CDI was my first guess. I’ve measured several over the years with an ohmmeter and the factory specs and it’s usually really quick to rule out. You should be getting a bright blue spark. Also 8 volts to the CDI could mean there’s a small section of the wire that’s pinched, chafed, or just a low battery. 8v is not enough to do anything. I’ve had to reword several bikes and Fourwheeler’s due to corroded wires. That green crust will cause a low reading as well