The 064 had the rev-limited CDIC set-up at the same time when the "Red-Light" 066 was in the line-up. The problem was, the metal-flywheel 066s
were breaking cranks on the flywheel stub shaft due to the very heavy 066 metal flywheel and people hitting the chain brake routinely while the
saw was still spinning. The inertia from the heavy flywheel over time would damage the crank. The rev-limited set-up was designed to reduce that.
The 064 didn't have the problem as much due to the lighter flywheel.
The big problems with the CDIC coils are a high rate of failure and the ones that keep going suffer from "brown out," where they continue to
function but the rev-limit keeps getting lower and lower. I've seen a couple that would only allow the engine to max out at around 10.5k.