Good luck. I went thru 4 Holley 1920's in my 69 Dart 225 over several decades before I found one that made it idle smooth. All the others (parts stores) ran lean at idle, wanting to stall when leaving a stoplight. Several mechanics looked at it, to no avail, though twice they said "valves" and rebuilt the head. After a whole new long block ran the same, I decided it must be the carb, and it was. Many bad rebuilt 1920's in the parts chain. One to consider is the "Holley Economaster" from late 70-80's, for better mileage. I think I have seen a new one for the slant on ebay (~$150).