having startup issue

im having a issue after driving my 74 duster /6 , if i shut it off and try to restart there is no spark but engine will crank.... ive swaped parts from my 74 scamp as it has same parts.. ive swaped ignition box, voltage regulator, coil. and replaced balast resistor.. what else is there im missing anyone can help please and thank you

matt
IEduster