There was a fella on Moparts some time back that did a rebuilt 318 w/KB zero deck Hyperutecic's (sp?) with a OD-833. He last reported 36 MPG's.
While I'm sure it wasn't a tire frier, this mileage experiment was a good one. He also left a few mods on the table. He had more in it.
And YES! Like said right above, carb float has an impact.
Amazing!