Originally written July 2010
Updated April 8, 2011
!! --- This page is not yet complete --- !!
This is a how-to guide for rebuilding the Carter BBD carburetor found in Jeep CJs, early Jeep Wranglers, and other AMC vehicles from this era.
The BBD is thought to be junk by many people because it is complex, difficult to service, and the idle tubes are easily clogged. When you consider that the 1983 and later BBDs have the added complexity of the computer-controlled stepper motor, then things only get worse.The BBD can be made to run right as long it is in generally good condition and you understand all of the factors involved in making an engine run well. Any carburetor is only one piece of a complex series of systems required for an engine to run.
If you have never rebuilt a carburetor before, you must understand that the BBD is not thought to be easy to rebuild. It is truly a puzzle because the pieces can fit together correctly only one way. This guide will share the knowledge I have learned by rebuilding the Carter BBD.
Table of Contents
These links take you directly to some of the main sections of this guide.
Assumptions, prerequisites, and general information
Notes about this page
This guide includes large, 800 pixel wide photos to help illustrate the details of some of the small parts. In many of the photos, you will see a screwdriver, awl, or fingers pointing to the critical element in that shot. Remember that a photo will always follow the text. In other words, if you are reading something, it is describing something in the photo that is below the text.
Before considering a rebuild
Before spending too much time or money on your Carter BBD, there is one important thing to check. If the main shaft going through the Throttle Body Assembly has too much play in it, then your BBD might be loss. The aluminum body will be worn away by the continual motion of the steel shaft as the driver moves the accelerator pedal and the return springs pull the throttle closed again. If enough aluminum has worn away, then the shaft will become loose and you'll have a vaccum leak that will cause idle problems. A machine shop might be able to repair this by drilling out the shaft holes and installing bushings, but most people will consider the BBD a complete loss at this point and either replace it with another BBD or a totally different carburetor.
Here's the throttle body aassembly to show the part in question. If the metal shaft running through the whole assembly wobbles around, then it could be a problem:
An additional consideration before rebuilding is to procure 2 or 3 other similar BBDs from other Jeep CJs. Because many people trash their BBD in favor of another brand of carburetor (Weber, Motorcraft), BBDs can often be had on Ebay or Craigslist for cheap or free. Having a fully-assembled BBD on your table to look at while you rebuild yours can be very helpful. If you lose a part (like a spring) or need a part in better condition, having a couple of carburetors of spare parts is good.
The book The Jeep CJ Rebuilder's Manual by Moses Ludel has several pages on servicing the Carter BBD, but like the rest of the book, the information is not complete and does not serve as a complete step-by-step, 'how-to' guide for a first-time rebuilder. The information there is better suited for someone who is already an experienced mechanic who has rebuilt carburetors before.
Carter BBD Rebuild Procedure
You will need the following items to complete the rebuild
- Rebuild kit for your specific model Carter BBD
- 1 gallon can of carburetor cleaner, or spray cans of carburetor cleaner
- Old toothbrush
- Compressed air (compressor & tank, canned air, or your breath)
- Big supply of paper towels
- Assorted common hand tools
- Shallow trays, container or bags to hold small parts
- A place to disassemble and clean the carburetor
- A big, clean, well-lit place to assemble the cleaned parts
- Plenty of time
This guide will use the following diagram from my rebuild kit. This will ensure that each part is referred to by a common name and number.
- .032" drill bit and electric drill to turn it
- Ultra-fine steel wool
(Insert exploded view of carb)
This procedure also assumes you have removed the carburetor from the Jeep by removing the 4 hex head nuts that secure it to the intake manifold.
If is very easy to lose the smaller parts of the carburetor, so be careful and work slowly. In my experience these BBD rebuild kits do not come with springs so do not lose those.
Step 1 - Disassembly
I will not cover disassembly in detail. It is perhaps easier to list the items that you may not want to disassemble.
