Dialing in a Carter AVS

Hello Folks,

So this past weekend I was finally able to break in the 440 for the 70 Charger my old man and I are working on. So my dad is very old school and sadly the term "cant teach old dogs new tricks" resonates very well with him... With that being said he was adamant that he never heard or had to break in a cam before, even after I showed him the break in procedure from the cam company he was still reluctant, but I did it anyway.

With that being said... we are running a Carter AVS (not to sure of the part number, silly me didnt check before I left...) because those were the "best carbs around". So trying to get him to switch carbs is going to be more hassle than it is worth. The engine is a fairly stock rebuild. It was bored .020" over and has a hotter cam in it. I have the cam card, just not in front of me at the moment. What I do know is the valve springs didnt change that much stock, so I know it is not overly wild. My question is if I could use the Edelbrock calibration kits to help dial in this carb to get the most out of the car? and if so which one? I have heard you could but really couldnt find much information out there as to which kit to use. I believe carter had these strip kits back in the day, but finding one is difficult and I saw the prices are astronomical.

I believe the AVS is a 3 step metering rod and the edelbrock utilizes a 2 step rod similar to the AFB. What would be the disadvantages/advantages of switching the AVS over to the 2 step rod set up?

I am just trying to make sure this engine runs right and I dont have an overly lean or overly rich running engine that would only cause maintenance head aches down the road.

Thank you

I used the Edelbrock strip kit in my 625 Carter AFB, 2 step rods. Direct interchange between jets, rods, springs. Your AVS has 3 steps. See if you can download the tuning guide from Edelbrock as it's very useful. If you can't find it call their tech and tell them you have their carb and they might send you a PDF.

I'm no expert but I'd say the 3 step will give you more precision during transitions.

This carb is on my warmed up 318 and the plug readings are the best on any old car I've owned.

The 3 step is more precise BUT to dial it in like a factory set up carb is stupid hard. For ease of tuning & less math, use the flat covers from an AFB or the Edelbrock AFB so you can use the 2 step rods. The AVS rods are longer. That's why the rod covers have a dome.

Another good thing is the AVS has the boss mounts to drill and tap for the electric choke.

Edelbrock so SUPER STRONGLY SUGGETS that in NO WAY should you never use there parts on OE equipment. I have found it works just fine.

Thanks Rob! I never realized rhe interchange "fix" with the different covers!

rumblefish360 said:

The 3 step is more precise BUT to dial it in like a factory set up carb is stupid hard. For ease of tuning & less math, use the flat covers from an AFB or the Edelbrock AFB so you can use the 2 step rods. The AVS rods are longer. That's why the rod covers have a dome.

Another good thing is the AVS has the boss mounts to drill and tap for the electric choke.

Edelbrock so SUPER STRONGLY SUGGETS that in NO WAY should you never use there parts on OE equipment. I have found it works just fine.

Click to expand...

Thank you all for the replies.


When on their site I see they have multiple strip kits for this style carb:

Performance Carburetors and Accessories - Calibration Accessories - Edelbrock, LLC.

How do I know which one to use for an AVS?

Joe

Find out whawhat size jets and ride are in there now. Select the kit with the closest rod and jets sizes.

If you have a 750 AVS then I would use one of there 750 jet kits. I do not know the differences between there AFB and there Thunder series AVS style carb. If there is any at all.

Generally speaking, the kit should have the ability to enrichen or lean out the carb from its base settings. For the most part, you will not need wildly larger or smaller jets.

The AVS Thunder kit I have has .092, .095, .098, .101, & .104 jets with .065/ .037, .042 & .047, & .070/.047$ .052 rods.
This gives you 25 combinations. Limited I know.

The older Carter strip kits have much more! If you can find one of those complete (or close) the 10-201 kit for the AFB has 6 rods & 16 jets for primary & secondary tuning.

If you have an original 440 AVS run it as is first. The HP ones are great out of the box. If you want to switch to the 2 step system, I don't recommend it, you have to switch primary jets to the standard low jets, 2 step rods, and the flat "hats". I have seen lean condition in part throttle cruising with perfect idle and WOT. There was a reason they have 3 steps. If you need richer mixture you can carefully sand the rods or drill slightly larger, .002 to .003 thousandths, holes in the high primary jets. The best start is to see what you have. Then calculate the area of the jet and subtract the area of the rod.

Oh crap! Thanks, I forgot about the change of jets.

I have about the same combo that you have and ran it with a stock 68 440 AVS with out any changes and it ran fine.

I appreciate all the replies!!

and yes I do agree that I need to set up what it has on there now and see how it runs. But just trying to see if there is anything I can do in the mean time or prepare for.

rumblefish360 said:

Oh crap! Thanks, I forgot about the change of jets.

Click to expand...

