Difficult cold start
I have a 73 Duster with the slant six & looks to be un-modified at all. Sometimes it will sit outside for months without starting it. (it's not road worthy) I just tap the throttle pedal to set the choke, crank it for a split second, crank it again & it always fires right up. Too much fuel on starting (one full pump) & it is hard starting. Try just tapping the gas pedal first to set the choke (confirm that it's working) & see if that works.