Whipped injector leads off to identify cylinder, No4, whip out plugs all Clean and non fouled, but look a little rich, put back some normal ones single electrode and alls well again! leads and cap all checked OK.
Also though I'd take the oportunity to check Adrians point on injectpor pattern so whipped out the rail and fitted it up to a spare pump and Outboard fuel tank, fired each one separately - perfect patterns! have reset mixture down slightly on airflow meter and runs OK.
Hope the plug thing is all, but will stick to single electrode in future rather than bothering with triples! these had only been in for 400 miles.....
Have some photos of my rather dangerous looking injector test rig
and a few months after when the topic of plugs was raised, we were told they have been bought out by Beru and the French brand name is no longer used which might be because they had as much trouble spelling it as the rest of us.