my '78 w/turbo motor has a miss that goes away as rpm's rise. the distributor has been "welded" to suit the Accel DFI. it also has a HI-6 Crane ignition with a mallory coil. Everything is new( motor,DFI, ignition, fuel system, etc) except the distributor, whichhas been swapped with 3 other units. What could be causing the miss??