Reply to greasy Mystic. Thanks for the response.
The engine is solid as a rock and the plugs are new. The wires all read the same resistance. Haven't put a light on it yet but was wondering what, other than vacuum changes, can alter the timing? If there's a computer lurking in this grey market model, I haven't found it or the usual bevvy of sensors to feed it. Any clue there? Could the electronic ignition have a brain (or an attitude)?