Be sure it is grounded securely. On many distributers, the advance plate is grounded to the distributer body by a short piece of braid. On my TR4 this braid was connected to the plate with a rivet. Seemed to work well enough with the points, but with the PerTronix the tiny looseness of the rivet raised hob and the car kept cutting out. I can't remember now the alternative method I devised to ground the PerTronix, but it was simple. The ignition worked flawlessly thereafter.