Warning, be very carefull about doing mods like this....

There are many ways to solve those lean or rich idle issues.

#1 Timing must be set correctly. Not by the book specs either. Timing is set by your specific engine conditions.

#2 The throttle plate position is extreamly important. If they are set up wrong, it will make you think you need an IFR adjustment, then once it is done, your really in trouble.

#3 Most folks never set the rear throttle plates correctly either. Those are also very crittical to getting a good idle.

This is not a Willy-Nilly adjustment. This is the last resort fix once all other options have been tried. Only someone that really knows carburators and engine tuning well can detemine if this is a fix that will solve your issues.

Looking at the transition slots at the bottom of the carb... If that little square in this photo ( the center-rear of the bore) is anything but a little square, then your throttle plates are not set correctly. Front and Rear must look like this.

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66 Stang 385+ HP 306 .494 /.520 225 durr @.05, 200cc Windsor Sr's, Edle RPM, C4, 3.00 posi, 575 Annular Mighty Demon, 22 MPG,