Is anyone running a 4425S Carter on a 68 340 engine?

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Hyper_pak

Hyper_pak

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I have one I am looking at using and I notice it only has 1 idle circuit screw.
There are 2 small holes below a couple of capped passages that don't look used.
Just wondering if it's stock or am I missing some parts.
Thanks for any info.
 
I believe at some point the dual idle screws were abandoned for a single screw. (I seem to recall something aubout it being an air bleed vs a fuel volume change, but don't quote me on that)


Screenshot_20220327-190733.png


The plugged holes are probably there from passage hole drilling


Also check the FSM for the correct year of the carb that should tell you a lot.
 
Some of the earlier carbs only had one screw. The early AVS carbs on 68 340's for example. My 69 340 has two screws.

20201129_144834.jpg
 
Maybe it's a CAP like thing.

My CAP 67 4 bbl has 2 screws the non CAP also has 2.
 
The 4636S on my '68 automatic car has only the one screw. According to manuals it is the correct carb for the car.
 
Yup. Look at the exact service manual for the carb. Also check the TSBs (at Hamtramk Historical).
Many of the CAP carbs got a more limited range of idle mix adjustment. The single screw is almost certainly an idle air bleed adjustment screw. Some of the two adjustable screw carbs are also into the air bleed passages.
To meet idle emmissions these carbs were meant to be finely adjusted using a CO sniffer. The goal was a relatively lean idle mix, around 14.2 AFR by '69.

Mymopar might have a better scan
1968 Chrysler Imperial Carburetor Service And Repair Highlights from the Master Technicians Service Conference Session 243
 
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All 1968 AVS’s have one screw and lead capped base plate screws. Sometimes you can pull the caps off and adjust the screws. I couldn’t with mine.

1968 engines with AVS’s on 340, 383, and 440 had them. 1969, 1970, and 1971 AVS’s have two exposed adjuster needles in the baseplate.

I had a 4425 on my 1968 340 in my barracuda. Changed to a 1850 Holley 600 cfm vacuum secondary. Not a big difference. Not that an 1850 is anything real special.
 
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There are idle mixture screws buried under the lead, just below the 2 aluminum plugs. Good chance that they are frozen. As Mattax said, that top screws controls idle air only.
 
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