You're not the only one. Just went through a 65 273 AFB and they jammed 2 step rods through the tall jets, bent them and all. Bet it didn't run too well???

Okay this has been awhile since I touched this subject but I finally got other projects to the point where I needed things to do and this was it, dialing in the charger. So far this is what I know:

it has the 71 440 carb 4966s. However, in 71 they had two avs's for a 440 automatic, well it turns out this is the non-hp version (a guess) since it has the smaller bore (1-7/16 to the 1-11/16), venturi (1-3/16 to 1-7/16) and primary jets (.089 to .101). I thought I found the 70 440 AVS version in my carb stash (which was sized the same as the 71 440 HP carb) but as I tore that down I realized that was my dads "parts" carb and was junk.

I have been chasing what I believe is a lean issue on the car as in it burns your eyes to stand near it while running at idle. So when I tried to rebuild the 70 440 AVS (and found out it was junk) I tore into the the 71 440 AVS that was on it. It had the correct jets, but the incorrect rods. It should have the rods that measure .065x.062x.053 but had the rods .0675x.064x.058. I believe I found my lean issue...

Now, I know this carb is not optimal for this car, but the vacuum readings I got on it are as follows:
idle in neutral: 12-14 inHg
idle in gear: 8-9 inHg
cruise: 15-20 inHg
WOT: 1-2 inHg

I put the correct rods back in the carb from the junked 70 AVS, but I believe I have a couple other AVS's that may have the .101 jets in them (since finding the carter strip kit 10-106 or 10-202 is either impossible or cost prohibitive) that I could rob out. Would there be an issue running this carb that has smaller primaries with the .101 jets with the proper rods?

I can’t answer the tune question outright. If the stock jet and rod have a .030 difference (100 jet .070 rod) then using a smaller primary carb with the same rod and jet would have it run rich because the smaller bore will have a higher velocity and pull more fuel.

This would also be true if you used the same carb and altered the rod & jet combo to .110 jet and a .080 rod. The reason being is there is more circumference even though the math would say both rod and jet have the same clearance between them.

Your best bet is an 02 sensor or take your time reading plugs and experiment.

Instead of searching for an old tuning kit, did you think to use an Edelbrock kit? If your AVS has the 3 step ride and high cover, you can switch to the AFB 2 step rods and the flat cover.

If your eyes are burning I believe it’s running rich and not lean.

Burning your eyes IMO, is always a faulty transfer slot sync, which either leads to too much Idle-timing or is caused by too much Idle-timing.
Don't blame the carb for this!

I have never ever had this problem not go away after the transfers to timing thing is worked out, sometimes with a little bypass air thrown in.

carfreak6970 said:

.....since finding the carter strip kit 10-106 or 10-202 is either impossible or cost prohibitive.....

Click to expand...

Well, not totally "impossible" to find, but you might be right on the "cost prohibitive" part.


What constitutes "cost prohibitive" to you???

carfreak6970 said:

Okay this has been awhile since I touched this subject but I finally got other projects to the point where I needed things to do and this was it, dialing in the charger. So far this is what I know:

it has the 71 440 carb 4966s. However, in 71 they had two avs's for a 440 automatic, well it turns out this is the non-hp version (a guess) since it has the smaller bore (1-7/16 to the 1-11/16), venturi (1-3/16 to 1-7/16) and primary jets (.089 to .101). I thought I found the 70 440 AVS version in my carb stash (which was sized the same as the 71 440 HP carb) but as I tore that down I realized that was my dads "parts" carb and was junk.

I have been chasing what I believe is a lean issue on the car as in it burns your eyes to stand near it while running at idle. So when I tried to rebuild the 70 440 AVS (and found out it was junk) I tore into the the 71 440 AVS that was on it. It had the correct jets, but the incorrect rods. It should have the rods that measure .065x.062x.053 but had the rods .0675x.064x.058. I believe I found my lean issue...

Now, I know this carb is not optimal for this car, but the vacuum readings I got on it are as follows:
idle in neutral: 12-14 inHg
idle in gear: 8-9 inHg
cruise: 15-20 inHg
WOT: 1-2 inHg

I put the correct rods back in the carb from the junked 70 AVS, but I believe I have a couple other AVS's that may have the .101 jets in them (since finding the carter strip kit 10-106 or 10-202 is either impossible or cost prohibitive) that I could rob out. Would there be an issue running this carb that has smaller primaries with the .101 jets with the proper rods?

Click to expand...

What is wrong with the "junk" 440 carb? What number is it? Did you run the 4966s carb before you started changing things? Was it OK except for the burning eyes at idle?

I just assumed it was running lean due to the eyes burning because I thought rich it would be smoking a bit out the tail pipe? It is running the stock cast iron 4 barrel intake, stock exhaust manifolds and comp cams part number 21-224-4 (grind number XE274H-10). So since this would be a little hotter than the HP engine I figured it would need the .101 jets with the .065x.062x.053, but instead it has the .089 jets (the one the 4966s carb was to have) with rods that measure .0675x.064x.058. Those parts make it appear it is running lean, correct?

