[Tom Vaught]

Well Vic, glad to see you back again.

1) For many years Holley had a 2 circuit idle system on the front of the carb and a very tiny fuel purge circuit on the secondary side of the carb. This helped the carb from gumming up on the secondary side. Barely worked but it was there for a reason.

2) Then about the mid 70s, some people decided that they could do a better job of keeping fresh gas in the secondary side of the carb bowls by adding a secondary idle system THAT YOU COULD ADJUST. MORE OF A MARKETING DEAL VS ANYTHING ELSE.
The open plenum and divided intake manifolds still worked fine with the 2 corner idle system. Dual metering blocks vs a metering plate where you could screw with the settings externally and really foul things up.

3) The Primary Idle Screws were set to 1.5 turns out from seated.
BUT the Secondary "Stale Fuel Purge Circuits" on the secondary side were fixed.

3) Now with the change to a 4 corner idle carb set-up you gave the guy twice as many things to screw up on that circuit.
Then later the Idle EZE carbs allowed you to close the rear carb throttle blade back to almost touching the bores but then
people thought you needed to do the same with the primary circuit so the Primary Circuit got all screwed up.

4) Today most people understand the requirement to put the Primary Blades in the right location on the Primary side of the carb.

5) Along the way the BIG 455 and 454 engines got small when the big 535 and 600+ cid engines replaced the "Small Stuff".
So again you need more idle airflow and that means larger blade openings for the 4 carb barrels.
Drilling holes in the carb blades only works for a given range of carb size.

6) Don't assume that every carb must have the front of the carb and the back of the carb exactly the same for the carb to perform properly during idle and off-idle, as well as at WOT.

7) Historically, unless you have a really big engine you do not need a lot of airflow from the carb to maintain a proper idle. Some of this Idle Eze stuff was just a copy of the Carter AFB carbs with the Idle Air By-Pass system Screw and drillings. But any way you can sell carbs, the marketing guys will say you need that stuff.

Hope this helps.

Tom V.