Carter AVS idle issues

[StockMan]

I have a 68' 440 magnum, rebuilt, that has been running well for some time with the smaller AVS carb on it.  I picked up the larger version of the AVS, cleaned it up, added a kit and installed it and made the necessary default adjustments (I.e. air/fuel screws the two turns out, air door, choke, etc).  Oddly enough, now the motor won't idle, it seems that its starving for fuel the way it sounds.  When I pull back on the choke a bit, it comes back to life.  I took the carb off and cleaned it again, with a fine piece of wire through the idle circuit ports, carb cleaner and pressured air, and still, no idle quality.  The throttle blades look nice and straight from one side to the other and I don't appear to have any vacuum leaks either.  I don't know the AVS carb that well, but in the idle circuit there appears to be a needle, no springs or anything, just a needle dropped into a hole (under the primers).  I checked my other carb and its the same so I suppose that wouldn't be a problem.

Any ideas?

[BLK 68 R/T]

Float level? also did you check to make sure the actual idle speed screw is adjusted so the throttle blades are open ever so slightly?

[StockMan]

Thanks for your reply.  Yes, to both suggestions. 
I worked on it tonight again and tried a couple some other parts, the two primary venture clusters, there are 'idle feed restrictors' hidden behind the idle by-pass air bleeds that I thought could have been it but it didn't help.  It seems like it could be running on the left or right bank of cylinders, the way it sounds, but I'm certain there are no blockages.  The throttle blades appear to be centered and are in sync.  I'm sure there aren't any vacuum leaks as well.  I'm at a loss.  I put the smaller carb back on and it runs like a top.  I actually put the larger main jets into the smaller carb and the 440 seems to like the additional fuel.

I'm a bit bummed out that I couldn't get the larger carb to work, I think it will make some difference.

[71 SE3834V]

Did you try turning the air/fuel screws out? When you close the choke it sounds like it pulls fuel through the venturi. Looking at my notes after my 383-4 was rebuilt last fall and adjusting my carb it ended up at L-4 turns out, R-3.5 out to get the leanest, highest rpm at idle. And yeah, make your idle speed screw is in far enough.

[StockMan]

Thanks, I started at 2 turns out and then tried 2 1/2 but that didn't help, I didn't think to go more as it just wasn't running right.  Note that I have the two mixture screws at the base and then one mid-way up in the center.  All three seem to screw into the idle circuit passages (not sure of the purpose of the middle one?).  When I was working on this I set the middle screw to two turns out.  And one other thing that might be a consideration, the carb came with the smaller needles that screw right in so the head are not visible.  I had a set of the other style that I used instead, the ones with the springs that you can turn by hand.  The needle portion appeared to be the same between the two types do I didn't think this would matter.  

Backing the idle/mix screws 'Out' will let in more fuel, correct?

[StockMan]

I pickup up this piece of information from the following source, and I think it could be the cause of my problem.
danscarbs@comcast.net
Dan's Carburetor Service

Carter added a device to the airhorn assembly that introduces additional air when the throttle plates go off idle.  However if you have to open the throttle plates more than normal to get the car to idle then you activate this device. And when this happens more air is added to the idle mixture. Also, as the carburetor gets older the spring looses its tension against the check ball that shuts off this device. When this happens the check ball opens up the passage and allows additional air into the idle circuit. More air means more leanness. 

Dan is referring to the small check ball visible from the underside of the airhorn, over the idle circuit.  Check took a look at my carb and noticed that there is no ball there, the assembly appears to have been removed.  I looked at another carb I have here and see that the ball is visible and spring loaded.
The thing I'm not sure about is where the additional air comes from, the check ball doesn't appear to be blocking any passages that would prevent additional air flow.??

Anyway, gonna try the airhorn that has the checkball intact.

[71 SE3834V]

Sounds like you're on to something.

[StockMan]

Figured it out, previous owner of this carb had removed the aluminum plug just above one of the 'Lower' air fuel screws (this carb has a screw up higher in the middle as well). 
The original plug tapers off to a smaller diameter allowing fuel by into the primary/secondary progression holes, and into the idle feed hole.  The plug used on this carb was just an aluminum plug, same diameter, resulting in no fuel getting through on the one side of the idle circuit.  The plug appears to have been inserted to far in as well, completely blocking the primary/secondary progression holes.  This 'Slot' provides the fuel while the system moves from the idle circuit to the main circuit.  Its anyone's guess why someone would have removed this plug.  I see now that the design of these plugs is very important to the movement of fuel through the idle circuit.

So I'll give this a try now to see how things work.  I still have concerns with the 'Check Ball' that appears to be blocking an air circuit that I mentioned previously.

[StockMan]

Carb works great, but at WOT I ended up with a bit of a ping, and turning back the timing didn't really help that much.  I noticed that the air door wasn't opening smoothly, and there was a bit of bind.
I solved that problem and that appears to have been what was causing the ping (lean condition I think).
My final assessment of this larger AVS carb is that it does add more power over the smaller 630 carb which was expected.  Where I like it is in the mid-range, the 440 seems to like the additional air/fuel and it gets more without having to open up the back barrels.  With the smaller carb it seems to run out of steam at the higher RPMs, until the back barrels open up.  The throttle response doesn't seem to suffer at all, and with the larger carb we use a bit more fuel but I saw that coming.

For the type of driving I do 95% of the time, the smaller carb is better for me, so its nice to have both carbs to swap in/out as needed.  If I ever get to the track I'll throw the larger carb on.  I think for the bone stock 440 magnum, the larger AVS carb is all that is needed, I haven't tried it, but moving up from there I don't think would add anything.