[Tom Vaught]

Tuning the Transfer Slot in Holley Engineering.

The Transfer Slot (many times made by a EDM process) is typically in the range of .190" tall by .025" wide.
You have a general TS location and then the Slot is raised .020" and then lowered .020" on different carbs to find the "Sweet Spot" for that specific Throttle Bore/Throttle Plate diameter.
The "Early" and "Middle" sections of the "Off-Idle" Fuel/Air curves are primarily affected by these changes.
(The Idle Mixture Screws are always adjusted for each change to allow consistent Data Change comparisons.)

The Idle Feed Restriction (Idle Jet) is varied +/- .002" but the Idle Air Bleed Holes (Restrictions) are not changed when the IFRs are changed.

A Change in the flow curve initiated by the large IFR suggests that driveability would be improved, BUT that assumption could be wrong in actual testing and the drive modes could be poorer in modes below 30 mph. There is always a "give or take" in calibration tuning.

Changing the Idle Air Bleed (-.005" and then +.005") without changing the IFR may not significantly affect the Idle Set Point but the drive modes below 30 mph will be affected. Again there is a balance in what is acceptable.
"Balancing" the IFR and the Idle Air Bleed takes time but is worth the effort. The Idle Mixture Screw may have to be adjusted slightly to get back to the original Idle RPM Set Point.

Changing the Idle Air Bleeds upward, at times does improve the overall drive and Power modes of the carb. Cliff Ruggles found this out on his Holley 4781--2 carb when he increased the Idle Air Bleed size slightly and the overall performance was better.

That carb later went on the Engine Dyno and the Dyno people told him to "never touch that carb, it was perfect".

More info Tomorrow.

Tom V.