Carter AFB With No Velocity Air Valve

[dieseldazzle]

And if this doesnt work absolutely look at intial and total timing

 

[CBODY67]

Unless the particular car is a CAP (Cleaner Air System) car, no "real" emissions timing setting. On my '66 Newport 383 2bbl, the base timing was 12.5 degrees BTDC. I usually ran it at 15 degrees as we used premium fuel (it clattered on regular from day one!). I could set the idle speed by simply advancing the timing, from the settings at 12.5 degrees BTDC. It was possible to set the idle mixture to the CAP spec 14.2 A/F ratio on this non-CAP carb, but I kept it at the normal "max rpm" idle mixture, or what was later termed "best lean idle".

In setting idle mixtures, the process evolved for a few years after '66. Normally, the procedure was to set it to max rpm for the speed setting at the idle speed screw. Then tweak the idle speed down with that screw, as needed.

Later, once the spec speed was initially set, you adjusted the idle mixture screws for max rpm, but also leaned them until you got a 20rpm drop if any further leanness was attempted, then returned to the prior max rpm. In the first case, you maxed the rpm for the given idle speed screw setting, later, you verified that it wasn't too rich by going a little lean to verify that, too.

Using a vacuum gauge can be problematic, especially IF you try to hit a particular vacuum level at idle. Vac gauges can vary, as the vacuum can also vary with altitude and possibly barometric pressure. Use it as a diagnostic tool, only, which it CAN be very good at on many engines.

As with any diagnosis, the more data points you can collect, the possibly more accurate the diagnosis can be.
CBODY67

 

[70bigblockdodge]

That is a really small carburetor to not have the counterweighted air valve. Except for a 1000 point resto of a museum piece, for drivability and reliability a new carb would be on my radar, if original requires more than a rebuild/freshen up, does not sound like it will. A new carb may have tuning hiccups so it is not a 100% bolt and go. I would seriously look at that distributor based on the lack of continuous use. My 2 cemts FWIW

 

[CBODY67]

On the AFB and AVS carbs, the primary venture cluster has two tubes sticking into the float bowl fuel level, per throttle bore. The smaller one (typically brass) is the idle feed tube. The larger one with the holes in the outer diameter is the emulsion tube. At the top of the venture cluster, there is a small hole that is a drilled orifice, which is a calibration point for the idle feed/mixture fuel.

Inside the bottom of the idle feed tube is another orifice, "idle fuel restriction" or sorts. Another idle fuel calibration point that affect all primary idle fuel. When I was trying to fix a "no idle when hot" issue on my '80 Newport 360 2bbl, I learned about those things, especially that orifice in the lower section of the idle fuel tube!

As long as it was on fast idle, it ran fine. As long as it was in the main system, it ran fine, but when letting the throttle return to idle at highway speeds, the car died. I could put a fine wire into the idle main air bleed and fuel would pour from the venture. The air bleeds "top side" have a direct affect upon fuel mixture! Reducing their open area makes the circuit rich. More area, leaner. With no other calibration point changes!

When I rebuilt the carb, I used spray B-12 to clean things out and test the circuits for flow. All looked good. As soon as the B-12 was pulled out of the idle circuit, the car died. In the Chrysler service manuals, in the AFB or AVS section, I'd found a spec for a "low speed jet" and finally discovered it was the drilled orifice in the bottom of the idle feed tube. Specs varies with later emissions standards, it seemed.

I got a set of small twist drills and set about this new adventure. I first used a bent-wire spark plug gap tool to probe the lower end of the tubes. With each increase in size, first there was resistance, then no resistance as deposits in the holes were removed! Then, I got the twist drill selection and enlarged the internal holes until I "got brass" and stopped. I flushed out the tubes again and reinstalled. With the idle feed fuel restored to prior levels, idle mixture screws worked again.

End result is that with any older carb, there can be some hard deposits inside the fuel feed tubes that might be causing issues. These deposits are not "soft", but "hard" so they have to be removed mechanically as any carb cleaner solvents will not affect them. Sometimes, these deposits are from particular fuel additives/components (as we saw graphically with some of the fuels in the middle 1980s, leaving white crystalline deposits in float bowls and such, necessiatating carb replacement). In more recent times, possibly from ethanol-induced issues.

