If there is no resistor or resistive wire, then the coil may be burnt internally due to 12V going to it at all times. As an engine heats up to operating temperature, it needs less primary voltage to run, hence, a resistor or resistive wire is inserted to lower the voltage, thereby, reducing the amount of current going through the point set and burning them up.
So, a swap out of coil may be needed,
Another place to look is point resistance, may have to take a file across points contacts to remove the carbon build-up. Usually want less than one ohm resistance across a set of closed points.
Ever think of changing to Petronix ignition?