They all worked when shipped, some ran for a while and quit..Yours is one of the older ones that works...
Bill is modifying the ones he sends me to take less current than his...I don't shield the plug wire and can use less power..
A shielded carbon center wire needs to have more initial spark to allow for some loss in the wire...
My Zenoah coils have solid copper center wires are shorter and don't need the extra power...