Carter AFB Troubleshooting

Do you know what side the brass insert is suppose to face…toward each other like I have it?
No, they should be to the outside. Not the holes that are pointed to but the brass insert on the end of horizontal part.

AFB Venturies
Carter AFB

I have a 1967 Chrysler Carb that has 2 pins holding the air adjustment screws in I have a broken Air adjustment screw due to someone trying to back out the screw without removing pin, Now I need to remove pin to get broken part out, Have you ever dealt with the pins, do you know what fits them to remove them

First of all it needs to be either heated up or very well lubricated. The pins have a very small Allen head.
I have a 625 cfm Carter and it is idling rough and I can take the left fuel mixture screw all the way out while it is running and no change on the idle or rpm and still idling rough until I push on the throttle just a little and then it will clean up and run smoothly until I let off?

From what you describe I suspect you have a clog somewhere in the idle circuit, on the side you refer to. Take the idle mixture screw out and blow through the hole. They are small and can easily get clogged. From there find the passage way going to the idle mixture screw. Use thin wire to clean it out if you can. While you are at it inspect the screw for any grooves.

You didn’t mention if you rebuilt the carburetor. That would be a good place to start if you haven’t already.
Can I use the pointed check weight above the check ball?

Do not put the pointed check weight with the check ball. If it even fit, it would be too heavy and you would get a hesitation when throttling up.

A check ball would have a small weight, or spring above it. The pointed check weight is used without a check ball. The AFB came either way. You can also try using a check ball above the 1st check ball. This is usually enough weight.

Test by putting fluid in the accelerator pump well. Hold down either the check ball system, or the check weight system with a brass drift punch. Push the accelerator pump down the well. You should feel a bit of pressure and little if any fluid will come out of the main discharge.

If you get no pressure, then try the other setup (check ball, or pointed check weight). If still no pressure use a brass drift punch against the check ball, or weight and tap a few time to seat it.

Carter AFB Floats

Bogs down when I floor the pedal.
Does it have a choke, it’s possible the choke may not open all the way not allowing the secondary’s to open properly, also the passage’s in the secondary cluster’s are they clear, need to make sure there not clogged. Could be lots of things, needs to check compression also.

No FuelI rebuilt a Carter AFB Performance Plus carb and it ran fine for about 3 weeks. Then it would not start unless you primed it by spraying fuel into it and cranking the engine for awhile. Then it would start and run, but the next day no good and had to repeat process. Replace fuel filter and we get a very good stream of fuel when cranking from the hose between pump and carb.
Do you have and suggestions on what to do.

Could be a lot of things.

Plugged fuel filter.Needle & seat sticking.
Float sticking.
Low fuel pump pressure.
It is possible that the fuel is running back toward the fuel pump when you turn it off. That would be the needle & seat.Make sure the fuel tank vent is open. Some have an extra vent tube and some vent via the gas cap.Could be percolating – engine gets hot, turn the engine off and fuel boils and evaporates. 

My secondary jets have no acceleration tubes or any other plumbing underneath. Is this normal?Yes, it is on some. Not all have tubes.

This is a problem that one of our customers reported to us along with the email conversations.Sorry to bother you. I bought kit 4011 for my 1958 Cadillac Eldoradro, Carter 2862S AFB carb. Can’t get car to come off idle, wants to die. Warm, choke off. Idles O.K., 500-850 RPM O.K. But when I push the accelerator to increase the RPM’s avove 850, it wants to die. If I coax it past this spot, at higher RPM’s it seems fine. A stream of fuel comes out the two accelerator pump jet nozzles when I depress the throttle, so I think the accelerator pump is O.K. I’ve adjusted the two mixture screws. There is a big air adjustment screw located between the two idle mixture screws, I tried to adjust that also. (But I don’t actually know the procedure for this air adjusment) Once it starts getting past the stumble, I notice drops of fuel coming out of the primary venturi’s, and dropping down onto the throttle buterflies. (I would think it would be atomized, not drops?) I’ve disassembled the carb a couple times, the float bowls are about 1/2 full. I’m stumped, I didn’t have this problem before I rebuilt the carb. I didn’t remove any shafts or butterflies. I would appreciate any ideas you have to offer. Second update: I should have checked this before I sent My first e-mail. My problem is a lean condition. If I pour a lttle gas down the carb while it is stumbling, it stops stumbling and smooths out. So the question is: What causes a just above idle lean condition? Third update: I fully closed the big air adjustment screw located between the two idle mixture screws, and this helped alot. I moved the accelerator pump rod down to the bottom hole, and this seemed to help some. I stll have an off-idle stumble, but it’s driveable, it doesn’t try to stall, just stumbles. The stumble is smooth slow acceleration, not punching it.
SolutionI took it apart again, and found a piece of debris partially plugging the small brass tube feeding fuel to the primary venturi, (the small tube inside the bigger tube with holes in it) The clue was, just above idle fuel would drip out of one venturi, (the bad side) No more hesitation, and I was able to open the air adjustment screw to set the idle speed.

