Carter AFB fast idle cam position trouble

I'm setting up my Carter AFB and I can't seem to get the fast idle cam set right.

No matter what I do, I can't get the index mark on the fast idle cam to line up with the screw. Even with the rod disconnected, it won't rotate far enough. The lug on the right side of the fast idle cam rides under the lug of the middle piece (to which the rod is connected) and it in turn is held back by the lock out arm. Does that make sense? I can't see how to make it work.

Can anyone see what I'm missing here? I think I have it connected according to the manual. I've got the fast idle cam spring riding on the upper lug, so it's under tension. I've set the choke and pump by the manual.

Could the parts behind the fast idle cam be stacked incorrectly? In the third picture, the green lug is preventing the red arm from rotating up, so I can't get the index mark where it belongs.

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My fast idle cam lug is under the lug of the second plate.

The black and white picture of from a 1966 Pontiac Carter AFB manual and it appears to show the fast idle cam on top of that lug, although it's hard to see in such a grainy picture.

Could my parts be out of place?

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The screw has been removed before from damage in the slot. So, maybe they put it together wrong. What would happen if you moved the bottom of the red linkage above the green lug or maybe the blue lug above the red linkage? I think the second actually. Look at how the spring is in your Pontiac picture.
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> The screw has been removed before from damage in the slot. So, maybe they put it together wrong.

That's what I'm thinking.

The reason the carburetor is off is because the shafts were leaking and I sent the carburetor out to have the shafts bushed. I think the carburetor was photographed before disassembly and put back the way it was found, or these items were never taken off the shaft. The reason I think this is because the fast idle cam rod, which was not sent, was the right length to connect it in this position. So someone, at some point, may have gotten these in the wrong position.

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> maybe the blue lug above the red linkage? I think the second actually. Look at how the spring is in your Pontiac picture.

I'm also thinking the blue lug above the red as well.

I think the spring in the Pontiac picture is the clearest evidence that mine has been set incorrectly.

I wish I could find a clear reference picture online that shows a close up of this sub assembly. The original manual doesn't seem to have anything.

Does that big flat screw just sit in the side of the carburetor? Can I just back it out and swap the bits around?

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Here are some photos from the '66 Pontiac Tempest shop manual. Fig. 6B-98 looks the same as the grainy image you found. This one shows the trip lever (red) and lockout lever (green) are installed correctly.

The fast idle cam (blue) needs to be removed and rotated CCW and reinstalled so that the spring can relax and hug the projection on the trip lever. In this position the upper foot of the fast idle cam is free and does not touch anything else.

Fig. 6B-91 shows the individual pieces. The retaining screw appears straightforward and just threads into the boss on the carb body.


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Thank you so much, this is exactly what I've been trying to find. I think I'm about to fix a lifetime of difficult cold starts...

Why did the Pontiac division deem this image to be manual worthy but not Buick?

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If you look at your pic. where you have the Red & Blue lines the little hair spring is in the wrong spot. All you have to do is loosen the screw, not remove it, it will give you enough clearance to move the spring up to catch the small tang where the upper part of the spring rides against.
Hopefully I've explained it properly to be understood.
I rebuild carbs. for people all over the world with AFB's being my primary/main carbs. I rebuild. I have three dual quad 2x4 units now that I'm doing along with distributor rebuilds, recurves & installing electronic conversions.

Tom T.
Dr. Frankenbuick

Thanks for the picture, I think mine looks like that now. With the choke closed the fast idle cam doesn't rest on the trip lever but it does when it's open. I hope that is okay.


You've helped me before and your reputation precedes you. Does my new photo look right to you?

I've moved on to the next step, adjusting throttle opening. I've noticed that the secondary throttle valves open to almost vertical if I snap the throttle open but they only open part way, or not at all, if I open the throttle slowly. Is this common? It seems like the secondary shaft is a bit stiff. What do you make of this and how to fix? I did have the shafts bushed, as they were leaking fuel.

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It looks like I've got it all assembled and ready to go on the car. Only a few more questions...

Does the vacuum port at the back (pictured) have a gasket or any sort of sealant? There was no gasket in the kit and none when I took it apart. It also doesn't thread in very far before it stops; is the hole tapered?

There are two small exposed screw hole ends pointing down in the front of the carburetor (second picture). I hope nothing is supposed to be showing through those...

So excited to almost be ready to get this on the car!

