I recently installed a OEM 6 barrel on my GTX and am having a major problem at idle. I have to idle at 1400 rpm for it to stay running. It runs fantastic otherwise and you can feel and hear when the outboard carbs kick in. The center carb is a 4144-1 type. I have heard automatics and manuals use different carbs. Mine is an automatic.

 

A wrong carb should not cause that problem. Part of the reason different carbs were used was the "last little bit" to meet emissions.

The usual applies..........vacuum leaks, someone has screwed with your carbs and they are not as they should be, etc, etc.

If things get REAL bad to find, I would remove the outer carbs which DO have (sealed) idle circuits, and make block off plates out of something simple like empty beer / soda cans.

Are you running a mild "close to stock" cam?

Do the mixture screws have good effect?

What is the timing? And by that I mean WHAT is the timing, not "some guess."

Vacuum leaks? Booster? Hoses? Squirt water around the carb bases, etc

What does it "act like?" Too lean? Too rich? Only running on one barrel?

 

Listen to 440roadrunner, he knows his stuff. My first thoughts when I saw your post was ignition timing and vacuum leak(s). Keep us posted on your findings. FYI, I've had good luck with the base timing on 440s at 14 degrees btdc (vac advance capped off to set initial). Good luck

 

vacuum leaks? get a small distributor vac hose and put one end in your ear and pass the other end near the mating surfaces if it has a leak you will hear it. or spraying WD-40 at the same spot will change the idle speed, if you have a leak.