thanks Alessandro…...but we need to know why the mixture screws have no affect on idle when adjusting, only on acceleration!  and why the car putters more as it idle, then just Rapidly dies....

Its knowing symptoms, like a doctor....when this is happening, its because of this or this...….

aside from these the car has never ran as strong and efficient....acceleration (when it chooses not to shut off) is Snappy and strong, passing is impressive like its never been and highway is great.....

these symptoms only occur during low warm idle??!?!?!?!?!

I always "harp" on this.......what is the timing set on?
IF the carb is clean and operating properly.....2.5 turns out(on each side)  should be REALLY close to ideal.
Bump the timing up to make it run with the idle mixtures set at 2.5 turns.
Something ain't right if it runs good with the screws bottomed out/all the way in.
Put more timing in it!
6sally6
PS.............you SURE there is no vacuum leaks?!

Good Luck Hudg, let me know what you find and how you make out!

Sally thank you, Im going to be re-checking timing again...that's step one, going to borrow a nice Sanp On timing light cause I think mine isn't working properly!   If I snuff out the Primaries, she dies VERY QUICKLY, so I don't believe there are any vacuum leakes, plus I did the 4bbl intake conversion myself couple months back.  

why would a Carburetor accept mixtures all the way in?  there has to be a "cause and effect" things going on here?
also the Random and Rapid Dying....are they even related?  

I will try to map out the sputter/Die scenario :
Idle in gear at a stop light : Perfect idle -------------------------------------------->.Sputte perfect perfect---------------------------->sputter perfect perfect------------------------>Sputter perfect sputter perfect--------------->Sputter Perfect -----------> OFF!

(     --------> = continued perfect     )

Check the ignition coil.  You could be getting a weak spark as it heats up.

A remote possibility is a sheared roll pin for the distributor gear.  I've sen this happen.  The timing is fine, then the gear spins 180 degrees and causes it to shut off.  On a restart it spins another 180, catches and the engine runs fine.  It should be easy enough to see with a timing light though.  If your timing changes when its sputtering or right before it dies then you've got a timing issue of some sort. 

Mixture screws not working as they should would tend to point to a vacuum leak.  Its getting fuel somehow.  If its not coming from the idle circuit its being drawn out the transition slots by a vacuum leak.  A vacuum leak would also have no real effect anywhere but at idle.  I'd start by running the engine with one vacuum accessory at a time (vac. advance, brake booster, etc.) plugged off and see if the situation improves.  If it doesn't then start checking for leaks between the carb and spacer, spacer and manifold, etc.  Spray some carb cleaner at the area.  If there's a leak the RPM will change and you'll know you've found it.  Of course, Ford small blocks are somewhat notorious for leaks into the lifter valley, which are about impossible to diagnose.  After exhausting all other possibilities I'd pull the intake and change the gaskets. 

My engine was running exactly as M1 described it, the way I interpret it. This morning I turned down the idle as low as I could without the engine quitting knowing that it would quit without warning. I turned both mixtures out several turns and had to turn up the idle till it wouldn't quit. Then I was able to slow down the idle speed and back off the timing to slow down the idle RPM even more. I then disconnected everything that was hooked to the the vacuum ports. I didn't have a tach but it was probably idling around 300 - 400 RPM. I connected my vacuum gage to one of the ports in the intake manifold and noted that vacuum was 15 inches and rock steady. That tells me the engine is in good shape. I adjusted the idle mixtures according to the gage both in and out looking for the highest reading. The left side adjusted, the right side didn't. It didn't even think about moving the gage needle. I took that mixture needle out while it was running and there was suction at the needle port but the gage or engine RPM (still at 300 - 400) never changed. My guess is that side is not getting gas and the carb has to come apart but I thought that the vacuum needle would move but it didn't. I set up the timing by guess and adjusted the idle again then drove it around a little hammering the gas then the brakes and it didn't never did quit. But now it runs like it has bad plug (yellow) wires or spark plugs or gas intermittently working in that one port.

Last edited by HudginJ3 (12/22/2018 5:32 PM)

I do not claim to be EXPERT, but I do have a lot of experience doing it wrong, and I have learned that usually teaches me more than doing it right.

That said...  Idle screws have nothing to do with anything except idle mixture, and a little ways into the "transition" part of the carb.  Sounds like a passage is clogged up, or maybe the secondary idle speed is not correct.

Once you get it adjusted as good as you think you possibly can, remove the carb, turn it upside down.  (I know...some would continue with DROP INTO NEAREST TRASH CAN), and inspect the idle transition slots that are vertical in the carb venturi, right where the throttle blades touch the sides of the bores.  The slots are about 3/16" long, and should only have a section in the form of a square showing below the blades.. If more than that is showing, turn the secondary idle speed screw about 1/4 turn.  That screw is only accessible from the bottom of the carb.  Then, reinstall the carb, start the car and you should be able to reduce the curb idle speed a bit, which will shorten the exposure of the transfer slots.  This will improve idle and also help with the idle mixture screws showing some change when they are adjusted.  However, if ONE of the screws has some affect while the other does not, you may have debris in one of the small air passages or even in one of the idle fuel passages.  If so, disassemble and blow carb cleaner followed with compressed air through all the passages.  Make sure the passages blow all the way through.  None of them blow into dead-ends.  Make sure ALL passages are clean.  Use eye protection, as they can sometimes blow back at your face. 
This leads into a suggestion to NEVER dip a carb in cleaner.  In my experience, it can cause debris to settle and get lodged in he tiny passages. Cans of carb cleaner come with those little plastic straws, and they are great for cleaning passages.  But, be careful as they can flow right back at you if they flow against a blocked passage.  Pay special attention the holes around the rim of the carb's air horn.

Your idle reading were likely taken from the manifold port, which is before the carb's vacuum reading.  While the engine is producing a good vacuum signal, that does not mean the carb itself is not leaking somewhere.
If you have electric choke, be sure the seal is in place between the carb body and choke housing.  Ditto for the vacuum port going to the secondaries, but that one should never see any vacuum at idle.  The biggest problem area on an old carb is the seals on the butterfly shafts, or the bushings at the same place.  If someone used a strong return spring on the carb for a long time, the shaft bushings can be worn and cause vacuum leaks.  You can test that with an unlit propane torch, directed at the shafts, but you need to have something on top of the carb to keep the propane from being sucked straight into the carb top.

An engine cannot properly run if the carb mixture screws are closed.  It may run, but something is wrong.  It will not run CORRECTLY.

Be sure the needles/seats are clean and float level is properly adjusted.  Be sure the choke is not on the fast idle cam.  That will make the carb think it is into transition and make adjustment futile.

Thank You MS......I will disassemble again and reclean, this time with compressed air!

one grey area for me is what you meant at the end with the choke/fast idle cam......what do you mean "make sure its NOT ON the fast idle cam" ?  ------------ are you saying the Fast Idle Screw is not Always in Contact with the Fast Idle Cam?

Another thing you can do is to replace that small slotted set screw that holds the secondaries open a bit with a screw and a nut.  There is enough room around most intake manifolds so that the screw clears.  The nut is used to tighten against the bottom of the carb to ensure the screw doesn't back out.  Now you can adjust that secondary idle without taking off the carb.  You could use an Allen set screw for the same adjustability, but it's hard to find one long enough and in my experience the fit is a bit loose to be sure it stays in place.