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Well, there are two possible problems. Both are related to bad ignition wires.
The distributor lead has developed pinholes in the insulation, and as a result, leakage or corona effect is occuring ... the sparks you observed at night. If your ignition wires are still the OEM style, you can replace just the black 7 mm Neoprene/Hypalon wires with bulk spark plug wire from a local auto parts supply. Do not buy a generic, unbranded wire. MSD, Belden, Packard, AC-Delco, Bendix-Autolite make bulk wire that can be bought by the foot, and will work with your OEM ends, which just unscrew from the wire. Metal-cored wire, either copper or stainless steel, is what you need to replace the OEM wire with, not suppression wire! I prefer silicone rubber insulation, but black Hypalon is satisfactory if silicone can't be readily found. You will want to test all of your Beru spark plug connectors and distributor connectors for continuity with a reliable multimeter. The resistance of the Beru connectors should be 3000 Ohms +/- 10%. The dist. ends may be resistor or non-resistor type, but the resistor type are usually 1000 Ohms +/- 10%.
The other potential problem is carbon-tracking of the coil output tower ... if the problem has been going on long enough. It would be visible on the light tan plastic of the Bosch CDI coil, which, incidentally, must NEVER be replaced with a conventional coil!! If a dark-colored trace(s) or track(s) can be observed on the output lead tower insulation, then thorough cleaning is needed, perhaps even with abrasives ... in order to remove all remnants of the carbon!
After the above repairs are done, I am sure you will notice a significant improvement in engine performance, but I would recommend having the ignition system tested on an ignition analyzer oscilloscope, just to be sure the coil hasn't been damaged by internal arcing and shorting.
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Warren Hall
1973 911S Targa
[This message has been edited by Early_S_Man (edited 06-03-2001).]
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