I am stumped : carburetor issue

[catdoctor]

I have a 3012s carter AFB on my 348 with auto trans. I believe this is a manual trans carb. When I slowly apply throttle like driving it into the garage it has a flat spot and will often shut off if I don't pat the throttle some. Otherwise the carb performs great as well as the secondaries opening. I have disassembled and cleaned all the ports and slots in the idle circuit as well as the rest of carb, Jets and rods are correct. The step up is metal color. The engine has to idle around 800 rpm or the engine will die when you put trans in gear, in gear idle is 550 rpm. Both idle mixture screws will adjust idle quality and are 2 turns out. Timing is 12 no vacuum to dist.@ idle. The manifold vacuum at idle is 15 hg idled up 22 hg with the 262 cam 212 @.050 very slight lope. Total timing at idle with vacuum to distributor is 22. All in vacuum and centrifugal is 32 @ 2800 rpm. SOOOOOOOOOOOO

I took it off and didn't change any timing settings.
Installed a 250 hp Rochester 4gc. It works perfectly. Idles at 675 rpm and in gear 600 rpm. Idle is strong with no hint of going dead .

On the Carter carb I also checked with propane for vacuum leaks around the throttle shafts as well as with carb cleaner. The accelerator pump is the correct length and I adjusted the 1/2 above the body.

I really want to figure this out as the carter AFB goes with the intake.

Have any of you experienced this issue?

 

[oldskydog]

 

[oldskydog]

 

[catdoctor]

Thanks Oldskydog. I appreciate you taking the time to post the bulletins. I will review and make sure I didn't miss anything.

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[MRHP]

And also remember, the fuel formulation now a days is different than back then. Jetting will most likely need to change for the richer to correct any drivability issues. Seems accelerator pump, or off idle circuit may need some attention From the symptoms you describe.

 

[427John]

MRHP hit the nail on the head, with the difference between fuels from the 50's and 60's (no ethanol) to todays gas I would be totally surprised if the factory calibration for the carb still worked it will probably want a little more fuel in most scenarios including accelerator shot.

 

[Skip FIx]

One of my Mopar buddies using a wide band even saw big swings between batches at fill ups with pump gas!

 

[409newby]

Ported vacuum could be part of the problem I would switch to full time vacuum and see if that makes a difference

 

[catdoctor]

Yes on the full time vacuum. The 4gc is working great. Probably some time down the road when I have more time I may remove the two plugs on the front of the Carter carb and see if there is anything restricting fuel flow at idle. Thank y’all for your thoughts.