This is just a tad bit premature, because I've not fueled up this week, but I've just crossed 218 miles on my current tank as my fuel tank has just reached the top of the white "Reserve" section. I'm probably down to one to two gallons now... and have used around nine gallons of fuel.

My odometer has at least a 1.05 error ratio putting my true mileage about 229 miles. If I put only about 9 gallons into my car tomorrow morning, that kicks my fuel economy up to 25 MPG!

Considering I could not break over 16 mpg for the last year - that is a huge jump into "normal" territory.

What has changed?
I replaced my throttle shafts, jets, and "riveted" my butterfly plates closed (hot brass rivets nicely). I do not think this made any real difference as I had tried this approach before. Plus the jets are at right about 12 flats and the throttle will not adjust down under 1600 rpms... This should be a recipe for bad economy, but the opposite has happened.

What I think changed is this...

I replaced the old 1968, self-adjusting rear brake drums with manually-adjusted 1967 drums. The shoes in the old drums were worn to almost nothing and a lot of dust came out of the drums when I removed them. I think the self adjusting setup was ratcheting up the shoes causing the rear of the car to drag. I could not "feel" the drag, but I think that shoes worn away within 1 year is the proof that this may have been the *real* problem.

I'll post after I fuel up and provide a real calculation.