Your advance curve is too slow, The 30 degrees should be in by 2800 RPM. (how often do you run it over that?) This will improve you mileage and drivability. Plugs sould have a little color, not white, after a good run. Too lean will also kill your mileage and can lead to detonation. Use a vacuum gauge while your driving ^^^ to see if you are using too much throttle, plus it makes you feather the throttle to keep the needle at its highest....If your alignemnt is so far out it would be wearing the tires and squealing around turns.....

Some little things you might want to verify; is the speedometer/odometer calibration good. In your case if the odometer reading is "slow", that would make your mileage look worse. You mentioned you were using a "stock AFB", assuming it is a '57 carburetor, you might want to check the float levels and the power pistons; they shouldn't stick in their bores. (I mention this, some people put a new carburetor on and most "replacement" units are rich to begin with). Which brings up another point; reading the spark plugs. I don't claim to be any kind of an expert on this, I almost always have to refer to illustrations. Find colored pics to reference to. Ted Eaton, John Mummert and others can give advice on plug reading. Not knowing your driving habits, this is another factor. Mileage is a really tough thing to improve on, I think it's easier to go faster than to improve the M.P.G.

PF, I don't think it smells very rich at all when idling. The pipes have slowly accumulated a light film of black soot, but it does not seem excessive to me. I have verified that the jets are what was factory-specified, so they should be pretty darned close to where they need to be.

Ted, yes, I have. The mechanisms are both working properly. I have not adjusted either one. The advance can is a replacement, but it's the kind with the spring and shims and spacer, and I just swapped the internals directly from old to new.

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

Have you checked that both the mechanical and vacuum advance ignition curves are working independently of each other with a timing light?

Lorena, Texas (South of Waco)

Not a definitive method, but what do your tail pipes look like after a good run & does it smell rich when idling? Maybe that carb is jetted way off?

Paul

I have now run a tank full with clean air bleeds and attained a breathtaking 12.5 mpg. The plugs continue to look clean, possibly slightly cleaner than they were with the dirty bleeds. That suggests to me that the air filter is probably OK but I think I will go ahead and replace it.

It must be the alignment and the 225-width tires that are killing the mileage. My upper control arm bushings are gone, so there is noticeable negative camber, and though I haven't tried to measure toe, I know there is a big dead spot on-center in the steering and I am pretty much continually making small corrections to cruise in a straight line.

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

Re Popular Mechanics...

ESTIMATED AVERAGE ANNUAL GASOLINE BILL: $185 for 10,000 miles.

Oh, those were the days...


South Australia

Also, thought ya'll might find this article interesting. http://books.google.com/books?id=RuEDAAAAMBAJ&pg=PA109&dq=popular+mechanics+engineer+1957+ford+plymouth&hl=en&sa=X&ei=mBJSUpmCOe634AOap4HABg&ved=0CD8Q6AEwAQ#v=onepage&q=popular%20mechanics%20engineer%201957%20ford%20plymouth&f=false

It's an old Popular Mechanics comparison of the 1957 low-price three, Ford, Chevy, and Plymouth, with some performance data including fuel economy.

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

I really like this idea of running manifold and ported vacuum lines to gauges inside the car, at least for the purpose of doing this tuning. Thanks for that suggestion.

I have been scouring the internet for any definitive statements about advance maximums, specifically in cruise scenarios, and have not been able to find anything. It seems as though nearly every stockish engine wants 32-40* of total mechanical advance by 3500 rpm, around 10* initial, and an additional 10-15* of vacuum available on top of that. I have not found a single article making reference to what the curve does between its beginning and ending point. When does spring number 2 optimally come into play? At what rpm and advance value? Of course there is not a blanket answer to those questions, but I think it strange that I have not found any references to them at all. The mechanical advance "curve" is really two straight lines, after all: one based solely on the first spring, and a second, shallower-angled line based on the 2 springs working together.

The best procedure I read for mech. curve tuning involved selecting an rpm, flooring the engine just below that rpm and on through it, listening for spark knock. If none, advance the distributor 2 degrees and repeat. If knocking, retard 2 degrees and repeat. In this fashion, the maximum advance the engine can handle at each selected rpm can be determined and recorded. The curve the engine wants can be plotted. Then, the tuner can start playing with springs and initial advance and maximum limiting to try to reproduce that curve. After that, the vacuum advance can be tested in a similarly methodical fashion. If I was watching manifold and ported vacuum gauge readings while driving, I should be able to determine an ideal curve that maximizes both vacuum readings during cruising.

Sure, it'll be tedious, but this will be the next step for me.

In case anyone's curious, my current advance characteristics are as follows:

initial: 8*

Crank advance at crank rpm:

500 - 0*
600 - 3*
700 - 6*
800 - 8*
900 - 8*
1000 - 10*
1250 - 16*
1500 - 17*
2000 - 18*
2500 - 21*
3000 - 22*
4500 - 30* (max, I think)

Crank advance at "Hg vacuum:

5" - 8*

10" - 26*

12" - 30* (maximum)

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

As Doug mentions, I do have two vacuum gauges mounted in my ’55. While I don’t recall the various numbers, peak fuel mileage occurs where both gauges are reading at their highest. Here’s the link to the picture of the gauges in a previously posted thread.

Vacuum gauges for both manifold and distributor readings

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While an adjustable vacuum pod on the distributor is the easy method for altering the amount of advance being supplied by the vacuum signal, these are getting increasingly more difficult to get for the older Ford distributors. Modifying the distributor with a differently staged ported vacuum hole at the carburetor is another option but those new ports take a bit of thought and experience to correctly place that new hole in the carb bore.

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Here are some past threads regarding vacuum to the distributor.

Demon carb ignition timing requirements

Demon carb vacuum advance signal

Ported versus direct vacuum – Pros and Cons of each

Lorena, Texas (South of Waco)