1980 ford with cat failed the test as follows:

Driving test:
HC ppm (maximum allowable/my reading) 199/178
CO % 1.3/.47

Idle test:
HC ppm 355/485 *** fail
CO % 4.03/2.08

There seems to be a slight misfire when idling but not noticable while
driving. All new plug wires, rotor, cap, plugs.

Could an adjustment to the idle mixture screws reduce the HC to passable
levels?

HC is high in both idle and driving test. How is this significant?

Thanks