Drilling Holes In Carb Throttle Plate Blades

340inabbody said
Can someone here help me understand IF and HOW drilling carburetor throttle blades for an aggressive cam idle/T slot adjustment/optimization might also or not help in gear and out (park/neutral) idle balance on an automatic?

Background :
I have been having some issues of poor idle in gear and have been trying to tune (timing and carburetor) for a decent idle. I had initial success but now it no longer is working and the imbalance seems to have worsened. I now need like 1300 rpm out of gear to get 900 in gear. I have used two different carbs and getting ready to modify my 650 1450 throttle blades. My 750 doesn’t need the modification to maintain the correct idle T slot position. Bot both have poor in gear idle.
I have a wide band O2 so I can also see my a/f mix.

Before you drill the throttle blades (!) grasp the concept of "idle bypass air." The function of your T slot is to enrichen the mixture when the throttle is opened "under load especially." Your carburetor, Holley, Carter, Rochester is calibrated from the factory to work with atmospheric pressure and engine vacuum. Once you start cranking the throttle blades open to compensate for, say 14 hg at idle you have exposed the T slot and now your Idle air bleed is out of calibration because your engine is feeding of of the idle feed and transfer circuit (rich). Take a manifold port vacuum access point and remove your power brake line. Now put a piece of tape over the nipple and poke a 1/16 hole in it and tune your idle.

Go back to your tailpipes and listen and get a whiff. Poke a 3/32 hole in the tape and readjust the idle. Repeat the tail pipe scenario and it sounds smoother and stinks less. Repeat one more time with 1/8" hole and see if you can tune it down one more time. If so you are in the ballpark for idle bypass air calibration and you know you'll need two 1/16 holes (one in each blade) to calibrate the idle bypass, but there is a hitch! Its better to introduce idle bypass air from a non venturi source, hence idle bypass.

If your still confused call: https://cliffshighperformance.com/ and you will learn more than you wanted too. Be patient, and good luck with your tuning!