Dual set up running rich and secondary problem.No ID on these carbs but I believe they came off an early 60’s Pontiac. Dual AFB’s on Weiand manifold on a 1957 Chrysler 392 Hemi, probably the 325 hp model.
Engine runs fine but when I recently pulled the plugs they are all black, rich. I was thinking if I could put smaller primaries in that would help the rich mixture.
After reading your info on your website I went out and pulled the metering jet and the primary and secondary jets. The primary jet measures 0.090, the metering rod is about 0.080 in the middle and 0.060 on the end. The secondaries are about 0.070 for what it’s worth.

Maybe one other question while I’ve got your attention. See if what I see makes sense. First there are no chokes. The rear carb is primary and as the throttle begins to open at about half throttle the forward (secondary carb) linkage begins to open. I’m assuming the rear (primary carb) secondaries will begin to open from vacuum at that point. Then at about 3/4 throttle the vacuum secondaries on the front (secondary carb) begin to open as well. I don’t know of a way to confirm the action of the vacuum secondaries. Does that sound right?

I believe that if there are no chokes that these are off a Chrysler. As for it being rich that could be that they may have been sitting for too long or the floats are sticking, could be a lot of reasons. I would think Sirius about leaning them down. As for the secondary’s they are both mechanical and vacuum operated and it is a progressive type linkage.

Taller jets

My AFB has taller jets than those currently available, is this an issue?

No, you can use the standard replacement jets, just be sure the orifice size is the same.

What is the vent pointed to in the illustration.

AFB TroubleshootingThis is the fuel bowl vent. This would have been connected back to the engine so that the gas fumes were burned off. Prior to this carburetors were vented to the outside air. It must be left open, or gas will get siphoned from the flow bowl when you don’t want it to.

When I disassembled there was no check ball in accelerator pump circuit, only the brass weight under the discharge nozzle assy
If the check weight has a pointed end, then it acts as a check ball and weight. No ball is necessary.

There is no check ball in the bottom of my accelerator pump well.
Your AFB probably has a check valve near the bottom of the float bowl next to the pump well. This is the inlet check.

When I pump the accelerator the main discharge doesn’t spray until the throttle is partially opened.
One common problem often overlooked is the electrical system. The distributor advance in particular. Make sure it is operating as it should.
A list of possible problems (not in any order):

  • Not enough fuel in the pump well. If the intake check isn’t working as it should it may not be filling in the well. There is an inlet check in the bottom of the float bowl and it has a check ball in it. Take it out and make sure the check ball rattles around.
  • The accelerator pump cup rolled up when being installed. A pump should be twisted in a circle while putting it in the well so it doesn’t curl up.
  • Pump cup has been damaged by ethanol, or some other chemical that is in the gas. We recommend using Ethanol Defender.
  • The wrong accelerator pump was installed. The carburetor kit should be matched up with the carburetor number to insure it is the correct pump.
  • The linkage going to the accelerator pump is loose, or perhaps bent so that it doesn’t push the pump down right away. Operate the linkage and watch the pump action closely.
  • The accelerator pump circuit is partially plugged and gas gets through only with maximum pressure.

