@gareth_iowc Yes, there is a need for aftermarket CDI's always. The YZ is designed for track use and isn't great for road. Retarding the ignition, smoothing the band out will help.
YOu could also tailor the band to specific tracks.
But as Darty says, you're getting very specialist here. You'd need a dyno to measure the results.
But on the tame DTR's, it's very noticeable difference.