Fuel Economy..?

I kept careful records in my 69 Dart 225 for years. Averaged 21.5 mpg hwy. That was mostly back in the 55 mph speed limit days. The last 3 years I had it, I had a Crane XR700 electronic ignition, but don't recall the mileage improving noticeably. The Holley 1920 always idled lean, not sure about higher rpm but the plugs were always light grey.

Maybe the best addition for tuning would be an oxygen sensor monitor. Wideband are best, but expensive. I got a few simple lean/rich indicators (MSD or Holley) on ebay for ~$25 (list ~$175). Even cheaper, I got some surplus kits intended for Onan generators, which includes sensor, bung, wires, indicator box. Only problem is ~30 sec filter makes it hard to tell cause/effect when I adjusted my Holley Pro-jection. Not much an issue for monitoring a carburetor in steady driving. You could even jet the carb slightly rich and plumb a vacuum line to the cabin w/ a little valve to lean it out per the O2 sensor. One company planned to sell that approach (automated feedback) back in the 1990's.