I am restoring a 73 challenger with a 340 engine and 6-pak carburation. I have replaced the voltage regulator, the ECU and have the proper gap for the distributor reluctor. The plugs and plug wires and the resistor are new. When cranking all of the cylinders appear to fire, (individual header pipes get warm), and when I let off of the starter, it dies. When the starter is cranking, there is about 9.5 volts to the coil. At times it will backfire up the center carburator. If you ever want to see the neighbors kids eyes get really big, let them see that! Any ideas and thanks much!