Here is a tutorial on rebuilding an AFB Carburetor. First off there are lots of little levers and springs on a AFB so take lots of pictures before you start if you don’t take these apart every day. This particular carburetor is quite rare being from a stock Studebaker 289ci R1 engine. I purchased this carburator a few years ago and has been sitting in a box in my shop since it arrived. I was pushed into rebuilding this carburetor since our Lark would not start with the stock 289ci 3726SA AFB that I had on the Lark a few years ago. These two carburetors are different although they look the same. I believe the CFM’s and jetting are different between the two. Our engine will flow really good with the the heads that I have put on the engine, so the optimum choice for rebuilding is the actual R1 carburetor.
Here is the used carburetor right out of the box from an Ebay seller. It was hard to believe the amount of flaking residue inside this Carburetor. I knew it was going to be bad when I took the air line and blew it out. Wow what a cloud!
I’ve rebuilt a couple of these carburetors over the years but it’s best to take lots of pictures of the levers and spring.
I took the carburetor apart on the kitchen table after supper, gathered all the parts together and took them out to the shop to soak in carburetor cleaner over night. It was hard to believe the amount of crud in this carburetor. The fuel bowls were encrusted with what appears to calcification. You can see the same “calcifaction” on the outside of the carburetor, it’s a hundred times worse in the fuel bowl.
I bought this carburetor cleaner a few years ago and have cleaned a few AFB’s with it. It really stinks and the smell clings to your clothes.
You can see the “calcification” within the fuel bowls. Also had trouble removing one of the secondary jets and the check valve that meters the accelerator pump. I had to drill the primary jet out and remove it with a extraction tool. I managed to use a small chisel to finally remove the check valve.
One last bath after I used my Dremel to buff out the last of the calcification within the carburetor.
I really like this little Dremel tool I recieved from my son for Christmas. I used it to buff out all the little levers and rods. All the little parts are ready to be re-installed.
After much polishing with a Dremel, probing a small screw driver to remove any remaining debris, more washing and blowing compressed air, the carburetor base is looking really good. I also took some fine emery cloth to polish out the accelerator pump to make a smooth surface.
Secondary Venturi installed with the small gasket
Primary Venturi’s installed with small gaskets between carburetor body and venturi. Installing pump discharge jet needle under the pump jet housing and gasket.
My collection of metering jets from a strip kit. I am going with .089 jets in the primaries and .077 in the secondaries. I don’t think this is the ideal jetting but it will be good enough until I tune this carburetor in the spring time with a Innovate Air/Fuel meter. I suspect I will be using Richard Poe’s combination of .089 in the primaries and .083 in the secondaries with a 6842 metering rod and silver spring
The base of the 3506S R1 Carburetor is complete with metering jets installed in primaries and secondaries.
Time to move on to the carburetor top. Here I am installing the seat and gasket for the needle. The carburetor tops gasket needs to be installed first.
Both needle, seat and floats are installed. This picture also shows the accelerator pump installed. This is where rebuilding the carburetor get tricky. Setting the floats. Float must be parallel to the edge of the carb top. I will be using a 7/16 drill bit to set the float height by bending the float- then you have to set the float drop with the top inverted. 15/16″ is ideal for float drop. Caution when you bend the float for height that you do not press the needle into the seat to cause damage to the needle.
Adjusting both floats with a 7/16″ drill bit.
Now adjust the float drop to 15/16″ by bending the small tab at the back of the float.
The finished 3506S R1 Carburetor. I installed the original metering spring and 16-99 metering rod.
This is the 16-99 metering rod and a package of blue springs (not used in this application). Springs are available in several strenghts and are colour coded – available in Blue, Yellow, Orange, Silver and one other colour. Depending upon the vacuum your engine produces different colours are used to tune the carburetor.
The finished 3506S R1 Carburetor. I installed the original metering spring and 16-99 metering rod under the two little plates off the centre of the carburetor.
FInished sideview of 3506S carburetor
Finished front view of 3506S Carburetor
The carburetor looks fantastic, quite a difference a day makes. Now to install it on the Lark’s new engine and start the Studebaker up for the first time.
It’s been a few months since I did the rebuild on this carburetor and got the engine running on the Lark. The carburetor performs perfectly. I am still amazed how well the carburetor looks after buffing out all the parts… it really looks and performs like a new one.