Back in the days when Holley was producing thousands, perhaps tens of thousands carburetors for production vehicles they used a restriction in the upwell and even at the top for certain situations. Keeping the fuel jets completely submerged is generally better for predictible fluid flow and more so in engines where pressure differences at idle are unsteady. Hot rods and race engines often have unsteady manifold vacuum at idle.
"Submerged metering passages are free from instability and irregularity of discharge when the head is very small".
[URL]https://www.tapatalk.com/groups/racingfuelsystems/relocating-the-holley-idle-jet-t18.html[/URL]
Link to NACA TR-49 in this post by Mark Whitener
[URL]https://www.tapatalk.com/groups/racingfuelsystems/viewtopic.php?p=12472#p12472[/URL]
More in-depth about how e-bleeds work in this discussion
[URL]https://www.tapatalk.com/group...ar-booster-inserts-qft--t1831-s10.html#p18192[/URL]
and in this archived discussion with Shrinker from the old Innovate Forum
[URL]https://www.tapatalk.com/group...tml?sid=b55fc94997078585ea3a3b3d5a04750f#p982[/URL]