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IF fuel was leaking from the throttle bores the float level was way too high or the carb. was flooding open from a bad needle & seat or dirt or a variety of other things.
That hookup for the rear is for the power brake booster vacuum supply hose. It's a NPT thread. No sealer or gasket or anything. Just tighten & it will seal itself, BUT not so tight that it will twist off/break, and yes the hole is tapered.
Correct, nothing goes into those holes they are for retaining the top of the carb. to the body.
If you look at pic. 68-91 you will see the throttle shaft, secondary side, lock out plate. It prevents the secondarys from opening when the engine is cold. IF the secondary side is not opening the throttle adjustment isn't opening all the way or something is preventing it from doing so. Could also be the bushings were drilled not in line which will cause a bind. You may have to remove the thottle blades & use a 5/16ths. reamer through the bushings for a better fit.

Tom T.
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I'm sure my shafts were drilled straight. It was done by a well experienced carburetor guy, highly recommended expert in his field.

A couple of small shots of lubricant seem to have loosened up the secondary shaft quite well. I'm sure with a little break in time on the car and all will be well.

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New Member
Greetings, I figured this was the best place to post this.

I have a 66 Pontiac Bonneville 389 with the AFB. This carb was rebuilt by a shop and worked perfectly for a few years...until it suddenly developed two problems.

It has two issues:
1- when cold, the fast-idle cam does not rotate far enough clockwise to put the set screw on the highest step on the cam. I have tried bending the pushrod from the choke plate to shorten it, but that doesn’t work and seems to throw off the choke plate position., even though that is goverened by the thermal choke... I had bent this rod at least 30-degrees, which seems wrong...looking at the diagrams and photos above, it appears to be assembled correctly. The choke is the factory thermal, which is operating properly and not binding (for now). Is there some other adjustment I’m missing?

2- Shortly after this rebuilt carb was installed: when parked after a drive, fuel seeps out around the accelerator pump shaft, reeking up my garage and leaving a perpetual varnish stain on that corner of the carburetor. There is no seal for the top of the car
Not an AFB expert but...

Post a picture of the fast idle cam assembly if you can but it should rotate counter clockwise to get to the highest step/fastest idle. If it worked before and now doesn't, I would suspect the choke spring has become weak and might not be putting out enough tension to fully rotate the fast idle cam. Does it improve if you set the choke for a richer idle?

For the leaking pump my only thought is a bad seal on the pump gasket.

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Also, does your intake manifold have an exhaust cross over like a Nailhead? If so, are you sure you have the right carburetor base gasket? And the steel plate on top of it?

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New Member
The intake does not have an exhaust crossover. I have not removed the carb since these problems started; it's been on about seven years since it was rebuilt. *Until about a year ago, it worked perfectly: floor the pedal once, start the car, fast idle, 10-seconds, blip the gas, throttle comes down, then one more blip in a minute & it;s all good.

Now, unless I manually get in there and set the cam up on the step,. it barely idles and god knows what kind of crap is building up in there until it warms some because I have to hold the pedal down to simulate a fast idle. If I drive off too quickly when cold, I get an open-choke condition where it dies when I give it gas until it warms up.

The accelerator pump does not have a top gasket; I've rebuilt AFBs before myself, and none of the kits come with upper gaskets for the accelerator pump plunger shaft or any space to attach one to the underside of the top cover.

The car has not been started in a week. These photos were taken after I pulled the throttle back to set the choke. I did pop off the throttle rod for visibility. This is the position that the fast-idle cam rotates to:


Here's the setup. The only thing I've changed out is the pushrod - I removed the one I had bent & substituted an unmolested one from one of my stock of AFBs. Bending it did nothing except screw up the position of the throttle plate vs. the butterflies, as far as I could tell.


And here is the choke plate setting. It doesn't snap to this position, it is somewhat leisurely in its travel, but it gets there. The counterweight piston is probably getting gummed up again...


You can see the crud building up around the accelerator pump. One would think that some type of bung seal would fit there - but I've never seen one. It reeks pretty good after parking it.

Thanks for your responses.
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Active Member
Thanks for all those pics and the explanations. I've fixed mine so that it now looks right. But I discovered after hard starting for a few weeks that there was nothing inside the auto- choke housing! I bought an electric one and hooked it up. Now I'm having a problem with the high idle cam snapping into place on cold start. The only way I've been able to get it to work is to crank the choke adjustment all the way around, well past the marks. Then it seems to have enough tension for things to work. I haven't rebuilt a carb in 25 years, so what am I missing?


New Member
OK once she's dead cold, open the throttle all the way, once, and let go. That should set the choke in the cold/closed position. Since you've been adjusting the choke, open the throttle or block it open. Just a bit is fine, you want to be sure the fast-idle screw isn't contacting the cam. Then rotate the choke so the choke plate opens. Rotate it back so that it is just closed. Then tighten the set screws for the choke.

On the driver's side, see where the cam is. Note the position of the rear link to the choke plate, then note the cam. If the fast-idle screw isn't over the highest step, then you need to bend either or both of the little tangs towards each other until it is.