There are many reasons your carburetor is flooding. Flooding means fuel is overflowing over the top of the carburetor. Running rich means the exhaust has black smoke, or there is a strong smell of gas.


  • Test your fuel pump. New fuel pumps are especially troublesome. Check your motors manual for the proper pressure, but for the AFB it should be around 5 lbs. Too much pressure will cause the needle not to shut off the gas.
  • The needle & seat may be damaged. If while adjusting the float, pressure was put on the needle then it could easily have damaged the viton tip. If the needle is new, wipe the viton tip with mineral spirits to wipe off the black residue. Turn the top upside down and while the floats have the needles closed, blow into the fuel inlet (not too hard). Air should not get through.
  • Make sure there is a gasket under the seat and there is only 1 gasket. We have seen old gaskets left behind, then a new one added on.
  • Test your floats for leaks. Heat up some water and immerse the float. Bubbles would indicate a bad float.
  • Check the float level.
  • Your floats should be centered in the float bowls.
  • Make sure there is clearance on each side of the float tangs.
  • Move the float up and down to feel for any resistance, or catching.
AFB Flooding
  • There may be dirt getting into the needle & seat holding the needle open. Filters may be dirty, or perhaps the fuel tank is dirty.

Flooding can be summed up with one idea. Too much fuel is getting into the float bowl.

Running rich after rebuild

  • Since it was running OK before we can rule out the metering rods and main jets. 
  • Make sure the passages from the idle mixture hole and the off idle above it go all the way through the venturi’s. The small holes on top of the venturi is what you are looking for. Look at the off idle video to gain some knowledge on how that works. 
  • If the carburetor was sitting for many months, or years I would highly suspect a plugged passage. Look at every hole you can find and test by blowing air through the hole.
  • Look down the carburetor at idle. Do you see fuel dribbling out of the venturi. If so, then that is probably the problem. The main discharge may be leaking. There will be a check weight in the discharge hole (with pointed end), or perhaps a check ball and a spring above that. Depends on the vintage of the AFB. Take the carburetor off and test the accelerator pump circuit. The small holes on the venturi can get plugged easily.
  • It isn’t unusual for the venturi gaskets to need to be trimmed a bit so they sit flat. If they don’t sit flat fuel will leak into the bore.
  • Test the needle & seat. It is possible that while adjusting the floats pressure was put on the viton tip damaging it. It isn’t unusual to get dirt into the needle & seat after rebuilding.
  • Be sure the floats are centered. Move them up and down to feel any catching.

As with flooding, too much fuel is getting into the float bowl, or extra gas is getting siphoned into the bore because of a plugged air vent.

Not Idling Well & Center Mixture Screw Doesn’t Make a Difference.
Not all AFB have the center adjusting screw.
Well the fact that it does the same thing with 2 different carbs tells me to look at electrical 1st.Compression test might reveal 1 or more low cylinders which will cause an idle problem for sure.
I wouldn’t discount a vacuum leak that hasn’t been found yet.
The center screw not making a diff is worrisome. That smells of a vacuum leak to me.
Double check the mounting gasket to be sure it isn’t leaving some port exposed causing a leak.
Spray carb cleaner around all vacuum sources and mounting gasket. A change in rpm tells you that you found the problem.

Runs Lean at High End, or Lack of Power

Look at the plugs. Tan, or brown is good. White, or near white is too lean.

  • Check float level
  • Test the fuel pump. It might be on the weak side.
  • If the engine has been sitting for months then the gas has probably coated the inside of the carburetor with varnish restricting flow.
  • Jet size – You need to think about this. Jets just don’t change that fast. Now if you just replaced the carburetor, then the jets and/or metering rods may need to be changed. If you have been driving with this carburetor, then changing jet size is just covering up some other problem.
  • If you think you need to change jets, or metering rods, try the metering rod 1st. They are easy to change (be sure to put a rag down the carb throat), and the carburetor can be mounted on the car. Measure the existing rod and then pick a rod that has a smaller power size.
  • The carburetor may just be dirty with restricted passages. A cleaning/rebuilding would be in order.


Updated on 04/05/2022

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