I did think of modifying it to use the AFB jets and rods, but some people argue that you miss out on the smoothness of the 3 step rod. Furthermore, if this set up should have the AVS with 1-11/16 why waste more time and money trying to get this 1-7/16 bore carb to work with this engine? I am currently contemplating dropping a new 750 cfm holley on it (or maybe find a 1-11/16 bore AVS), but that wont be for a couple months. So I am just trying to get this to run with what I have currently.

What is cost prohibitive for me? well the one online carb place I saw sells the kits I mentioned above for $500. At that point thats more than a new carb. Id much rather go with a new holley over that.

What was wrong with the "junk" carb? well it was missing parts for one, second after soaking in simple green and multiple runs through my ultrasonic cleaner I still couldnt get it as clean as Id like it to be, plus the drivers side jets were glued in there. Well I dont know if there was actually adhesive holding them in there, but they did not want to come out. I tried drilling them out and I guess the bit went off center and started to cut into the aluminum body. The junk carb was 4738S, so the proper 70 440 carb with the 1-11/16 bores... So I am not to happy about junking this carb.

The car ran OKAY. Cold starting was a pain, but it ran fine. Well besides the burning eyes like you mentioned.

transfer slot sync... (keep in mind the following information is with the 4966s carb) I have been playing around with the timing as well. It idles best around 18 deg BTDC, right now it is at 14 deg BTDC. I had it as low as 10 deg BTDC, but it did not like that at all. The take off at idle is a lot smoother at 18, 14 is okay, at 10 it is jerky. The temperature would start to creep up at idle when the initial was set to 10, it doesnt go up as much when the idle was set at 14, but would idle all day long at 18 with no issue. I get my best vacuum readings at idle when the timing is set at 18 deg (hovering around 14 inHg), were at 10 deg I was getting 11-12 inHg. A lot more of the transfer slot has to be exposed for it to want to idle around 800 rpm at 10 BTDC than at 14 and 18 deg BTDC. Regardless of timing, the idle speed screw is almost maxed out (as in screwed in far enough to almost make the spring go solid) to keep the idle speed around 800. So my thought process was if that much of the transfer slot needed to be exposed, it wants more fuel.

The “Smoothness” of the 3 step rod is a minor thing. It’s nice but you’ll never know the difference. It shows up on the emissions test.

carfreak6970 said:

.....What is cost prohibitive for me? well the one online carb place I saw sells the kits I mentioned above for $500. At that point thats more than a new carb......

Click to expand...

Wow, didn't know they were worth that much, I figured maybe half that. I'd probably go with a "new" carb too at that price. Only reason not too, would be a 100% OEM restoration car.

69DodgeMan said:

Wow, didn't know they were worth that much, I figured maybe half that. I'd probably go with a "new" carb too at that price. Only reason not too, would be a 100% OEM restoration car.

Click to expand...

Well it appears the last time that site was update was 2015. So I am sure the prices didnt change much, only his supply. But yes that is where I am at too, and this is not a 100% OEM numbers car, far from it.

rumblefish360 said:

The “Smoothness” of the 3 step rod is a minor thing. It’s nice but you’ll never know the difference. It shows up on the emissions test.

Click to expand...

Ill keep that in mind if I find 1-11/16 bore carb in my stash.

carfreak6970 said:

transfer slot sync... (keep in mind the following information is with the 4966s carb)

Click to expand...

You are correct that a Carter idle system has a couple important differences from the Holley system. (Discussed here:Operational theory of the Carter idle restricions & air bleeds)

carfreak6970 said:

I have been playing around with the timing as well. It idles best around 18 deg BTDC, right now it is at 14 deg BTDC. I had it as low as 10 deg BTDC, but it did not like that at all. The take off at idle is a lot smoother at 18, 14 is okay, at 10 it is jerky. The temperature would start to creep up at idle when the initial was set to 10, it doesnt go up as much when the idle was set at 14, but would idle all day long at 18 with no issue. I get my best vacuum readings at idle when the timing is set at 18 deg (hovering around 14 inHg), were at 10 deg I was getting 11-12 inHg. A lot more of the transfer slot has to be exposed for it to want to idle around 800 rpm at 10 BTDC than at 14 and 18 deg BTDC. Regardless of timing, the idle speed screw is almost maxed out (as in screwed in far enough to almost make the spring go solid) to keep the idle speed around 800. So my thought process was if that much of the transfer slot needed to be exposed, it wants more fuel.

Click to expand...

