I have used a cdi from a Honda XL600R the advance comes in quicker and has more total advance, I have heard of XL400 cdi being used. You can get even more total advance changing the timing trigger on the crank, NX and FMX have quite a narrow trigger, the XBR and XL's have a wider trigger and the XR is the widest this gives you more total advance, I have seen ones welded up and ground to shape. There is no way to change the factory advance cdi curves, but there is a Czeck company making fully programmable ignitions