It's electrical, IMO. Like an MSD failure. It's not uncommon. I don't know how to test for it, though as I've always tried to steer clear of MSD stuff. I've used it in the past and worked on it for others, but I've never really cared for it. Some people swear by it and good for them. I never have. DO you have a points type distributor to throw in and just try? I bet it'll run fine then.
