46yblock,  you're right, those are both valid possibilities, and the sort of thing that I can never know for sure.  The best I have to go on is that the shape of the screws matches that of the drawings in the shop manual.  But that doesn't necessarily mean anything.

I'm about ready to take it as is and just do the best I can with what I CAN tell.

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

Maybe someone in the last 50 years overtightened the idle screws, enlarging their ports/seats.  My 2100 requires 2 1/2 turns out.  First tried 1 1/2 and no way.  Works good though.  Like you said, whatever works.

Another possibility is that a different set of needles were used than original, with a different profile. 

Mike, located in the Siskiyou mountains, Southern, OR 292 powered 1946 Ford 1/2 ton, '62 Mercury Meteor, '55 Country Squire (parting out), '64 Falcon, '54 Ford 600 tractor.

I think you're right, the holes were just on the earliest 2100s. I wonder if the relative position of the advnce pickup is different too.

Well, I installed the carb with no change.  I just can't find anything wrong with it.  It doesn't look like the mixture screws, nozzle bar, or throttle plates have ever been replaced; the serial number is correct for the year and application.  I don't know how it could be happy 5/8 turns out from seated mixture screws when all sources indicate they should be 1 turn or more, but it's very happy there, very smooth and nice.  And the engine picks up speed and is smooth with the vac advance disconnected, even though the vac advance is adjusted to spec.

I'm fine with accepting the idea that the ideal settings on my car are other than Ford's specifications, but I just want to understand WHY that is the case. 

I know that my engine has '56 272 heads rather than '59 292 heads, which means smaller valves.  I have no idea what cam is in it, but it's obviously not high-performance.  Yet I would not expect either of these things to account for the deviation from spec.

But I have the feeling that I will never know the WHY to this and am better off trying to forget about it and just find what seems to work.  Meh.

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

I was looking at my 66 Mustang manual which also has the 2100 carb but I guess there is a slot in the later ones as opossed to holes.

  

Oldcarmark, I think I have both carb AND timing problems, but I thought I would start a separate thread for the carb stuff and deal with it first.

You describe a transition slot.  The 1959 2100 doesn't have a slot, but 2 holes, and the advance port is between the two in height.  But if it is normal for the bottom of the slot to be exposed to manifold vacuum, then it is probably also normal for the bottom of the lowermost hole to be exposed as well.  The manual says that these transition holes are to act as air bleeds at idle, in addition to the 4 total idle air bleeds in the nozzle bar assembly. 

I looked around as best I could for any cracks in the carb body where fuel was, but found none.  What's more, the gasket that I thought I had destroyed appears to have been two gaskets glued together, for it came apart in two clean matching pieces.  I reinstalled the power valve using one half, put the carb on and ran it again.  This time, there was no fuel in the power valve cover AND the gasket looked dry.  It's hard to be certain, but I think any leakage there has been eliminated.  Yet there was no change in engine behavior.  The only other thing I could think of would be clogged air bleeds, resulting in the need for the throttle plates to be more open and the mixture screws more closed to obtain a good fuel/air ratio.  I went back through all the idle passages with water so I could see the streams flowing from the holes, then dried them with compressed air.  I still need to install and test, but I know that no passages in the idle circuit are clogged.

If I seat the mixture screws the motor will die.  It will die if I take the screws within a quarter turn of seating.  It will run 1-1 1/2 turns out, but it is rich and you can see the exhaust vapors out the tailpipe.  At this point, if I reinstall and there is no change,  I see no choice but accept things as they are, or replace the carb.  I am certain the fuel level is right.  There just aren't any other variables.

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

The transition slot should be like a little square UNDER the throttle plate-about .020-.040 showing.The only way to determine this is take the carb off and set it prior to reinstalling.Count how many turns of the speed screw it takes after it touches the lever on the throttle plate to expose this amount of slot so you can reset it without taking the carb off again.Write it down somewhere.That setting never changes.You want to be as close as possible to that setting.As more of the slot is exposed more fuel is drawn out negating the mixture screw adjustment.You will never get a proper idle with excessive transition slot exposed.Initial setting on the mixture screw is 1-1 1/2 out from closed.If you start the mo=tor and LIGHTLY close both screws the engine should die.If it does not you have fuel from somewhere else feeding the motor.The only circuit which is supposed to be active at idle is the idle circuit controlled by the mixture screws.I really think you have a carb problem.Maybe an internal crack in the casting feeding the power valve feeding into the motor. at idle.To set the idle speed you bshould not need to turn the screw much more than 1/2 turn at most.You can play with the timing all you want BUT you have a carb problem not timing.(in my opinion).

  

I have just spent some time with my carburetor ensuring that the throttle plates seat fully beyond the 2 idle transition holes and the vacuum advance pickup hole.

After messing with it, the very best running conditions I could get at 575 rpm in park were as follows:

- dist. at indicated 10* initial advance

- Idle speed screw 5/3 turns in from just touching tab on throttle shaft, throttle plates lightly seated

- Mixture screws each 5/8 turn out from lightly seated. 

This setup yields a steady 575 rpm and a touch over 21"hg vacuum.  Yet 5/3 turns has the throttle plates far enough open that the lowermost idle transition hole is fully exposed to manifold vacuum, as is the bottom edge of the advance port.  Turning the mixture screws in or out even just 1/4 turn from the best position results in an obvious decline in idle quality.

I checked the power valve chamber for gas 3 times.  The first time, even with a brand new valve and gasket, there was some fuel in it.  I inspected the gasket, the valve, and the gasket seat and found no flaws, so I put it back together and over-tightened the power valve, which caused the gasket to shear halfway through its thickness.  I installed it anyway and checked it twice.  Both times the gasket was visibly wet but there was no gas collected in the cover as before.

Do you agree that 575 rpm should occur with less throttle and more mixture screw, indicating a problem?

As ever, thanks for patience with my long posts and for your wisdom.

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