I had the same problem and it was the coil not supplying enough voltage to the system. Bad wires will do the same. Wait till dark. Let your eyes get accustomed to it then start your engine and check to see if there is any arcing out of the wires somewhere either on the engine or the fuel pump ot other wires nearby. If so, change them with a good heavy duty wire. I use MSD. They cost more but worth it. Also had cracked caps cause problems. Sometimes you can't see the crack. Look for carbon tracing inside the cap. It is definately ignition problems. You could also have a bad wire to the coil supplying the 12 volts to it. If you have a balast resistor in circuit, remove it. You don't need it on HEI. Do you have an HEI coil? A stock one won't be enough to power it properly. MSD coils are not expensive. Are you using a square style in the cap or a standard round type? Make sure it is an HEI coil! I hope this helps.
