Slant Six 225

Brandon. Yes, common problem in slants w/ the Holley 1920 carburetor. I dealt with exactly that for decades in my 1969 Dart. Mechanics did valve jobs, swapped intakes (vacuum leak?), finally a whole new long block gave the same issue. A 4th Holley 1920 made it idle like a dream. Rebuilt ones are usually no good, though my last one was. Maybe try a later Holley 1945 or even a fuel injection system like a few slant guys have (and I hope to).