I've got one,problem with mine, is that the spark arcs across the glass viewng window .
The later version, had a ceramic insulator that the spark plug lead attaches to .
The one I have, just has a tightly wound spring with a thin insulator on it, it threads onto a short threaded stud that comes out of the clear glass viewing window .
The 'spring' lead then snaps it into the spark plug cap, I haven't been able to get to work correctly .
Need to find some sort of sealant to seal the area where the 'spring' lead meets the glass .
I remember one member here, I think it was semper gumby, has one, hopefully he can add some of his experience .