Simple idea from MB scooters. Electronic coils (CDI's) fail every now and then, this can sometimes just be put down to vibration.
 
This rubber fits between the mounting port and coil, use studs, nyloc nuts and washers if you can (or screws) but don't over tighten them so there is some flex and movement in the coil. 
 
Fits all Lambretta and Vespa type electronic coils.