I've got a '71 with a 250/4 speed (granny low) that has an HEI dizzy. I have issues with a stumble off idle and when under a load at cruising speeds 55-60 mph (climbing a hill). I have been fooling around with the timing and the air/fuel mixture and it is a little better and a little worse.
the stumble is less severe but now the idle is so high I can't adjust it any lower. I set the timing on 4° at idle with the vacuum advance disconnected and I ran the mixture screw all the way in then 2.5 turns out. Then I turned the mixture screw out until I reached max vacuum. At this point the idle rpm is about 1200-1500 and the idle adjustment screw won’t reduce the rpm anymore. I’m lost with this configuration; I’m thinking I need to get back to a baseline but how? Anyone have advice?