Save old gaskets (especially large ones) as that can sometime help determine how to orient the new ones, or show you which gaskets you don't need from the rebuilt kit because the kit may include several extra gaskets. (assuming the carb was built correctly the last time.
(insert photos of items not to disassemble: throttle body, automatic choke, stepper motor)
Step 2 - Cleaning
Scrape any remaining gasket material from all surfaces. Be gentle with the carburetor pieces as some of them are aluminum. Set aside all non-metal pieces or other pieces that should not be put into the cleaning bucket. Small items like BBs and small screws are easily lost and are better left out of the cleaning solution.
Put the remaining small parts into the basket and put that into the can of carb cleaner. Then put in 1 or 2 of the remaining large pieces. Let everthing soak for an hour or two. After soaking, remove each piece and use a toothbrush to scrub areas still caked with deposits. Wear gloves and eye protection. You may need 2 or 3 sessions to get everything soaked. Do not soak the gold-colored large pieces overnight, as this will start to remove the gold-colored finish. I don't think that removing the gold finish is harmful though.
Use paper towels to remove the cleaning solution and remaining grunge from each piece. Put cleaned pieces into shallow containers to keep them from being lost.
After cleaning, parts with fine passages should be blown out with compressed air. You can also inspect some passages visually to see if you can see light through them.
You can use ultra-fine steel wool to polish pieces that might benefit from being polished, such as shafts or the outsides of the larger components that are visible when the carb is installed. Be very careful with the steel wool because it tends to leave a trail of steel fibers wherever you use it, so do not put it near your rebuild area. Use the steel wool in a place where it will not comtaminate the newly rebuilt carburetor. Use it over a large, empty trash can or some other place where you can easily locate a piece if you drop anything.
Step 3 - The rebuild kit
You need to purchase a rebuild kit that is suited for your specific Carter BBD. There are many different sub-models of BBD, and yours will have a triangular-shaped metal tag with a number stamped in it. The tags are thin metal, break off easily, and are fastened to the carb using one of the long screws on the back side of the carb. Common numbers are the 8383 and 8384.
Here are some examples of tags:
The rebuild kit may contain parts that you will not use. A given kit may be designed for other variants of the same carburetor, so don't worry if you have parts left over unless the parts are shows in the diagram. Here's a photo of the opened kit and its contents:
Closeup of the part number:
The kit comes with a 4 page instruction sheet. The main problem with the sheet is that the direcitons for adjusting the carb are vague and difficult to understand if you've never worked witha carb like this before.
The following image shows a ruler that is included with the kit. Note that the English scale is in 1/32" increments. This is used for making measurements during adjustment.
Step 4 - Drilling the idle tubes
This step (Drilling the idle tubes) is not mandatory. You might take the time to research on your own to see if this is something you want to do for your particular situation.
Terry Howe's Jeepteck.com
Adventures under the Hood
The Carter BBD idle tubes are known to be easily clogged. Clogged tubes can cause idle problems. One workaround for this problem is to enlarge them slightly by drilling them out with a .032" drill bit. Note that if the tubes are 100% clean and not-clogged, drilling them will not increase performance or fix immediate problems. Drilling them simply makes them less prone to being clogged down the road by contaminents such as debris from the fuel tank or fibers from the fuel filter.
Here you see the Tube assembly and .032" drill bit. The penny is shown for size comparison.
Here is my vintage Dremel Moto-tool which worked well to turn such a small bit.
To perform the procedure, I positioned the drill on its side to steady it, put the tip of the drill bit on the end of the tube, and then started the motor. The bit cut the brass material very easily. After drilling, use compressed air to blow out the tube to remove any metal shavings.
Step 5 - Venturi cluster
The venturi are the heart of any carburetor and the BBD is no different. Because the BBD is a two barrel carb, it has two venturi. Due to the way they are imbedded in the body of the carb, it makes sense to assemble them first.
Here we see the components needed for this step. Note that I left out the small steel ball from the photo, but you will need the small steel ball, and not the large one. Also note the differences in the gaskets: One is flipping the finger, and the other one looks like a crown.
