3269 3461 AFB Carter Carburetor

[Duke W.]

Re: 3269 3461 AFB Carter Carburetor

Stu,

I remember in the past I asked a carburetor restorer about these holes I am refering to and he said they are correct for the 3461. The holes are located just under the weight on the secondary air valve and are drilled into the secondary throttle shaft bore, approx (just guessing) 3/32 or 1/8" diameter.

I wish others would post if they have a 1962 or 63 AFB with these holes, it's definitely a filtered air leak as the vacuum travels around the shaft to find air here. When I squirted carburetor cleaner in this area the motor stumbles almost to a stop. If I cover the secondary with a rag tight the car will flood and leave gas visable in the secondary area because this air draw is forced to suck fuel through the secondary inital discharge and booster venturi.

After seeing your pictures of the restricted hot air tube located in the exhaust manifold I did some testing with my car almost blocking the passage but decided it's not my problem. I believe the hot air draw is good for the choke and the operation is normal.


Duke,

To answer your questions, the micture screws at this 6-800 idle speed are 2 1/4 turns each from seated. Vacuum advance is stock 201 tested with miti vac and inital timing @8*, total idle timing is 23*. I have cleaned the primary venturis checking the air, economiser and IFR.

The throttle blades are completely closed, idle screw backed out but the car will not idle below what's stated. If these small secondary holes are supposed to be there I am thinking this is done for the 340 hp to allow more air while maintaining correct primary throttle blade position. As you are aware the 1962 and 63 afb's are duel purpose and the camshafts are very different.

Do you recall these holes in your 3461??

I can't see the holes unless I disassemble the carb, which I don't want to do, but you say they just extend to the secondary throttle shaft bore? That won't create much of an air flow path.

You say the butterflies fit well in the bore, however, I've seen this problem before. The butterflies can be "centered" by slightly loosening the staked screws and slamming the butterflies closed several times. This can be done manually or with a jerry-rigged return spring. This has been an issue with Cosworth Vegas since the two 1.75" throttle bodies are quite large for a two-liter engine.

With the mixture screws out that far, I suspect an air leak. How about the manifold gasket - insulator - shield. Are the insulator surfaces flat?

How about the PCV valve. Is it functionally correct?

Duke

[Timothy B.]

Re: 3269 3461 AFB Carter Carburetor

Duke,

I have driven myself nuts trying to eliminate any vacuum leaks. Intake surface flat, new gasket, plained the phlonic insulator on both sides and trued the bottom surface of the carburetor. There is some damage from the heat groove but it's been filled with JB weld and trued flat, no more problems there.

I also installed throttle shaft bushings in the primary shaft but honestly the carburetor is the same with this idle issue. The only thing that's left is the manifold to head gasket and I don't believe there is a problem here because this carburetor was installed when the engine had the wrong heads and a 1964 afb cast manifold #459 and acted the same way. Since then the correct 461X heads and the mating #349 cast intake manifold both off the same engine are installed.

The PCV is the service AC CV590C and it passes air at idle and it seems to work fine.

Do you think enough air can pass around the secondary throttle shaft to allow a 300hp car to idle at 7-800 with primary blades shut? It may be time to test but I wanted to post first and see what everybody thinks.

[Clem Z.]

Re: 3269 3461 AFB Carter Carburetor

check the PCV system by putting a vacuum guage on the dip stick tube and see if you pull a vacuum in the engine. if not you have air coming into the engine someplace.

[Timothy B.]

Re: 3269 3461 AFB Carter Carburetor

Clem,

I want to be sure I have this straight, idle the car with pcv hooked up and block the air intake where the engine breathes in, on a 63 it's in the front of the air cleaner to the oil fill tube elbow. Check if vacuum is present at the dipstick tube.

I will check it out but I know it will draw a vacuum because at idle if I hold my finger over the air intake elbow at the oil fill tube and let it go I can hear it break a suction and it's fairly loud. Would this tell me the intake manifold gasket to head is sealed?

[Clem Z.]

Re: 3269 3461 AFB Carter Carburetor

Clem,

I want to be sure I have this straight, idle the car with pcv hooked up and block the air intake where the engine breathes in, on a 63 it's in the front of the air cleaner to the oil fill tube elbow. Check if vacuum is present at the dipstick tube.

