So I'm sat here crying that I can't drive the Z to Goodwood tomorrow and park her in the "Special" car park! Been looking forward to doing that since starting the engine project! Reason why: since changing to the 123 ignition dizzy, the car has not been running smoothly at all. Like it's missing on a cylinder on a regular basis. And when I go WOT at 3k rpm she sometimes back fires albeit quietly. Unburnt fuel in exhaust is the obvious cause and you can smell it too. Same issue with vac advance both connected and disconnected. Timing set dead on 34 degrees all in at 3000rpm Changed back to old dizzy, same problem. Changed and gapped all plugs - no change. Changed all HT leads to no avail. Changed coil - just as bad. Checked low volt connectors, all is clean and tight. Took out each HT lead in turn while engine running at 2500 rpm to see which one had no effect but made no difference on the way the engine is running and she happily runs just as well / badly on 5 cyls. On the timing light it looks like every 10 or so sparks 1 or 2 go missing but while happening regularly, it's not consistently the same frequency of occurrence, if that makes sense. It does it on all leads. Anyone seen this behaviour before? I am utterly lost! Any thoughts most gratefully received. What I'm gutted about is just a week ago the car was running like a dream before I changed the dizzy. But changing the dizzy back again made no difference so I can't blame 123.