Just some observations and experiences,
CBODY67

 

[odcics2]

Hmm, trying to remember if this carb has a secondary air valve of some sort... I'll have to take a look tomorrow.

For Sale - NOS Carter AFB

Nope. Doesn't have them! I believe the carb is for a 65 383 4 speed car, going by the number.
Wonder what the reasoning is behind some with secondary air valves and some without. (???)

 

[mcmlvii]

Unless the particular car is a CAP (Cleaner Air System) car, no "real" emissions timing setting. On my '66 Newport 383 2bbl, the base timing was 12.5 degrees BTDC. CBODY67

It's not a CAP car, and I'm not running vacuum advance, strictly mechanical. Initial timing is 12°, total is I think around 35-36°.

That is a really small carburetor to not have the counterweighted air valve. Except for a 1000 point resto of a museum piece, for drivability and reliability a new carb would be on my radar...

Yes I've been thinking that also, a "modern" carb would probably be money well spent. But the distributor hasn't been upgraded yet either. It is the original and still running points. It is probably worn to some degree. All this ancient stuff on the engine is still working remarkably well considering.

Wonder what the reasoning is behind some with secondary air valves and some without. (???)

I'm also curious about the same thing. Very curious. From what I remember in the dark ages, both my '65 Barracuda 273 and '61 300-G 413 carbs had them.

I really appreciate everyone's insight into this issue I'm having. I'm also thinking my bog issue may possibly be exacerbated by the lack of a torque converter in the car. I think for now I'll keep things status quo. Maybe do another rebuild on the carb. Maybe check the timing chain. After I get the reupholstered seats back in.....

 

[70bigblockdodge]

I'm not running vacuum advance

I would get that vacuum advance working again. The fuel mileage alone is worth it, let alone that it will make your engine live longer.
The total advance is okay, but that initial is lower than what I would normally run a 383 at. That is kind of why I mentioned the vacuum guage timing method.
If that is not original carb for your car I would definitely be thinking about a Eddy thunder series 650 cfm

 

[RJRENTON]

Some of the early CAP carbs used pinned idle mixture screws that prevented them ftom being turned out too far and making the mixture rich. Mopar used a propane enrichment system which artificially enriched the mixture with propane gas, introduced thru a constant vacuum connection to achieve a smooth idle, then the idle speed set, then the propane wss removed resulting a lean idle. Then there was the electric retard vacuum advance on the distributor .....what a pain in the ***.....

Set the timing with a vacuum guage. Most carburetor problems are electrical.

Unless the particular car is a CAP (Cleaner Air System) car, no "real" emissions timing setting. On my '66 Newport 383 2bbl, the base timing was 12.5 degrees BTDC. I usually ran it at 15 degrees as we used premium fuel (it clattered on regular from day one!). I could set the idle speed by simply advancing the timing, from the settings at 12.5 degrees BTDC. It was possible to set the idle mixture to the CAP spec 14.2 A/F ratio on this non-CAP carb, but I kept it at the normal "max rpm" idle mixture, or what was later termed "best lean idle".

In setting idle mixtures, the process evolved for a few years after '66. Normally, the procedure was to set it to max rpm for the speed setting at the idle speed screw. Then tweak the idle speed down with that screw, as needed.

Later, once the spec speed was initially set, you adjusted the idle mixture screws for max rpm, but also leaned them until you got a 20rpm drop if any further leanness was attempted, then returned to the prior max rpm. In the first case, you maxed the rpm for the given idle speed screw setting, later, you verified that it wasn't too rich by going a little lean to verify that, too.

Using a vacuum gauge can be problematic, especially IF you try to hit a particular vacuum level at idle. Vac gauges can vary, as the vacuum can also vary with altitude and possibly barometric pressure. Use it as a diagnostic tool, only, which it CAN be very good at on many engines.

