Well guys, I finally found the "source" of the problem.
Like I've told you guys, the engine mounts are new, so is the transmission mount. 
Well, since apparently the engine itself checked out, and the Isky E-4 really provides a something rouger idle than stock, I started looking at other sources of vibration. The exhaust on the car is relatively new, and it's dual, with a H pipe. From the factory the Galaxie had only one exhaust pipe, and there was the problem. On the right side of the car, the side still with the factory rubber mounts, one of them was so hard that almost felt like plastic. Replaced that one, and the one near the tail pipe exit and the vibration on the floor pans disappeared like magic. 
That made me worried about the 41 years old body mounts...
The car is not showing signs of having bad body mounts, and from the underside they do look good. Just as a precaution I started looking for a set of body mounts, and NOBODY reproduces those for a '66 Galaxie, that is what my '74 is. 
If someone would, they would have a huge market here in Brazil, as all our Galaxies are versions of the 1966 model. 

Túlio Lazzaroni "FORD", Florianópolis SC Brasil.

'74 Ford Galaxie 500 292 V8

'82 Ford Galaxie Landau 302 V8

'98 Chevrolet S10 4.3 V6

'01 Ford Focus 1.8 Zetec

That's probably about right.  The E4 is pretty popular.  Maybe someone who has one can confirm.



Lawrenceville, GA

Well gentlemen, I took a reading on the vacuum.
Took the car to the local Ford dealer, where the chief mechanic is a close friend and used their vacuometer.
The engine was at operation temperature, idling at 750 RPM and the reading was between 13,5  and 14 inches (the scale is not that precise between a full inch reading and the needle oscillates about a millimeter, what I think is normal).
I was kind of expecting that, since all spark plugs read really good, the points are new, there is no excessive blow by, no popping on the carburetor, and the engine pulls really well.
The vibration is more of the harmonic kind, as it comes and goes in regular intervals. I'm starting to think it's the exhaust...


Túlio Lazzaroni "FORD", Florianópolis SC Brasil.

'74 Ford Galaxie 500 292 V8

'82 Ford Galaxie Landau 302 V8

'98 Chevrolet S10 4.3 V6

'01 Ford Focus 1.8 Zetec

It is not a stock cam. I will not idle like a stock cam. A vibration could be an exhaust system thing.

Thanks Charlie.

After hearing from NoShortcuts Charlie I realized it's a damper.
Believe you or not, people here calls mine kind of springs a "dual". Not to be amazed, as people here call every single four barrel carburetor a "quadrijet" and a two barrel a "bijet"...

Well, will borrow a vacuum tester, and do some readings as soon as possible.


Túlio Lazzaroni "FORD", Florianópolis SC Brasil.

'74 Ford Galaxie 500 292 V8

'82 Ford Galaxie Landau 302 V8

'98 Chevrolet S10 4.3 V6

'01 Ford Focus 1.8 Zetec

That is a damper, not an  inner spring.  The vacuum gauge will tell you more.



Lawrenceville, GA

Maybe a harmonic from the muffler change? I've had cars that needed resonators added, but at cruise, not idle. The comment about feeling it in the floor pan is what prompts this.


miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

Here are the valve springs. Just pulled a valve cover and took a picture:




Túlio Lazzaroni "FORD", Florianópolis SC Brasil.

'74 Ford Galaxie 500 292 V8

'82 Ford Galaxie Landau 302 V8

'98 Chevrolet S10 4.3 V6

'01 Ford Focus 1.8 Zetec

Charley, great to hear from you too!!
Maybe I was mistaken, my "inner" spring is the flat kind. Not really a second spring. Around here they are called double springs, and the other triple.
I have to get a vacuum reader borrowed with someone. Then I can tell what it reads.
When I rebuilt the engine, all work was done by me and a friend that owns a shop, and we measured it. It was solid as a rock. But again it was back in 2010, and I don't recall the actual reading.


Túlio Lazzaroni "FORD", Florianópolis SC Brasil.

'74 Ford Galaxie 500 292 V8

'82 Ford Galaxie Landau 302 V8

'98 Chevrolet S10 4.3 V6

'01 Ford Focus 1.8 Zetec

Comments, Tulio.
1) Like Rono, I'm surprised that you're running dual valve springs unless you're counting a damper coil as an actual spring.  No, a second spring would not be responsible for a change in the idle quality.  It's an unrelated thought.  I'm just thinking in terms of your usual rpm operating range for street and highway use and valve train wear and tear factors.
2) I'm with Charlie in trying to get a handle on your idle quality concern.  What kind of a vacuum gauge reading are you getting at idle?  In addition to the gauge reading number, is it a steady reading, or rapidly twitching (pulsing), or slowly fluctuating ('walking')?

GooD to hear from you.  It's been awhile.  Glad that you got that 4100 carb working okay! 

Regards,


NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York