The Ford Barn

PRG999 · 02-03-2019, 08:43 AM

I have 4 model B carburetors I have been taking apart and rebuilding.
They all have different venture sized openings.
They are marked:
1. .866 with a raised number 4 on the opposite side,
2. .866 with a raised number 3 on the opposite side
3. One marked 22,
4. One wide opened Venturi not marked.

I understand the larger openings were for the B Carb for the B engine and the smaller openings were for B Carbs on the A manifold and engine.
Which one would be the best venture for a A engine with a bored out A manifold?

Thanks
Paul

Jim Brierley · 02-03-2019, 11:53 AM

The largest one!

Purdy Swoft · 02-03-2019, 02:18 PM

Amen !!!

Gene F · 02-03-2019, 04:49 PM

How do you bore out an A manifold? I have a B carb, on a B manifold, because the bore is larger (engine has the vales improved, B/F head, etc) I'd be interested in having my March 28 A manifold modified. I have a double venture Zenith, and the B carb seems like a lot of nothing to me. I'd like to try to put my A manifold and Zenith back on. Bet it's not a thimble full of difference if I can get enough air through the manifold.

Purdy Swoft · 02-03-2019, 06:41 PM

I have used an adjustable reamer to enlarge the model A intake manifold . Reaming by hand is a slow process . Most have them bored at a machine shop . If the manifold isn't set up just right the boring bar can run out the side and destroy the manifold . I think that the model B carb with the large venturi gives around 3 horsepower if used with the C head , B cam and model B size intake ports . The larger B carb will give a little help on the top end . Don't expect to get a boost that you can feel in the seat of your pants . The B carb has a high speed jet that cuts in at near full throttle . The B carb is more complicated that the model A Zenith carbs .

Super88 · 02-03-2019, 10:05 PM

Sponsored Links (Register now to hide all advertisements)

Follow this link and select "Intake Manifold Enlargement". It's a PDF file that explains what needs to be done and has photos that shows the procedure step by step. http://www.durableperformance.net/DIY-Help.html

ursus · 02-03-2019, 11:55 PM

Virtually all Zenith-made B-carb venturies are marked for bore. Zenith was a French company so bores for the Model-B were originally marked as 22 (22mm = 0.866 inches, so those marked 866 are the same size). The venturies used in B-carbs intended as replacement units on the Model-A had a 20mm bore.

B-carb sized Zenith venturies were used in a variety of non-automotive industrial carburetor applications and varied in size from 17mm up to 26mm. These odd sizes turn up occasionally.

PRG999 · 02-04-2019, 12:02 PM

Thank you for the replies
PG

02-03-2019, 08:43 AM	#1
PRG999 Member Join Date: Feb 2015 Posts: 61	Model B venturi Question I have 4 model B carburetors I have been taking apart and rebuilding. They all have different venture sized openings. They are marked: 1. .866 with a raised number 4 on the opposite side, 2. .866 with a raised number 3 on the opposite side 3. One marked 22, 4. One wide opened Venturi not marked. I understand the larger openings were for the B Carb for the B engine and the smaller openings were for B Carbs on the A manifold and engine. Which one would be the best venture for a A engine with a bored out A manifold? Thanks Paul

02-03-2019, 11:53 AM	#2
Jim Brierley Senior Member Join Date: Jun 2010 Location: Temecula, CA Posts: 4,085	Re: Model B venturi Question The largest one!

02-03-2019, 02:18 PM	#3
Purdy Swoft Senior Member Join Date: May 2010 Location: Alabama Posts: 8,099	Re: Model B venturi Question Amen !!!

02-03-2019, 04:49 PM	#4
Gene F Senior Member Join Date: Mar 2012 Location: Ohio Posts: 1,958	Re: Model B venturi Question How do you bore out an A manifold? I have a B carb, on a B manifold, because the bore is larger (engine has the vales improved, B/F head, etc) I'd be interested in having my March 28 A manifold modified. I have a double venture Zenith, and the B carb seems like a lot of nothing to me. I'd like to try to put my A manifold and Zenith back on. Bet it's not a thimble full of difference if I can get enough air through the manifold.

02-03-2019, 06:41 PM	#5
Purdy Swoft Senior Member Join Date: May 2010 Location: Alabama Posts: 8,099	Re: Model B venturi Question I have used an adjustable reamer to enlarge the model A intake manifold . Reaming by hand is a slow process . Most have them bored at a machine shop . If the manifold isn't set up just right the boring bar can run out the side and destroy the manifold . I think that the model B carb with the large venturi gives around 3 horsepower if used with the C head , B cam and model B size intake ports . The larger B carb will give a little help on the top end . Don't expect to get a boost that you can feel in the seat of your pants . The B carb has a high speed jet that cuts in at near full throttle . The B carb is more complicated that the model A Zenith carbs .

02-03-2019, 10:05 PM	#6
Super88 Senior Member Join Date: Jun 2010 Location: SE Corner of WI Posts: 169	Re: Model B venturi Question Sponsored Links (Register now to hide all advertisements) Follow this link and select "Intake Manifold Enlargement". It's a PDF file that explains what needs to be done and has photos that shows the procedure step by step. http://www.durableperformance.net/DIY-Help.html

02-03-2019, 11:55 PM	#7
ursus Senior Member Join Date: May 2010 Location: Oregon Posts: 1,374	Re: Model B venturi Question Virtually all Zenith-made B-carb venturies are marked for bore. Zenith was a French company so bores for the Model-B were originally marked as 22 (22mm = 0.866 inches, so those marked 866 are the same size). The venturies used in B-carbs intended as replacement units on the Model-A had a 20mm bore. B-carb sized Zenith venturies were used in a variety of non-automotive industrial carburetor applications and varied in size from 17mm up to 26mm. These odd sizes turn up occasionally.

02-04-2019, 12:02 PM	#8
PRG999 Member Join Date: Feb 2015 Posts: 61	Re: Model B venturi Question Thank you for the replies PG