My Holley 600 with vac secs. did this on several occasions over the years. It was always some small speck of trash in the needle and seat. Cleaning that out with carb cleaner always fixed it. Try that and see if it doesn't work.
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'66 Coupe, 306, 350-375 HP, C-4, 13.07 e.t., 104.8 mph, 1/4 mi.
O.B.C. #2
'66 coupe
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