Trying to get new engine to idle decent runs good otherwise. Originally it would instantly die when putting in gear so I richened up the idle and it would idle at 1000rpm in gear. Should I drill the holes in the throttle plates?
Here is the last tune I tried and it was the worst. Mixture screws had zero affect.

Gen3 Hemi 378cid 13:1 comp
cam 247/251@050 605 lift
dual plane intake
carb quickfuel 950 jets 74/84 PV 4.5 transfer slots both pri and sec opened to .020
vacuum 12-13"
8" 5000 stall Converter
latest timing curve

By transfer slot at .020 you mean what's showing under the throttle blades? I would think it needs more. Is it a 2 corner or 4 corner idle mixture carb?

Yes, I took the carb off and set both equally as best I could. Runs like doo doo now really rich.Carb has 4 corner idle mixture that currently do nothing. I did have running ok but I was running on the primary transfer slot..

you have a fully adjustable carburetor and should not have to revisit the 1980's to tune it.
this should be a simple idle air bleed change
where are the idle mixture screws set? should be between 1-2 turns out.

joe

I’ve had a lot of carburetors on my cars over my lifetime and have never had to drill holes in my plates. Never had to never will

Take the dang speed idle setting off of the transfer slot( the throttle plates need to be below that slot ) and make it idle on the idle circuit only
There have been many bad myths posted on here by people who took a short cut instead of fixing the real issues with the motors and carb tuning The reason the idle mixture screws are not working is your motor is not idling on the idle circuit, it has all the fuel it needs now coming from the transfer circuits
Start over with both idle speed screws unscrew away from the throttle linkage and then turn both screws in one full turn and see if it will idle in neutral and in gear, if it won't add one full turn on both idle speed screws until it does, it shouldn't drop more than 300(100 to 200 RPM is the best) RPM from in neutral going into gear
Once you have it there then slowly try tightening up the (leaning it down) idle mixture screws 1/4 turn at a time, one at a time and then do the other three.
You should be able to make the motor die from being to lean by adjusting one mixture screw too lean for the motor to idle on
BTW, what do you mean with the "latest timing curve"? What does it idle at and where, what, RPM, and how much total timing does it have a what RPM also? I have no clue on the new gen 3 hemi ignition parts or how they are set up
Good luck, let us know your results

If it has something like .068-.073 idle air bleeds drill them out to .075 and see if that helps. I have never had to drill the plates on a carb if the IAB was correct. The timing should be 12-20 initial and 32-38 total. More initial with bigger cam/more overlap. Open chamber OEM style heads seem to like more towards 38 total where the more efficient engines I have worked on like 32-34 total.

I was programming different curves into the MSD ignition controller to see if it would help. The current ignition curve 0-900 rpm ramps to 28 degrees. 900-3100rpm is 28 degrees 3100-5000 rpm ramps down to 24.
The best idle I have so far is 1350rpm in neutral and 1000 in gear but it was running on the primary transfer slot.
Engine will not idle with both transfer slots closed.

IABs are currently .070. I will drill them or pick up some 75s.
Currently I ramp up to 28deg by 900rpm. G3 Hemi's are supposedly very efficient and don't need a lot of timing.

You might want to try between 14 up to 20 degrees at idle up to 2000 RPM and up to 30 degrees above 2000 RPM
That carb should idle on the idle circuit only unless one of the idle fuel feed circuits is plug up or maybe it is defective
When you open up the air bleeds, all three circuits or two circuit carbs., you are leaning that circuit out, if you make the air bleed holes smaller you will richen it up

Open up both sets of plates, primary and secondary , evenly so it will idle on both idle circuits front and rear

Actually some Holley carbs come right out of the box with the primary plates drilled with a .125 hole in each one. Ron

Yes but technology has changed and carbs are more tunable now. And like you said some carbs came that way. No longer needed.

I still think it depends upon the carb and the application. Every Braswell 4760/4825 or Braswell-modified Holley 4150 I've seen over the years (and that includes what they're selling new today) has drilled throttle plates.

If you can't get the ide speed up where it needs to be unless you're off the idle circuit and the carb doesn't have an internal bypass air bleed adjustment that can be tuned, what other choices are there?

FWIW, I'd like to hear from the OP on how the carb ran out-of-the-box, since the settings he posted above aren't. Also, I a$$ume he's tracking AFR, too, and wonder what he's seeing.

you don't really have to adjust the prim and sec blades so that the transfer is exposed the same amount for each.
the baseplate might have a shorter transfer slot on the secondary side. One way to do it adjust them evenly and expect the secondary side to be hidden or just on the verge of peeking past the blade.
I usually adjust the front to roughly .020 exposed on the transfer slot and then adjust the rear to show about the same area of light showing as the primary side if i hold the carb up to some light and look up through the venturis from the baseplate side...
a good starting point at least.
from there roughly adjsut the prim and sec sides evenly to get your idle speed.

Exactly... Technology has changed but my old Holley DP (2-corner idle) and mushroom cam hasn't With the transfer slots "square" on primary and secondary, and PCV operating, the only way to get enough additional air into my 451 with 272@.050 cam was to drill all four blades. Don't remember the size right now but think 3/32". Now it idles at 1000-1050 at 7"Hg.

Someday I'll spring for a 4-corner carb and have Thumperdart go through it

He can convert yours, if he still does that
I shoot for 14.3 to 15.5 AFR at idle by restricting the idle fuel feeds on 4 corner carbs, that usually results in less than 300 RPM drop from idle to neutral warmed up.
My old pump gas 518 C.I. six pack motor with a solid roller cam with 260 @.050 on the intakes with a 108 LSA installed at 106 ILC would idle at 850 RPM in gear and at 1000 RPM in neutral with 14 degrees timing
It wasn't easy to get the carbs, all three of them, to do that but it was well worth figuring out how to do that

OP - How far would you have to drive (or tow?) to Sterling VA from where you are in MD to see if this one runs better / worse / no differently? Oh, look... holes in the throttle plates.

This isn't even a sales pitch, although I do have it listed. If mine runs better than yours, then my tune & setup could help you figure out what direction to go w/ yours.

Besides, I think I still owe you a favor for the Hurst line-lock switch you sent me. - Brad

Braswell still uses drilled butterflies, as do other builders. In some cases, not saying this one it is a useful tool. Not all things old school are totally obsolete

Now they make carbs with built in adjustable idle bleeds. Many carbs need it. To say it's old school and doesn't work or isn't needed is just bullheaded.