Well check this out!
After months away, I logged into RFS while finishing some coffee after lunch. Just going through the threads I had posted in at one time and....
Here's a picture of an IFR in the well. 4328 block from a 3 barrel
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This block also has emulsion tubes in the main well. The clue is the flat top main well plug and the air hole in the dog leg of the air well.
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apparently used on NASCAR 426 Hemi, L-88 and ZL-1.
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Tuner writes:
"The idle jet is in the well under the cup plug. The IJ in that location gives more rapid acceleration enrichment when the throttle is opened suddenly. "
So that confirms the purpose of this location is similar to the placement in secondary meter plates with the little horizontal connecting passage.
Related to Power Valve Tuning, these blocks have PVCRs around .093" dia.
Tuner writes:
"The PVCR size is affected by the emulsion tube in the main well. The lower end of the E-tube is just slightly above the PVCR orifice, you may be able to see it.
The PVCR is larger than similar size 1-9/16" venturi carbs which have no E-tube, such as 850 DP which come with .070", because the length and diameter (therefor surface area) of the tube adds friction and increases the restriction of the well, requiring larger metering area to result in same fuel flow as less metering area with no E-tube and less restriction in the well. "
Holley 950 3 Barrel