I will check it out but I know it will draw a vacuum because at idle if I hold my finger over the air intake elbow at the oil fill tube and let it go I can hear it break a suction and it's fairly loud. Would this tell me the intake manifold gasket to head is sealed?

correct it will show if there are any leaks to atmosphere.

[Timothy B.]

Re: 3269 3461 AFB Carter Carburetor

Clem,

Thanks, I will check it out but I think I'm OK here.

I never thought about that test and will run the engine and post vacuum readings before I take this carburetor apart.

I have a hard time believing the secondary throttle bores are wore out allowing to much air from these holes I mention.

[Duke W.]

Re: 3269 3461 AFB Carter Carburetor

Duke,


Do you think enough air can pass around the secondary throttle shaft to allow a 300hp car to idle at 7-800 with primary blades shut? It may be time to test but I wanted to post first and see what everybody thinks.

I don't think so unless the throttle shaft bores are severely worn.

Duke

[John H.]

Re: 3269 3461 AFB Carter Carburetor

FYI there are two small holes on the inside of the Idle mix screws that go through to the bore that are in the 3461 but not on the 3721

[Timothy B.]

Re: 3269 3461 AFB Carter Carburetor

John,

I believe these small holes you are refering to are what's called a vapor vent. They are supposed to be there on the 3461 and they are not present on the 3720-21 carburetors. These holes should be in both primary bores and both secondary bores located ABOVE the throttle blades.

Look at my pics above with the pencil showing the location which I am refering and tell me if your 3461 has small holes here.

[John H.]

Re: 3269 3461 AFB Carter Carburetor

Tim, I am in the process of taking the top of the carb off the body. It has not been apart since I bought the car in the early 80's, so the two haves are a bit of a bear to separate. I do not want to damage anything. If you have any pointers on prying the body haves from the gasket let me know. PB blaster?

[Clem Z.]

Re: 3269 3461 AFB Carter Carburetor

Tim, I am in the process of taking the top of the carb off the body. It has not been apart since I bought the car in the early 80's, so the two haves are a bit of a bear to separate. I do not want to damage anything. If you have any pointers on prying the body haves from the gasket let me know. PB blaster?

make sure you have the screws out that are hidden down inside some cavities

[Timothy B.]

Re: 3269 3461 AFB Carter Carburetor

John,

Make sure you remove the air cleaner hold down screw that's in the middle in addition to what Clem say's.

The lid should come off without any trouble but be very careful..

Clem,

I just ran the car and did the test you recommended blocking off the air intake at the oil fill tube and after approx 45 seconds the vacuum guage reading at the dipstick tube is 3" vacuum.

[Clem Z.]

Re: 3269 3461 AFB Carter Carburetor

John,

Make sure you remove the air cleaner hold down screw that's in the middle in addition to what Clem say's.

The lid should come off without any trouble but be very careful..

Clem,

I just ran the car and did the test you recommended blocking off the air intake at the oil fill tube and after approx 45 seconds the vacuum guage reading at the dipstick tube is 3" vacuum.

as long as you have vacuum reading you are OK as you don't have a big leak. this is why you need a seal on the dipstick so it does not suck dirt into the crankcase

[John H.]

Re: 3269 3461 AFB Carter Carburetor

Tim and Clem, I took the 10 top body screws out( the air cleaner stud seems to be pressed in as I see no threads in the 3721 body) Am I wrong? The top cover does not budge. I have the 1963 shop manual and have downloaded AFB exploded diagrams and cannot find any other fasteners to hold the top body in place. I have worked on other carbs and found "hidden" fasteners in various places , but this is the first time I am working on an AFB. It looks so simple and I am sure that I will kick myself when this thing finally comes apart. I am planing to rebuild it anyway so finding the two ports has become part of the task. - John

[Clem Z.]

Re: 3269 3461 AFB Carter Carburetor

Tim and Clem, I took the 10 top body screws out( the air cleaner stud seems to be pressed in as I see no threads in the 3721 body) Am I wrong? The top cover does not budge. I have the 1963 shop manual and have downloaded AFB exploded diagrams and cannot find any other fasteners to hold the top body in place. I have worked on other carbs and found "hidden" fasteners in various places , but this is the first time I am working on an AFB. It looks so simple and I am sure that I will kick myself when this thing finally comes apart.

the air cleaner stud screws in so soak it down with "kroil" or some good solvent. the stud screws into the main body so there should be clearance in the top for the solvent to get down to the threads