Here is the bowl piece where the venturi cluster will be installed. The two inside surfces that look warped or dimpled are really not. The reflected light does strange things there:
Next, we see the small steel ball after it was inserted into the correct hole in the larger bowl piece. Note this is the SMALL ball and NOT the large ball!
Here, the correct gasket is positioned in place:
The venturi cluster piece is set on top:
Now the idle tube assembly is set in place.
You might find it difficult to push the tubes into the holes in the gaskets. If this is the case, remove everything (except the ball) and assemble the parts in your hands, and then set the assembly back onto the carb bowl.
Finally, find the two screws for the venturi cluster. These screws have passages in them. Make sure they're clean before installing back into the cluster:
Lastly, we see the two screws in place:
Step 6 - Attach throttle body
Next, the bowl piece is attached to the throttle body. Here are the parts we need:
Be careful to get the correct gasket, and be sure to orient the gasket correctly. This photo shows the lobe of the gasket to look for. Orient the gasket so this lobe aligns with the correct hole:
(Note that this throttle body has a piece broken off near one of the idle mix screws)
Put your two screws in from the bottom of the throttle plate:
Place the bowl on top and lightly tighten, but remember that you're screwing steel screws into an aluminum part, so don't get them overly tight or the aluminum could be damaged. You will notice how the bowl overhangs the front of the throttle body where the idle mix screws are located. We also see the threads where the brass fuel inlet fitting will be installed. These are all on the front of the completed carb:
This shows the two screws from the bottom side of the assembled unit:
Step 7 - Install float
Next we install the float and the fuel inlet valve, which the float opens or closes. Here are the needed parts. Note that the retainer clip is not shown in the photo. It is a U-shaped piece of metal:
Here is a photo of the float pin retainer:
First, position the float with the correct side up and put the pin in the holes, as shown here:
Next, put the float into the bowl, with the correct side up, letting the pin slide into the grooves:
Here we see a second image of the pin in the grooves:
This is the fuel inlet valve which you should get new in the rebuild kit. The pin is inserted into the valve in the same orientation shown here. The brass pin has a rubber tip which goes into the hole:
The fitting is then screwed into the bowl:
The point of the float is to maintain a consistent fuel level in the carburetor, and it works just like a toilet tank with a float: the liquid level drops, the float drops, and that opens a valve to let in more liquid.
This photo shows the installed valve. The float and valve work together: Gasoline is pushed by the fuel pump though the fuel line, through this valve. As gasoline enters through the valve, it fills the bowl. As the bowl fills, the float rises. At some point, the float rises enough and it pushes on the rubber-tipped brass pin. When the pin seats fully, this shuts off the flow of gas entering the brass fitting. After the engine has consumed fuel, the gas level in the bowl drops, the float drops, and this causes the valve to open which allows more fuel into the bowl. The float must be adjusted to the correct level for the carburetor to operate correctly. This adjustment is done in the next step.
This piece is very important. This clip holds the float rod in place. It slides into the same groove the rod does:
Here we see the top of the clip after it has been fully seated:
Step 8 - Float adjustment
Find the ruler and the instruction sheet that came with the rebuild kit. On the instruction sheet, locate the figure that states the float height. In my kit, the height is 1/4". This means that the highest part of the float must be 1/4" from the top of the bowl.
The trick to adjusting the float is that the float must be in the up position when you measure it. You can either do this by holding the carb upside down, or pushing the float lever against the brass valve pin, which causes the float to lift up. The measurement is taken from the highest part of the float.
First, practice putting the ruler on the highest part of the bowl, like this:
To adjust the float height, you simply bend this piece (shown by red arrow) backward or forward as needed. Note that the brass fuel inliet valve and U-shaped clip have been removed for clarity, but you do these installed when you make this adjustment:
If your float level is too high, then you need to increase your measurement, so you need to bend the piece back, away from the fuel inlet valve.
If your your float level is too low, then need to decrease your measurement, so need to bend the piece forward, toward the fuel inlet valve.
