A65T with new AMAL Premier, Sparx EI & regulator, copper wire HT leads, no resistor caps, B8ES plugs, Lucas coils (2x12v in series). Bike had fried a Sparx EI module apparently due to a faulty rotor (but in hindsight perhaps a lack of resistor plugs or caps)...it was replaced approx 12 months ago & was starting and runnng very well (too bloody well obviously).

I had done about 50km at 65mph when suddenly lost power with backfire and flame out exhaust (a colleague said flame from left pipe). The bike then began to run rough / missing and I reached down and felt the plug caps, getting a shock from the left cap only). Plug inspection revealed soot / dry left plug and normal right plug. One of the alternator plugs was disconnected but not sure if the was caused during my fiddling on the side of the road. Kickback while attempting to start. If it starts, backfires and runs rough, then stalls.

Back home and can report the following.
Battery holds 12.4 volts. Alternator provides 13.5v to battery so it and regulator OK.
Switched out the Sparx module for a Boyer MkIII with immediate improvement but still runnng rough (not firing on right cylinder).
Brand new battery, new resistor plugs (BR8ES), new 12v coils, new Lucas ignition switch. Cleaned all earths /replaced some earth connectors.
Fixed a wire that had come off of the oil indicator lamp in headlight.
Continuity throughout the system with no voltage lost in ignition switch circuit.
Power reaching EI module.
Both old and new coils show same resistance (around 4ohms I think).
Trigger connections at stator are sound with continuity through to EI module.

This is one of those cases where something simple may have been complicated by much fiddling. I'm hoping some of these symptoms ring a bell to someone and might give me a lead.

Thinking of replacing whole EI (to Pazon Sure-fire) but want to be sure it's necessary.

Any ideas? (I have tried copious swearing).

My Giddy Aunt!