Howdy,
Looking for some advice or guidance for tinkering with my carb. It's a Holley on my '66 352. Engine starts and idles with the choke **** pulled half way out reliably every time. Only issue comes with maintaining the idle once the engine is warm. The engine will fade off and die after the choke is only a quarter of the way out after pushing it back in a bit. Not sure if I should be adjusting my fast idle adjustment screw, my normal idle screw, or my mixtures. Carb has been rebuilt and tested on a 350 test engine but not tuned yet!
Thank you to anyone willing to respond!

 

Since it worked on the stand, I wouldn't rule out an installation issue. Double check everything.
It's always good to look at ignition before carb issues, but since it runs choked, probably not. However I would check dwell and timing at some point, if you're not sure where they are.
It sounds like a vacuum leak symptom, so while double checking installation, I'd look thoroughly for a vacuum leak before any adjustments. Maybe one of the ports isn't plugged, hose not landed correctly or cracked, PCV not working correctly, vacuum advance leaking, gasket not sealing, or some manifold vacuum leak...
After that, I'm thinking I would crank up the curb idle to get it at least running without the choke - or just put your foot into it - to see what RPM it will hold idle. If it's not too high - say 1000 or less, you can adjust the idle mixture while running, and see what happens. If the idle is much higher, the butterfly is past the idle circuit and the idle mixture can't be set correctly.
Setting the idle mixture blindly may be what you need to start with. Screw the needles in until they lightly touch. While doing so, count the number of turns it takes. If it took less than 1 turn to seat, it was probably set too lean. Then
Back them out 1.5 turns - That's a regular starting point. Then see if it will idle. (BTW, some Holley's have a reverse idle mixture screw - I had one on a 302 mustang back in the 90's)
If it won't idle, back them out another turn and see what happens. And fiddle with the curb idle screw to see if you can find a working spot that is less than 1000 rpms.
If you can get it idling, then set the idle mixture to achieve maximum vacuum or maximum rpm, then readjust curb idle
If you can't get it close, I might check timing and dwell while it's idling choked.
Otherwise might be the idle circuit is clogged or the floats need adjustment

 

@F250 4x4
You have had more than one carburetor apart in you days. hahaha

@samthetruckman
Don't feel bad, there are lots of things that can be off-kilter in one of these carbs. I'm guessing your's is a Holley 2-bbl, or Motorcraft ?
Like F250 mentions, the throttle plates must be cracked open slightly for the idle circuit to be drawn from (hence the "slot" in the bore.
I just rebuilt one of these, a Holley 2300, 1962 model, and noticed the throttle plates were closed completely. I thought to myself, "open them up to the "slot", and then got derailed and forgot. I put the carb on the engine and fired it up and no idle. But, the engine would run "partial choke" which I think opens the butterflies partially. I got rained out, and as I was putting tools away in desperation, I happened to remember those pesky butterfly plates never got opened by me. How do we find a good reliable Techie today ? hahaha

Therefore, next time before I start it up, I'm gonna jack open the throttle butterfly plates about .030-inch for starters.

Here is an idea:
It wasn't mentioned earlier, but if you do have any doubts about your timing, simply advance it until the engine kicks back against the starter.
Then, simply back off the distributor (retard) about 1/2 the diatance between two spark plug wires on the cap for rotation.
At that point, you are Close. If the carb is off, then check the relationship of the plate and the idle discharge slot. Plate should cover no more than 1/4 of the slot.
Fire up the engine and play around with the throttle plate set screw for lowest speed.
If all is good, if you screw in one of the idle mixture screws all the way in, the engine should die. That tells you the mixture screw is working.

This may or may not be of assistance, but when it comes to carburetors, we need all the help we can get. right !

Let us know what fixes the issues so we can all learn.

 

If you are still running a points distributor, be suspicious of the condenser. When they go bad, they can cause a wide range of odd symptoms that'll keep you chasing your tail.

 

your symtoms sound so much like mine. i have a '66 with a 352, 2bbl carb, bone stock except for an open element air cleaner. i had my truck running nicely. one day the idle simply deteriorated and i couldn't keep it running long enough to diagnose anything. today i was off from work and i said i'm gonna end this.
first off, i checked for spark. it was non existent, then sporadic.
i found 2 questionable plug wires. i replaced the set, installed a new set of points and a condenser. i also cleaned the contacts in the distributor cap. i also set the timing and leaned out the carb with one turn IN of the idle mixture screws. double checked the float setting (it was dead on at 17/32")
all of that and the truck starts, idles and drives like new. i think i was chasing too many things and not focusing on one problm at a time.
i don't know if this helps or not. but one thing this lesson did teach me: be thorough and start simple.