Excellent approach.
A couple tips.
* Always note the rpm of the initial. Some distributors will already be advancing at the 'idle' or initial setting. The result is that its not actually the base or initial timing. Instead its base timing plus the degrees advanced at that rpm.
* Best manifold vacuum in neutral (park) is slightly misleading because there is no load on the engine. Go for best vacuum in drive (for a given rpm). In general this will be a 1/8 turn richer on the idle mix screws, and may also be a little less timing.

carfreak6970 said:

I just assumed it was running lean due to the eyes burning because I thought rich it would be smoking a bit out the tail pipe? It is running the stock cast iron 4 barrel intake, stock exhaust manifolds and comp cams part number 21-224-4 (grind number XE274H-10). So since this would be a little hotter than the HP engine I figured it would need the .101 jets with the .065x.062x.053, but instead it has the .089 jets (the one the 4966s carb was to have) with rods that measure .0675x.064x.058. Those parts make it appear it is running lean, correct?

Click to expand...

OK. Lets seperate this out.
Burning eyes can be a mix of unburned hydrocarbons so yes it may be lean at idle.
The rod jet restriction is much larger than the idle resitriction. Significantly larger so it should have no effect on idle mix.

The rods and jetting will only need changing if the velocity of the air past the boosters at a given rpm changes signifcantly. In relation to cam change, this will happen if the volumetric efficiency changes noticibly. I wouldn't try to guess that. Drive it and change the rods as needed for better milage, and better quarter mile mph.

One caveat. I haven't looked up that carb number, but Chrysler carbs from around '68 to '71 or so that were for CAP/CAS engines were set up to run relatively lean idle mixes. This was for reduced CO and HC emissions and only worked when combined with the original everything. With the increased overlap in the cam, a lean idle carb needs to be reworked some. For strong idle with a fully warmed up engine, idle mix will need to be down around 13:1 to be strong.

carfreak6970 said:

as in screwed in far enough to almost make the spring go solid)

Click to expand...

What you are experiencing is lack of idle air bypass.
The engine wants more air, so you crank in the speed screw, which makes the transfers flow too much so you close up the mixture screws ....... So you crank up the timing, to back out of the transfers, and bring the mixture screws back on line. What you are doing is chasing your tail. Everybody does it.
What you need to do is set the transfer slot exposure to be in the ballpark, like to a lil taller than wide.......... and leave it alone. Later on, much later, you may have to fine-tune it just a smidge.
Then set the mixture screws to mid-adjustment.
Then set the timing to whatever gets your idle-speed to where you want it to be; without regard to what it actually is. With an automatic, it doesn't matter what the timing is,until she hits the stall speed. And you can adjust that with rate-of advance ,and the Vacuum-Advance at Part-Throttle.
Then fix the idle AFR with a combination of bypass-air and a slight mixture adjustment, that could be had with
a) a tad more or less transfer, or
b) a tad more or less mixture screw adjustment
c) a tad more or less bypass air.
d) occasionally, the airbleeds for fine-tuning.

Big cams want bypass-air, the bigger the cam, the more bypass-air it will want.
Your 274 cam will want bypass air equivalent to drilling holes in the primary throttle blades of about 5/64 one in each. With that Carter I know of no better way to get bypass air than to drill.

When you get it right, the engine will idle right down to 650 in gear. With a lil less ignition timing, it might go down to 600. If you can get the M-rods to stay down, and with a lil more finessing,and with a heavy flywheel, I see 550 in gear, with a bit of a tendency to not like it, but she'll do it...... at ~5* advance, and with the right AFR. Whether or not she'll take throttle,lol, is another matter.
Just leave that transfer slot exposure alone. That is your main low-speed fuel supply... and your main idle-speed fuel supply. The mixture screws are just for enrichening the idle but if you set them really rich, then, since they never shut off, that means your entire low-speed system will be rich. Try to keep them at 2 to 2.5 turns out.
If you drill the bypass holes too big, the idlespeed will go up, which will require the timing to be retarded more. and to smooth it out will require more fueling, so it's and endless search for the perfect balance of bypass air to enrichment, and jacking with the timing.
I can tell you that a pair of 1/8th inch holes will be too much, and a pair of 1/16 will not be enough,lol, and a pair of 3/32 might be right on. But I suggested a pair of 5/64, one in each primary butterfly, cuz you can play with those for a long time.
If you drill too big,don't panic. You can fill them with solder, move over, and start anew; No big deal. Unprofessional for me, but not so much for you,lol. Just chamfer the holes,both sides and make sure the solder sticks. Then after it cools, dress the slugs smooth.

@AJ/FormS Would you have a picture of that? It would help a long way. (Where it is drilled.)

I debated on the 750 & the 800 Edelbrock AFB carbs I have in top of my 360 with the XR274HR. Right now, it has the 750 up top. Stock jetting as of now. I JUST put it back together W/TF heads. I’m waiting on a RPM - AG to be milled to fit. A Weiand Stealth resides up top for now.