It will take some time get the adjustment correct becuase you're dealing with small fractions of an inch. Here, we see the float has been adjusted to 12/32" (.375") which is not 1/4" (.25"). Here, the height has not been adjusted correctly yet.
Step 9 - Pump Assembly
This step is difficult because you have to hold a shaft down under pressure of the spring, and then slide a small metal pin into the hole in the shaft. It would be easier if you had 4 hands. The key to completing this successfully is preparing the parts and knowing what position things need to be in before you start assembly.
Here we see the metal Pump Link and the Pump Link Arm. Set them up as shown here before assembling them:
Insert the arm into the plastic link piece:
Next, find the new Pump Assmembly in the rebuild kit, and the Pump Spring:
Insert the Pump into the large Bowl Cover Assembly piece:
Here you see the shaft of the pump sticking up through the hole:
Take the Pump Link you assembled earlier, and stick the metal shaft into the hole in the Pump Shaft, shown here. You'll have to use one hand to press the pump up, to compress the spring:
Next, find the Piston Assembly and the Metering Rods. Insert the rods into the Piston Assembly as show in the next two photos:
Now, stick the Piston and Rod assembly into this hole in the Bowl Cover:
It should slide down to the bottom like this:
Next find the Pump Shaft. This photo shows the end of the shaft already installed. Yours won't be installed, but you're about to install it!
The Pump Shaft is the large metal rod with a cam/lobe attached to the end. Slide it into the Bowl Cover. While you're sliding it in, it must slide through the green plastic Metering Rod Arm and the Pump Link that you've already installed. The following photo shows the assembled pieces.
Also note in the following diagram where the awl is pointing: The small lobe on the green piece, must sit under the Piston Assembly.
This photo also shows the assembly. The awl is pointing to one of the two holes where a screw will be placed. You need to adjust things so that you can see both holes in the shaft.
The following photo shows 2 important things
First, we see the awl pointing to the bowl vent lever, which needs to sit above the plastic Pump Link Arm. The reason for this is that the Link Arm will open the bowl vent.
Second, we see the screws and small square plastic washers have been installed.
At this point, you need to play with the whole assembly to see how it all moves together. YOu will notice that if you move the mechanisms too far, things will pop out of place and you may need to disassemble some parts to get them back in position.
If you turn the whole assembly over, you should see this:
Be very careful not to damage the parts sticking out of the bottom. You might need to set the thing on a stand so you can work on it without the protruding parts getting in the way:
Step 10 - Attach the bowl cover to the bowl
Now you're ready to attach the two main parts togther: The bowl and the bowl cover. Here you see the necessary parts. Note the awl pointing to two SHORTER screws which are next to two slightly longer screwws. This is important; if you don't use the right screws in the right holes, then things will not bolt together tightly, and gas will leak out around the gasket.
Put a light coat of oil around this piece so it will slide into the hole correctly.
Install this gasket as shown, and be careful that the inner thin part seats correctly It can be a tight fit.
Hold the top piece and position it over the boas shown below. Getting these two parts to mate correctly is one of the most difficult steps because you just have to giggle things and keep re-seating them until the parts line up. It's not easy.
You can place your fingers on the tops of these pins and jiggle them around to help them seat into the holes below.
When things are working right, you can press down on the pump shaft (see below photo) and work the mechanism back and fourth:
This part gave me fits. The bowl vent tab must stay on top on the pump link, as shown below. I had problems with the pump link going up too far at which point the bowl vent tab would slam back down. Then I had to do some disassembly to get things back in order. Once you screw on the cover assembly in a later step, this will prevent the mechanism from moving too far.
Here we see 2 of the 4 screws that hold the bowl cover on. These two are the shorter screws:
The following two photos show where the longer 2 screws go. Note that if you switch the longer and shorter screws, you won't get a tight fit because the longer screws won't seat tight enough, and you'll have a leak at the gasket.
[ to be continued - page under construction]
This page, including text and photos, copyright 2010