Pics pleaseBlack and sooty plugs does hint at failing primary coils. They do fail in pairs - mine packed up totally within 10 miles of each other. Im still running the original secondaries.
When the ancient secondaries fail, I'm using car stick coils (3 wire type) with HT leads.

Pics please, if its a car stick coil, why cant you just put the coil straight onto the plug ??
Mart

If you are interested in buying a complete set of four used/serviceable PM me