vacuum leak or idle circuit in carb
[ autolite 4100 has Four Corner Idle circuit if they are clean, and pulling
,the 4100 should should run with front two idle screws screwed softly all
the way in (but run ragged and choppy) (it's working) ..
Put your hand over the idling cab and see if it speeds up OR smoothes out !
IF so ya got vacuum leak somewhere..
also the FE manifolds distribute Fuel better with a carb spacer Or
the factory wedge spacer... the 4100 is a great carb
that can run with the air lid OFF . (get your carter to do that).
try to use the factory advance if you can.