Now that my Fairlane is finally running reliably, I have been driving it to and from work all week. The drive is a mixed bag with most of the miles being lightly hilly country roads at 50-60 mph, with some city/stop and go at one end, a brief stretch at 65-70 and a couple of lights in between. It's about 34 miles one way. I have averaged 11.8 MPG on that route, which seems several points low based on what I've read here and what my 292-equipped '59 Galaxie used to do (15-18).

Mechanically, compression is good, engine is stock 312 with stock cam (believed original to car with 85k miles). Timing chain is new, carburetor is stock Carter AFB, trans is FOM, 3.10 rear axle. Distributor is original, vacuum advance is new with old internals swapped in (though they could easily have been changed since the factory), 10* initial timing. I have been using regular gas (e10, really, as that's all that's sold here) because there hasn't been any spark knock so why pay for premium?

I'm pretty sure I don't have any brake dragging but I will check it tomorrow. Also, the front end is worn out so the alignment could be adversely affecting mileage to some degree. I have pulled and checked different spark plugs at various times and they all look clean with some darkish brown color on one side of the insulator and a pink tint on the rest of the insulator.

I have a '57 Autolite 4100 in need of some repair and a rebuild kit. Do you think that the 4100 would give significantly different mileage than the AFB, if set up with stock jetting?

Based on what I've said, would time be better spent playing with carbs or recurving the distributor?

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

Based on what you've said, I'd start looking at the front suspension. As you mentioned, misalignment is a potential mileage killer. Toe in (or out), if out of spec. will cause a lot of drag. Also, ethanol blended fuels will diminish economy. If your AFB is sound and dialed in correctly, I doubt switching to a 4100 will make a significant improvement. I have been reading about recurving the distributor for E10 and there may be some help there but I think it will relatively minor. To go from your present 11.8 to 15.0 is nearly 30%. That seems like a tall order to me.

I believe I found a big chunk of the problem. Somehow there was a residue of some kind clogging the main air bleeds. I have noticed this happen before, it seems like gasoline bubbles up the air bleed and dries leaving a film across the tiny opening. I hope it is because of all of the idling I did when trying to sort out ignition trouble and won't be a common occurrence. I'll monitor it. Anyway, we'll see how much difference it makes.

I also mapped my advance curve, it appears to be pretty close to the manual's specifications, except a bit more aggressive. The vacuum advance is definitely too much, so I will have to step it back a bit. One change at a time though.

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

I did my first stint of driving today with the air bleeds nice and clear. It's too early to tell whether fuel consumption has changed, but one thing's for sure: the engine is running hotter. The needle sits near the upper end of the "normal" band on the gauge, whereas it has been in the center all week.

I'm guessing the leaner mixture is just burning hotter. I suspect that is an indication of the need to recurve the distributor as well. I did the math, my vacuum advance is adding 30 degrees of advance at 12" of vacuum, and I'm sure the engine is well above 12" of vacuum during 95% of the time it's running. At 2000 rpm my mechanical advance (including initial) is about 24* so that means at 50 mph and above while cruising I have at least 54* advance at the crank :-O

What's strange to me is I never hear any spark knock. I thought you could give an engine as much advance as it could take without spark knocking?

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

It does sound like you have some tuning to do. 24 degrees at 2000 rpm means that the mechanical advance is coming in very quickly. Either aftermarket springs have already been installed or perhaps one or both of the original springs is missing or broken.

I didn't see the part about 24 degrees being initial + mechanical when I originally read it, so it may not be coming in too quickly. What is your initial?

For now, disconnect and plug the vacuum advance and focus on the mechanical. When the mechanical is where you want it, work on the vacuum.
Concerning the vacuum advance, you can use a length of hose and a standard diagnostic vacuum gauge to see where the vacuum is when driving so that you are not making any assumptions.


Lawrenceville, GA

The Vacuum advance and centrifugal advance are supposed to add up. Remember at part throttle, that is to say high manifold vacuum, you do not have the cylinder "packed full" of air/fuel mix so the pressure is much reduced and combustion is slower. The total advance is intended to compensate for this. If you don't hear pre ignition knock or ping it is probably OK and you wont hurt it. I seem to remember Ted saying he has vacuum gauges on his driver's manifold and advance mechanism. Maybe he could confirm a typical reading at the vacuum advance diaphragm at reasonable road speed and load.

The higher temp is interesting. What do the plugs look like after some highway driving?

Doug T

The Highlands, Louisville, Ky.

HAve you got a vacuum gauge, If not get one it will be you best friend..



"Came too close to dying to stop living now!"

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)

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

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