As with any diagnosis, the more data points you can collect, the possibly more accurate the diagnosis can be.
CBODY67

 

[CBODY67]

Some of the early CAP carbs used pinned idle mixture screws that prevented them ftom being turned out too far and making the mixture rich. Mopar used a propane enrichment system which artificially enriched the mixture with propane gas, introduced thru a constant vacuum connection to achieve a smooth idle, then the idle speed set, then the propane wss removed resulting a lean idle. Then there was the electric retard vacuum advance on the distributor .....what a pain in the ***.....

The propane method of setting idle mixture was also short-lived with GM, but I don't recall that prior to the earlier '80s? I'll admit that in a "Federal Emissions" area, we didn't see many CAP cars in the middle-60s era. I remember the idle mixture limiter caps that were not supposed to be tampered with, but could be removed for a rebuild. I know that one thing Rochester did in '69 was to decrease the size of the idle mixture holes in the throttle body to limit richness of the idle mixture. This was mentioned in Doug Roe's Rochester Carb book (HP Books, I believe was the publisher).

Respectfully,
CBODY67

 

[70bigblockdodge]

Some of the early CAP carbs used pinned idle mixture screws that prevented them ftom being turned out too far and making the mixture rich. Mopar used a propane enrichment system which artificially enriched the mixture with propane gas, introduced thru a constant vacuum connection to achieve a smooth idle, then the idle speed set, then the propane wss removed resulting a lean idle. Then there was the electric retard vacuum advance on the distributor .....what a pain in the ***.....

Good reason for putting it on a shelf and keeping it with the car as it changes owners. To drive it you need something with more range of adjustment. Stuff like that was put on a car at the time not to make everyone's life easier, so now that the cars have passed into casual use why not make them more user friendly.

 

[CBODY67]

It's not a CAP car, and I'm not running vacuum advance, strictly mechanical. Initial timing is 12°, total is I think around 35-36°.


Yes I've been thinking that also, a "modern" carb would probably be money well spent. But the distributor hasn't been upgraded yet either. It is the original and still running points. It is probably worn to some degree. All this ancient stuff on the engine is still working remarkably well considering.


I'm also curious about the same thing. Very curious. From what I remember in the dark ages, both my '65 Barracuda 273 and '61 300-G 413 carbs had them.

I really appreciate everyone's insight into this issue I'm having. I'm also thinking my bog issue may possibly be exacerbated by the lack of a torque converter in the car. I think for now I'll keep things status quo. Maybe do another rebuild on the carb. Maybe check the timing chain. After I get the reupholstered seats back in.....

The 383 2bbls were spec'd for 12.5 degrees BTDC base timing, which yielded about 36 degrees total advance. The 4bbl 10.0CR motors usually had less base timing and about 31 degrees total advance, as a result. This was allegedly due to the fact that the law enforcement people usually bought gas from the least-expensive place, and it usually was "regular" rather than "premium", on a total fleet basis. Therefore, the reduced total advance helped the engines not clatter themselves to death at WOT on the lower octane fuels.

The vacuum advance definitely needs to be operational. On the '66 Newport, when it went away once, the mpg went to about 10mpg all the time, whereas it usually did an average of about 16mpg (highway and city). More highway than city, though.

If the 300-G 2x4bbl had velocity valves, it was to decrease the total amount of airflow into the engine, so it was not "over-carbureted", especially at lower rpm near-WOT situations (especially as the pre-'71 TorqueFlites did not have part-throttle kickdown. Same with the 273 4bbl (which I believe was unique to that motor, other than metering calibrations).

Remember, too, that all of the carb size charts are built on 100% volumetric efficiency, which only a full-bore naturally-aspirated race engine might attain. Therefore, if you knock it down to about 80% level, you'll get a truer sizing for the engine.

ONE thing about the current Edelbrock "AFB" carbs. They are now more universal-application than OEM specific application. The linkages are not Chrysler-specific, but accommodate Ford and GM linkages, too. The electric choke takes the place of the GM integral choke, Ford "hot water" choke, and the Chrysler divorced choke set-up. So, please do not believe they are "exact fit" for all Chrysler products, or an OEM-exact item for all Chrysler applications. The basic architecture is the same, but it's been "aftermarket-ized" for a wider appeal.

