Boring out a carburetor

[Terry, NJ]

I have a couple of "A" carburetors and a "B" carb. (Broken flange) And I was thinking, can you bore the A carb out? You'd need bigger choke and throttle plates and a new venturi, and you still wouldn't have a Diameters of the B, but there would be some gain. After all, we bore I manifolds. Has it been done and what were the results?
Terry

[J Franklin]

What fun we have in the wintertime. Go buy yourself a winfield carb and be happy.

[Dave in MN]

Originally Posted by Terry, NJ

I have a couple of "A" carburetors and a "B" carb. (Broken flange) And I was thinking, can you bore the A carb out? You'd need bigger choke and throttle plates and a new venturi, and you still wouldn't have a Diameters of the B, but there would be some gain. After all, we bore I manifolds. Has it been done and what were the results?
Terry

Brent Terry is or was working on a modification of the "A" carb as you describe. I have not heard anything recently from him regarding his success. I'll PM him and ask him to comment.
Good Day!

[Purdy Swoft]

You also wouldn't have benefit of the high speed jet that the B carb has . You may could enlarge the throat and venturi a bit but not the choke, the housing is too thin . In the best case, the B carb, B cam and bored out manifold only add about three horsepower and no matter what you did to the model A Zenith carb it wouldn't even equal the stock B carb alone . In my opinion a complete waste of time and money. No harm meant, just my thoughts.

[Tom Wesenberg]

I agree with Purdy, but if you're going to try it anyway, then use a broken or welded A carb, so you don't destroy a good carb.

[Charlie Stephens]

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My guess would be no. If there was enough extra material to be bored out enough to do any good Ford would have redesigned the carburetor to save material and cut costs.

Charlie Stephens

[BRENT in 10-uh-C]

While you will never get to the same airflow with the A carburetor as you would with a B carb, Purdy's point makes sense however the high speed jet really was not the problem for me but it was the physical amount of air that can get through the airhorn (choke area). Compare the size difference of the two. If the main jet is resized larger, it will flow enough fuel to compensate however it takes someone willing to continually adjust the GAV for the driving conditions and engine RPM.

I found the the throttle shaft area is big enough but where the rub for me was in the venturi area as it was somewhat restrictive in the way the B shape would set in the A bowl. Funny as this sounds when you say a 'B' carburetor & manifold are only worth 3-4 horsepower ...but that 3-4 is about a 10% increase in Hp!

The biggest reason I wanted to try the project is for something I have termed as a "Stealth" engine. I enjoy showing up on a tour and someone is boasting how their Model-B engine with a finned hi-comp. head and a Weber downdraft carb will run 65 mph. I like having a stock-appearing engine that has a B crank turned into a stroker crank, O/S valves, Stipe cam, modified 6½ Snyder head and a updraft stock-appearing carburetor and tell them "I think my old stock A will do that too".

I am doing this now with a B updraft carburetor and a 3.27 gear. As far as torque loss with the 3.27 in comparison to the B engine, the bigger "arm" in my engine makes up the difference. Thus I just wanted a Model-A carburetor to do it with. My suggestion Terry is, do it for the challenge as it helps you understand the engineering of the Zenith carb.