Model B Carburator

[rfitzpatrick]

Now I'm Looking for information -- not a Fight.

Mikes Affordable is offering the Model B Carburetor for sale. Is it worth the change-over, other than the price difference? There's a kit needed for installation too.
What's your thoughts?
TKS

[Bob Bidonde]

Use a downdraft carburetor instead.

[alexiskai]

The B carb is the best-performing widely available updraft carb for Model A, but you won’t get the benefits unless your intake is modified to fit the wider bore.

[ModelA29]

You can make the "installation" kit easily. The plumbing section of Home Depot can supply the brass fittings. While boring out the stock intake is best you can grind enough to smooth the transition with it still on the car. You'll get an improvement but not the maximum. If you use a B intake you'll need to file the threads of the mounting bolts where they go through the manifold. This allows you to rotate the carb so the choke rod lines up.

[Synchro909]

If you're looking for better performance but not worried about a non standard appearance, Listen to Mr Bidone (post #2). If you want things to look nearly like original, use a B carburettor. Personally, I recently removed a B carburettor and reinstalled a down draught local Stromberg with its single barrel of 1 1/32 inches. That is within 0.008 inches of the first barrel of a Webber and I find I only use that in normal driving my Webber equipped car.
I found he B carburettor likes a lot more GAV opening and is not as easy to down shift with because it has no accelerator pump. They are less fuel efficient too.

[Dave in Petaluma]

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In contrast to Synchro909, my B carb equipped 68B likes little to no GAV opening, and got 20mpg on a 5,000 mile trip.

[devoreb]

I have a B carb on a 31 Cabriolet. Initially I had the carb without an intake not bored out. It ran very sluggish. I ordered a new bored intake from Snyder's. The car runs very well and I would highly recommend the upgrade. My 2 cents

[rackops]

From my seat-of-the-pants experience (e.g. not technically verified)...in my 1931 Victoria, I drove it with the following:

Model B engine with Model B carb (Model B intake)
Model B engine with Model A carb (Model A intake)
Model A Burtz Block with Model A carb (Model A intake)

Of the carburetors, I built and tested over a dozen from both types (I rebuilt and then sold them on eBay). All of these were Zenith/Holley carburetors, including single and double venturi.

To be honest...there wasn't a huge difference. The Burtz Block engine was different, and I was quite pleased, but as far as how the carburetor affected performance...I didn't see a significant difference. There was never an "OMG! I need to tell everyone that this carburetor is the BEST THING EVER!" event. Once I got both the Model A and Model B carburetors tuned in, they ran well and were dependable. But...nothing incredible happened as far as operational differences.

I will caveat this by saying that I live near the coast and most of the roads here are flat...so I rarely drove up or down hills (save for a local bridge). I am certain hill driving would be different...but I don't have any to test.

I've never driven a Model A with a downdraft, but I have a feeling it would be very different, and quite possibly be the difference in performance people are looking to achieve.

[Big hammer]

My 31 Tudor with 6.0 head , 330 touring cam , counter weighted crank , larger valves, stock intake and stock Zenith carb , Aries muffler, Mitchell’s OD , 3:78 differential gears ,will do about 70 mph flat out level ground or going down hill with a tail wind , is it aerodynamic’s or the smallish intake that keeps the top speed about 70 mph ? How much faster do you want to go ??? Please don’t tell me that you’re a idiot , only did it a couple of times in controlled conditions !

[Bob Bidonde]

I suggest that you use a Model "A" Zenith carburetor with a 6:1 compression cylinder head if you want a stock appearance with more power & better gas mileage. Otherwise, use a Burns intake manifold with a downdraft Holley 94, a 6:1 cylinder head and a stock distributor. Time the engine at TDC with the spark lever down four notches.
The Holly 94 has an accelerator pump, rebuilding kits and a multitude of jet sizes are available. Ford used the 94 from 1937 into the 1950s.

[old31]

A B carb is a much better performer than a Zenith. Snyders sells a bored out intake at a very reasonable price, vs going to a machine shop to get your old intake bored.

[Oldgearz]

Originally Posted by Dave in Petaluma

In contrast to Synchro909, my B carb equipped 68B likes little to no GAV opening, and got 20mpg on a 5,000 mile trip.

No GAV when running for my B carb either.

[Gene F]

Originally Posted by Bob Bidonde

I suggest that you use a Model "A" Zenith carburetor with a 6:1 compression cylinder head if you want a stock appearance with more power & better gas mileage. Otherwise, use a Burns intake manifold with a downdraft Holley 94, a 6:1 cylinder head and a stock distributor. Time the engine at TDC with the spark lever down four notches.
The Holly 94 has an accelerator pump, rebuilding kits and a multitude of jet sizes are available. Ford used the 94 from 1937 into the 1950s.

Down 4 notches.... Bob, won't that beat the babbit out of the rods with a H-C head? Help me understand this.

With the 84, don't you need 12V to run a fuel pump, and regulator? (4's run at like 1 to 1.25 LBS fuel pressure.

[Y-Blockhead]

Originally Posted by Bob Bidonde

Time the engine at TDC with the spark lever down four notches.

Originally Posted by Gene F

Down 4 notches.... Bob, won't that beat the babbit out of the rods with a H-C head? Help me understand this.

With the 84, don't you need 12V to run a fuel pump, and regulator? (4's run at like 1 to 1.25 LBS fuel pressure.

The way I take what Bob suggested is time the engine at TDC with the lever down 4 notches. So 4 notches down on the quadrant is 0° advance.

Not sure what a "84" is but 6v fuel pumps are available.

[alexiskai]

Originally Posted by Y-Blockhead

The way I take what Bob suggested is time the engine at TDC with the lever down 4 notches. So 4 notches down on the quadrant is 0° advance.

Not sure what a "84" is but 6v fuel pumps are available.

He means the Holley 94, and yes, you don’t need to run 12V to run a fuel pump. In fact it’s often helpful, because you can take 12V pumps and run them at half speed, which gets you in the right ballpark pressure-wise.

[ursus]

Originally Posted by alexiskai

He means the Holley 94, and yes, you don’t need to run 12V to run a fuel pump. In fact it’s often helpful, because you can take 12V pumps and run them at half speed, which gets you in the right ballpark pressure-wise.

So, a 12V fuel pump run on a 6V system will run at half-speed? Would pressure at the carburetor be reduced by half as well?

[Gene F]

BTW; I have a car with tripple 94's atop the engine.

I'd think cutting the voltage might be hard on the inline pump. Volts goes down, amps go up. Might be hard on it in a engine compartment.

[Chuck Sea/Tac]

Actually, the B carburetor does have an accelerator pump. It’s called the power valve and it works through closing a vacuum breaker on the throttle shaft, which then sucks up gas and puts it into another port in the body.

[ModelA29]

Originally Posted by ursus

So, a 12V fuel pump run on a 6V system will run at half-speed? Would pressure at the carburetor be reduced by half as well?

Depends on the type pump. You have the old click/clack type pumps that basically energize/deenergize an electromagnet and that pulls a rod to operate a diaphragm pump like a normal mechanical fuel pump that bolts to the engine. The other is a vane pump where an electric motor pumps the fuel - sorta like a water pump. The vane pump may work on 6V but the old style probably won't.

[katy]

Originally Posted by Gene F

I'd think cutting the voltage might be hard on the inline pump. Volts goes down, amps go up. Might be hard on it in a engine compartment.

Methinks you need to read up on electrical theory.