Hi Martin, Just thought i would share my similar experience. Car starts and ran fine until 10 minuits up road and squeezing the loud pedal a bit hard i found at about a constant 80mph it did a sudden ignition cut for a mere second , i would back off and the car would seem fine. Had a long french trip looming so changed plugs and cleaned jets.To try and sort. Car then repeated the same problem , so a trip to Peter Baldwin at Wilshers Garage Royston revealed the same issue on rollers. We stripped off the Dizzy cap (Aldon Ignitor) and found loads of carbon type dust in there,gave it a thorough wash out , it apparently causes tracking at high revs. Replaced everything and all is fine now 2000 miles later. I also had a problem when blipping throttle at low revs engine trying to cut, all it was i found the spark plug gaps were worn way too big (about 1mm)causing week spark New plugs gapped sorted this out ,and i can now sit and blip throttle Hope this is of some help. Richard.