I have an associate in Missouri who runs a carb shop up there. He does not like "the clones" for various reasons. He maintains that the original carb with its original calibrations is the best way to go, even if it takes some rebuilding to make that happen. He is very strong on the original Carter AFBs and has many Carter factory tools to work on them, even to make metering rods. He doesn't like the later Carter AVS carbs either. I hate to ask for specifics in fear he'll blow a gasket. BTAIM.

There are times when a new carb version is a better way to go. Just watch the sales at Summit and such. Last time I checked, after I bought one, the AVS2 650 cfm electric choke was $337.__. I bought a Street Demon when they were under $400.__ a few years ago. Both still in the box awaiting use, along with a few Holleys, too. So, watch for these things!

The distributor bushings probably have some wear on them. They can be replaced, but that'll still leave you with a worn "cam" where the points' rubbinb block rides, which determines each cylinder's actual "dwell" reading, rather than the average reading the meter will yield. Use a dial indicator to set the point gap and you'll see it really easy! Therefore, better to get a new electronic unit. The Mopar Perf kit is a good one and OEM-based. Add an MSD multi-strike control box and you're "done". I found a place to hide the box on my '67 Newport, that was behind the battery and headlights. Extended the harness, used the original voltage regulator (although they said not to, it works well!!!), and other than the two wires going into the distributor body, looks "factory correct". I ran those wires along the firewall to go with the existing electric choke wire for a TQ I used to have on it.

Prior to the Thunder Series AVS coming out, there were many comments at Mopar Nats about "I wish they'd do an AVS, they'd sell a million of them". When they did finally introduce it a year or so later, I wrote and advised that if they'd do a Chrysler-only version in 650 and 750 cfm sizes, they'd have s good market for them. Rather than a "will-fit" Chevy carb. And we see how far that got!

Enjoy!
CBODY67

 

[TxDon]

Good thread, I have a similar AFB on my 66 Monaco 383 and it needs some help. Any recommendations where to get a good quality rebuild kit and new choke diaphragm?

 

[CBODY67]

By this time, most of the kits are somewhat "generic", but a quality name brand can still be important. A KEY thing, to me, is to use an OEM-style base gasket rather than the pressed cardboard gasket found in many rebuild kits. NAPA or Holley's online catalog can be good sources for them. Using the thicker OEM gasket also keeps the divorced choke/carb relationship in the correct orientation.

You'll notice that the Edelbrock AFBs have a "velocity air valve" above the secondary throttle plates. OEM Chrysler AFBs did not have this, which makes them "full manual" secondaries. GM applications used the "air valve" with the counterweights on the ends. It was a trick to get quicker opening of the air valve to grind some weight off of the counterweights, per an old Chevrolet performance book I have (Petersen Publications).

On my '67 Newport 383 4bbl, that's the way it is, NO secondary air valve on the OEM-production AFB. I could floor the throttle off-idle and it would not bog, just move. After I went in and removed the casting flash on the venturis and such (with a point file), making it all smoother, THEN when I floored the throttle at idle, a slight flatness happened. No bog, just a little too much air too soon. I'll take that as a little more total airflow at WOT, which is good. BTAIM.

As I recall, that secondary air valve on the AFBs was a drop-in item of sorts? Which means it could be removed and everything else still work. Which would make it a more accurate Chrysler-spec carb than a Chevy-type AFB adapted to Chrysler applications, with a universal throttle linkage hookup for GM, Ford, and Chrysler uses.

Enjoy!
CBODY67

 

[moper]

Always tune with timing first, then carb settings. Timing affects carb, carb will not affect timing. It sounds like there needs to be a proper timing curve set up, then rebuild the carb and pay attention to the float level...

 

[TxDon]

Does anyone have a good source and part number for a replacement choke pulloff / diaphragm to fit this carb? Also has anyone changed the well type choke to an electric type? If so where did you get and what is the part number?