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It's a 4781 850 Holley. I was running a 2.5 power valve but it still does the same thing after I removed it and put in a block-off plug.
That`s because the pv has no influence on idle nor do the jets NORMALLY. Take it off and check t-slot location on the butterflies as it`s set up now, note where they are and report back. Could be lean too.............get a wideband a.s.a.p. and get a feel for the different circuits idle/transition can drive you  . 
72 Dart 470 n/a BB stroker street car `THUMPER`...Check me out on FB Dominic Thumper for videos and lots of carb pics......760-900-3895.....
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