• When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.

Carter #4401 AVS carb info

Geoff 2

Well-Known Member
Local time
4:23 AM
Joined
Jul 21, 2014
Messages
1,964
Reaction score
1,280
Location
Australia
I am rebuilding the above & have noticed something I have not seen or [ noticed before]. The carb is in exceptionally good condition & appears to be original, has original rods & jetting.
It has an adjustable idle air screw [ LH thread ] but no visible idle mixture screws. It does have mixture screws but they are hidden behind plugs. I have seen these before.
With the pri t/blades cracked open with as little as 0.020" of t/slot showing, the vac adv port is exposed. The carb, as received had about 0.060" of t/slot showing which exposed all of the vac port. I don't know if this was how it was run on the engine it came off. If the t/blades are closed so that no t/slot is showing, the vac adv port is no longer visible.

So my question is: since carbs normally have some t/slot showing at idle, on this carb vac adv would be activated. So is this carb designed to work on manifold vac adv at idle? Or.... Is the carb designed to run with the blades nearly closed, no t/slot showing at idle, & run with ported vac adv?
Thanks.
 
There is only one source for vac advance on these, ported.
 
There are two (2) factory set and sealed, behind small lead plugs, adjustment screws, in the base casting, perpendicular to the primary throttle bores. Dig out the lead plugs, using a small screwdriver, turn out approximately 1/4 CCW, the idle quality will be vastly improved. The top mounted left hand thread MIXTURE screw is really an adjustable air bleed. Surprising that you don't know this, as you seem to present yourself as a self-proclaimed expert in everything automotive......
BOB RENTON
 
Bob,
I did know about everything you said because I have playing with these carbs since the early 70s. If you actually BOTHERED to read what I said, I mentioned both the mixture screws & the idle air screw. You think it is odd that there may be someone else in the world other than you who might know about these things? After all your blustering, you failed to offer any answers to my question. I do not normally reply like this but your rude reply was over the top. Thanks for nothing.
 
Turbine,
If it is designed to use PVA, then the blades would have to be nearly closed, with only a tiny bit, maybe 0.010" or less, of T/slot exposed at idle. Do you know if this is how they [ the blades ] are set on the engine?
 
I am no good with computers. I will try & take a couple of pics of the above & get my son-in-law to load them.
 
I think I have that carb and will look. I believe that carb has the air bypass passages the bring air around the blades and direct some flow across the throttle bore below the blades. So yes the throttle blades would be more closed then a prior year AFB. The 68 Carb service highlight discusses the air passage. I would also imagine the timing of the vacuum port opening is earlier since this is the emission year for all cars and initial timing values and distributor mechanical advance is different.
 
Turbine,
If it is designed to use PVA, then the blades would have to be nearly closed, with only a tiny bit, maybe 0.010" or less, of T/slot exposed at idle. Do you know if this is how they [ the blades ] are set on the engine?
I can check a 4429 that I only use for certain shows and take some pics later today.
 
I checked and yes air bypass and yes very little transition slot exposed. Not sure it is .01 maybe .020 or so before vacuum port begins to be exposed, but you have idle air available via set bypass. These engines are emission engines so idle is low and timing at idle is designed to be low.

Interesting enough I looked at a 68 hemi AFB and port location is similar, but again these are emission carbs and the Hemi timing in 68 like the 383 was 0 initial. So vacuum had to start sooner and idle RPM was only 650rpm.
 
Thanks for the replies. I hope to have some pics later today.
 
DSCN0233[1].JPG

DSCN0229[1].JPG

DSCN0205[1].JPG

The lower pic with white paint is a 4429 750 AVS. Note with about 0.060" of t/slot showing the VA port is visible. The other two pics are the 4401 625 AVS. Note with about 0.040" of slot exposed, the VA port is exposed & the VA would activate. The pic showing just 0.020" of t/slot showing, you can just see the VA port. So if the 625 carb was run with the normal 0.040" -ish of t/slot showing at idle, the VA would be activated at idle. The difference between the two carbs is that the t/slot on the 625 starts about 0.050" higher in the throttle bore. Is it a manufacturing fault?
 
So I looked at several carbs and there does seem to be a variance. I have the 4426, 4966, and 4639. The first is 4426 68 383 4spd and it has largest amount of t slot exposed at closed throttle, the 4639 69 340 AT had similar closure to your 4401 which is 383 AT. The 4966 which is a later year LP 440 AT carb was in the middle of t slot exposure.
So I guess you do need to see another 4401 to know for sure.

If you want manifold vacuum on distributor, I guess this is your carb. If you don't you could slot the bottom of the blade at T slot location to expose the amount of t slot desired.
 
Thanks for the reply & going to the trouble of checking out your carb stock. When you say the 'largest amount of t slot exposed at closed throttle', did you mean 'the largest amount of VA slot exposed at closed throttle'?
I found this with the three AVS carbs I have: the VA port is the same distance above the base flange on all three carbs. What is different & causes the relative change in exposed VA slot is how far up the t/bore [ from the base ] that the T slot begins. The overall length of the slots appears to be the same.
What intrigues me & why I started the thread is this: did some of these engines/carbs have VA at idle, either by design or by fault?
 
What I looked at was blade closed, VA covered, how much transition exposed. I did not measure how much blades opened to expose VA.

There is no Mopar literature that talks to using VA to increase idle timing that I have read.
 
I had the opportunity to look at another 625 AVS today, #4934. It was used on Aussie 340s. With 0.040" of t/slot exposed, the VA port is not visible, unlike the 4401, which seems to be an orphan...
 
Auto Transport Service
Back
Top