"There is no such thing as an IMCO or NON-IMCO carburetor on the '68 Mustang with a 6cyl."
An earlier 1966 Autolite 1100 1v carb and distributor is NON-IMCO.
A '68-'69 later Autolite 1100 1 carb is an IMCO carb.
....What part of this do you not get?
The part I don't get is where being testy enhances the logic of your argument, or contributes anything to the discussion
By that definition a flathead stromberg is NON-IMCO as is a brand new Holley 600 CFM...in that case the list of the NON-IMCO carburetors is endless.
Apart from this back and forth the 'facts' remain that the 'mechanically same' YF Carter was used on IMCO as it was on Thermactor (the two choices for emissions standards for all Ford cars at the time, with the possible exception of Cali cars).
The Facts as I understand them, from both research and experience:
The 'only' difference in the YF or Autolite 1100 (less SCV) with IMCO would have been plastic (removable) limiter caps on the mixture screws...'removable' (most of which have not survived to date)...the 'only' other difference was in 'calibration' (adjustable).
There is no other mechanical difference between the Carter YF or '68 Autolite 1100 for Thermactor vs. IMCO (the only two factory choices one would have on the OP's car).
There are no vacuum connections on the 'carb' that operate the 'spark retard system' which is the crux of the IMCO ignition design.
The true 'improvements
' were not exclusive to IMCO, that is the head castings were not different on IMCO vs. Thermactor...the exhausts were as I have noted.
The IMCO ignition system is primarily based on the 'spark retard' distributor cannister, which as I have noted can be negated by plugging the vacuum connections noted above. At that point the '68 distributor is comparable to a standard vacuum/mechanical advance dizzy.
The other parts of IMCO which included 'slightly' different carb calibration 'from Thermactor', a hotter thermostat, etc. are all essentially efficiency improvements not specific to the 'spark retard' ignition system of IMCO.
There is far too much evidence out there by people who have these carbs, both the 'NON-SCV' Autolite 1100 and the Carter YF, for anyone to simply dismiss them as 'junk' (in particular the Carter YF). That is a minority opinion and you are welcome to it, but to throw 'the baby out with the bath water' is just that.
If you were unsuccessful at getting the IMCO system to peform well, I would not be surprised (Ford had relatively the same lack of success). It was a relatively short lived 'system' (especially in terms of ignition) that gave way to the characteristics of Thermactor (air/smog pump) and later EGR. Again, I've given a very simple method that most use to by pass the IMCO 'spark retard' system. If you were not able to get the Carter YF to peform very well...that is another story, isn't it? However to dismiss the YF out of hand and portray it as an IMCO 'specific carb' is a misrepresentation, not just a matter of opinion.
Though I may not have been on this forum long...I am no newbie to these engines or these emission systems