 

After cleaning and install of a carb kit, on my '62 Holley 2-bbl "2300 series" (supposedly), it wouldn't idle without using the choke. defeated again.
That was late Wed afternoon. That was perplexing where the engine will run, and with a fast idle beacuase of the ramp-up on the choke cam.
Open the choke, which closes the butterflies, slowing the engine down to idle speed. Sounds good but the engine would drew down below idle and quit. Done.
At a guess, I had turned the "idle mixture screws" out 1-1/2 turns for starters. After farting around with the idle fail, I figured I had better screw the idle mixture screws in 3/4 turn or half of my original guess. So, now, i pull choke out 1/3 and hit the starter and the thing races to a high idle. Nice ! it is actually running on it's own, and the plastic tank from the Rototiller. hahaha (if the wife finds out, i'm dead meat). She reluctantly is the "pedal-girl" while bleeding brakes.
Where was I, thinking of bleeding brakes, I always spent hours making sure the brakes on our old '71 Winnebago Chiefton were Top Notch. memories

Currently, as I continue here, the 292 engine is idling high-and-happy. Now I begin to ease those idle mix screws in and out for the sweet spot.
Repeating with the other screw, slowly in and out until best idle.
Next is back to the idle speed set screw and slowly back it off for slowest idle speed.
Next, is Repeat the aboe two steps slowly woring the idle mixture in and out for best vacuum or rpm or "seat-of-the-pants" feel.
Then after that ease the idle speed screw off slightly to drop the idle speed more down to around 600-rpm's ?

I added a quart of ATF to the engine oil before firing the engine up earlier in this effort to get the engine running again after 18-years since last driven.
The oil looked quite clean after sitting still and any debris settling out in the 18 yesrs the pickkup has been resting. It was near a quart low, so the ATF brought the level up to snuff. Also, too, for lubing those intake valve stems and cylinder walls, I am running 32:1 two-stroke fuel mix. I'm superstitious.
I kept lowering the idle down to where all seemed good.
I'm ready for a break to celebrate getting tha engine to idle, and with the fuel level sight plug removed, the fuel lever was right there with engine idling. If I rocked the pickup, fuel would spill out. Perfect. I'm tickled pink. So, for curiosity sake, I shut the engine off, and hit the Starter again and it fired right up and behaved.

I'm still in shock of how sensitive the idle mixture screws were in relation to the idle speed screw which controls the butterfly plate opening amount.

I actually ran the engine long enough for the Temperature Gauge to respond ! Bonus
About that time as the engine was warming up, i noticed a "Spring" of coolant coming out from the weep hole at the bottom of the Water Pump.

Can you see where this is Leading ?

Keep fidgeting with the idle circuit settings as they had me stifled for awhile.

One last thought: check the Idle air bleed inlet jets.
They are down inside the air horn, and I believe they are the larger outboard inlets looking down (two smaller ones inboard).
A piece of debris can easily fall down into one blocking it.

 

Libel to run a skosh better when you aren’t running 2 stroke gas perhaps.

 

The engine must be at fully warmed up before idle speed and idle mixture can be adjusted. If you adjusted it before it was all the way to full temp then it'll be off when it's at full temp.

I use the "Lean Best Idle" adjustment method as described in the Weber carb setup instructions and have a dead-steady idle speed even with widely varying temps and elevations, sea level to 7000 feet and teens to 100*. We had one of my carbureted car on a friend's dyno in Phoenix a few years ago, along with a few other efi cars and all of the efi guys were baffled that mine had the most stable idle speed of any of them.

CARBURETOR SET UP AND LEAN BEST IDLE ADJUSTMENT

 

A lot of informative people here... thanks to everyone for all the great information! I've gotten the truck idling and driving around the yard now after some tinkering. Having lots of fun learning this carburetor business as well!

I'm running mmo in the fuel due to a friend's recommendation but don't think I'll continue doing so just to compare the difference in performance.