Miles per gallon?

Dodge72 said

I personally get 17 mixed MPG with a two barrel carb and 3.23 gears on my slant. With a one barrel carb and I assume stock gears you ought to be getting a lot higher than 10-11. Have you done a tune up recently? Valve lash set? Is the carburetor mixture set properly? Maybe timing is off? Lotsa little things can help or hurt.

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Well, we thought that it was being caused by a bad thermostat. The car was never getting any warmer than slightly above the "C." After replacing the thermostat, the car gets much warmer and operates at a reasonable temperature (as a bonus, I am not freezing as I drive.). Here is the breakdown in case my calculations are off: 23217 at top off #1, drive for a few days and re-fill at 23343. 23353-23217=136. I put in 10.5 gallons, 136/10.5=12.95. (I did just notice I was a few miles off in my calculations earlier, but 12.95 still seems low.) I took a picture of the odometer at each fill so I know that to be accurate.

My father is a mechanic by trade and says the carb appears to be in tune, not to mention the fact the car flawlessly. It has pretty old tires on it, but I can't think of what else could be causing such poor fuel economy.

Also, that is the third top-off/calculation I have done. The other two came out at 10.5 and 11.2 mpg.

Aside from a carb-tuning and valve lashing (which I am not all that familiar with, but I do know the cars run poorly when they need it.)

What else could be causing this?