatures. Until both types of bikes have been properly checked, it would be silly to "blame" the CDI.
Frank