[mrmark1957]

I need to get more fuel to the idle channel of the Carter 4413S AFB on my 67 400 inch XH motor. Where is the idle channel restiction that I can open up ?

[Kenth]

The amount of fuel to the idle/lowspeed circuit goes thru the idle tubes.
These are the small tubes attached to the venturi cluster.

The amount of idle fuel/air mixture down to the off-idle slots and idle needle holes goes thru the "economizer"/idle channel restrictions.
These restrictions are located behind the idle bypass airbleeds.

[61-63]

FYI I've got AFB dual quad setups on 500 plus cubic inch engines that idle fine that I've done for people and I did not open up the idle jets, air bleeds or anything else in the boosters or the idle openings in the body, so I can't imagine why you would need to open them up for a 400 cubic inch engine. You probably have something else going on. With that said it won't hurt anything if you do open the jets up the engine idling rich isn't going to hurt you as little as the engine sits there idling and you can lean it back down with the mixture screws. Just saying.

[carbking]

Originally Posted by 61-63

FYI I've got AFB dual quad setups on 500 plus cubic inch engines that idle fine that I've done for people and I did not open up the idle jets, air bleeds or anything else in the boosters or the idle openings in the body, so I can't imagine why you would need to open them up for a 400 cubic inch engine. You probably have something else going on. With that said it won't hurt anything if you do open the jets up the engine idling rich isn't going to hurt you as little as the engine sits there idling and you can lean it back down with the mixture screws. Just saying.

Agree.

If the cam is REALLY wild, sometimes necessary to open the idle jets a tad, but have never found it necessary to enlarge AFB idle restrictors.

I also have single AFB's on 455 that idle fine.

Jon

[mrmark1957]

The carbs flat spot off of idle is so bad the engine almost shuts off. I am going to try to increase the fuel flow through the idle circuit before I try another carb. Thanks.

[61-63]

Originally Posted by mrmark1957

The carbs flat spot off of idle is so bad the engine almost shuts off. I am going to try to increase the fuel flow through the idle circuit before I try another carb. Thanks.

Have you checked your float level carefully? The floats are supposed to be high enough that fuel is right on the cusp in the primary boosters so fuel begins to flow through them as soon as they see the signal from the engine as the throttle blades open. If the floats are way low you could experience what you are describing.

[carbking]

The 4413s is one of the carbs with the idle air bleed circuit.

We have found with modern fuel, ethanol or not, these can be challenging with the original idle.

One can defeat this system by drilling the "dimple" on the pump side of the carburetor and then tapping the hole for a "normal" curb idle screw.

We have also found a cause of hesitation, even to the extreme of stalling, is caused by setting the idle TOO RICH, thus creating "puddling" in the intake. When the throttle is opened, the increased intake runner air velocity sweeps the puddles into the cylinders and creates a RICH STALL. This is especially true on engines with automatic transmissions.

Jon.

[mrmark1957]

I have already set the float level, even raised it 1/8 inch higher with no fix of the hesitation. I believe the car is too lean as it runs fine when on choke. I cannot make the engine too rich by backing the mixture screws all the way out. I am going to try to modify the idle circuit for more fuel, then try another carb if need be.

[Kenth]

I would enlarge the .035" idle tubes to .038" and the economizers from .0465" to .052" for starters to compensate for the lower BTU´s in todays fuel.

[mrmark1957]

One of the idle tubes was .031 inch with an .046 economiser. The other idle tube was .035 with a .049 economiser opening. I opened both idle tubes to .041 and both economisers to .052 inch. After I put them back in the carb I noticed one assembly was cast with a 1059 number on it and the other 1060 on the top. Could this have anything to do with the mismatch of sizes. Someone was in this carb before me.The hesitation is better but not gone. Next I want to open the restrictions further. Any Suggestions how big ?

[Kenth]

The choke side venturi cluster is stamped 1059, and the throttle side venturi cluster is stamped 1060.

