Electronic ignition conversion help!

help please,
Someone fitted a 12v electronic conversion to my early s3 li 150 and everytime she starts running after a small time she dies and I find I have no spark from the plug, replacing the cdi unit rectifies the lack of spark but I have gone through 5 cdi units now! Is this just a wiring fault or could it be a fault with the stator plate? Bit of a novice so any help would be greatly appreciated.
Thanks
Someone fitted a 12v electronic conversion to my early s3 li 150 and everytime she starts running after a small time she dies and I find I have no spark from the plug, replacing the cdi unit rectifies the lack of spark but I have gone through 5 cdi units now! Is this just a wiring fault or could it be a fault with the stator plate? Bit of a novice so any help would be greatly appreciated.
Thanks