After installing new distributors I decided to check all was well with each distributor by disconnecting the ignition control modules one by one. The car should run ok on just one coil but mine was running really rough when the furthest module/coil was operating alone. After a bit of fault finding I swapped the control module connection and found one control module was defective....so I thought
Edit...Problem was actually one lower lead not sat correctly due to the rubber insert in the plug socket being left on the plug!
Edit...Problem was actually one lower lead not sat correctly due to the rubber insert in the plug socket being left on the plug!