.041" idle tubes are plenty.
Time to check and verify ignition, vacuum advance and possibly vacuum leaks?

[lust4speed]

Apparently not one of my more coherent days. I'm reading to enlarge the idle fuel opening at the bottom of the tube which makes sense, but when you enlarge the economizer opening are you not also enlarging the air vent side of it which would lean out the mixture? Or does enlarging both sides of the economizer passage simply increase both air flow and fuel flow?

[Sun Tuned]

Mick,
I’m on your side. Haven’t had the need to mess with too many Real Carter AFB’s, seen lots of edelbrock clones that needed help.

I looked at this once and came up with the same conclusion as you.

Wondering about having to tap for a set screw to put the orifice size back after accessing the economiser hole….????

[mrmark1957]

The economiser hole is much smaller that the air bleed that that you access it through. The air bleed hole is about .100 to .125 and the economiser hole is about .046 inch

[25stevem]

If I. Recall right the 9000 series AFB Carbs had a rich stumble / stalling problem where when the Throttle was dropping back to idle a rich enough condition was created where motor would hardly idle, or when opening the throttle again the very rich condition left fuel puddling in the plenum.

I will have to look thru my info later and post it up, but the fix that Carter had was to drill a added hole into the bottom of each Custer at a 45 degree angle to intersect another passage.

[carbking]

Originally Posted by mrmark1957

One of the idle tubes was .031 inch with an .046 economiser. The other idle tube was .035 with a .049 economiser opening. I opened both idle tubes to .041 and both economisers to .052 inch. After I put them back in the carb I noticed one assembly was cast with a 1059 number on it and the other 1060 on the top. Could this have anything to do with the mismatch of sizes. Someone was in this carb before me.The hesitation is better but not gone. Next I want to open the restrictions further. Any Suggestions how big ?

GUESSING:

Since the clusters you have are correct for the carburetor, possibly one was partially clogged with residue from modern fuel. This would explain your idle issues.

Had these passages originally been clean, probably would have had no idle issue.

Oversizing will probably mean turning the idle mixture control screws closer to being seated.

Jon.

[mrmark1957]

Originally Posted by Kenth

The choke side venturi cluster is stamped 1059, and the throttle side venturi cluster is stamped 1060.

.041" idle tubes are plenty.
Time to check and verify ignition, vacuum advance and possibly vacuum leaks?

Idle tubes at .041 and economiser at .055 inch. The throttle blades are at the correct position on the transfer slots. The hesitation is better, almost gone. I would really like to eliminate it completely.The ignition, vac advance and vacuum leaks have all been eliminated as problems.

[Kenth]

1966 Pontiac M/T AFB 4033 uses .040" idle tubes. .052" idle airbleeds, .0571" bypass airbleeds and .0571" economizers.

.0571" economizers may get you where you want to be.

[mrmark1957]

Originally Posted by carbking

GUESSING:

Since the clusters you have are correct for the carburetor, possibly one was partially clogged with residue from modern fuel. This would explain your idle issues.

Had these passages originally been clean, probably would have had no idle issue.

Oversizing will probably mean turning the idle mixture control screws closer to being seated.

Jon.

The first thing I did as a fix was to disassemble the carb, used solvent and compressed air through all parts, reset float level, then re-assembled and still had the hesitation. Then I started to post on here for help.

[mrmark1957]

Originally Posted by carbking

GUESSING:

Since the clusters you have are correct for the carburetor, possibly one was partially clogged with residue from modern fuel. This would explain your idle issues.

Had these passages originally been clean, probably would have had no idle issue.

Oversizing will probably mean turning the idle mixture control screws closer to being seated.

Jon.

Originally Posted by Kenth

1966 Pontiac M/T AFB 4033 uses .040" idle tubes. .052" idle airbleeds, .0571" bypass airbleeds and .0571" economizers.

.0571" economizers may get you where you want to be.

I am at .055 on the economisers now and it is somewhat fixed, for the most part driveable. I am going to the next bigger drill bit at .059 next.