Hi Norm, I've got it to go!
I took the plug out and sat it on the magnetos base plate and span the engine over with the air drill. There is a spindly little blue spark every 30 seconds when rotated at 800rpm. I then closed the plug gap down from 24 thou to 6 thou and now it produces a spindly blue spark on every rotation. It seems way too weak compared to other magnetos I've tested.
Now I'll put the decompressor back on and see if it'll re-start when cold.
