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Old 11-24-2019, 11:21 AM   #1
Gary WA
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Default Double Venturi Carb using?

Anyone using a Double Venturi Carb? Do you see any differences from a standard Zenith?
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Old 11-24-2019, 11:52 AM   #2
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Default Re: Double Venturi Carb using?

Does anyone have a diagram of a double Venturi carb? I'm having trouble getting my head around it.
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Old 11-24-2019, 12:06 PM   #3
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Default Re: Double Venturi Carb using?

Quote:
Originally Posted by History View Post
Does anyone have a diagram of a double Venturi carb? I'm having trouble getting my head around it.

Upper and lower castings are different from later, also secondary well has NO brass well insert.


Idle jet is longer.



Cap and main jet are inline i.e. not staggered.



Photo of venturi here.

https://modelastore.com/index.php?ro...roduct_id=3992

Last edited by Benson; 11-24-2019 at 12:11 PM.
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Old 11-24-2019, 01:49 PM   #4
Gary Karr
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Default Re: Double Venturi Carb using?

I have the first generation Zenith double venturi on my ve-28. It runs really smoothly and almost seems to start faster than my Zenith 2 Holleys.
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Old 11-24-2019, 02:04 PM   #5
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Default Re: Double Venturi Carb using?

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Originally Posted by Gary Karr View Post
I have the first generation Zenith double venturi on my ve-28. It runs really smoothly and almost seems to start faster than my Zenith 2 Holleys.
Thanks have a couple rebuilt but haven't tried yet
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Old 11-26-2019, 12:33 PM   #6
Bob Bidonde
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Default Re: Double Venturi Carb using?

The Ford Service Bulletins, Pages 206, 207, 208 & 209 give an excellent description and operation of the Zenith Double Venturi carburetor.


The Secondary Venturi (#10) increases the inlet air velocity at the tips of the Cap and Main Jets. Notice in Figure 420 on Page 206 how high the throat of the Primary Venturi is above the tips of the Cap and Main Jets. The Double Venturi was thought to provide better acceleration.

In September of 1928 another service bulletin was issued describing the change to the Single Venturi Zenith Carburetor (Page 280). Note in Figure 569 on Page 280 that the throat of the new venturi is lowered to about the same position as the double venturi throat. The changes in flow necessitated changing the Main Jet and the Cap Jet orifices.

As for performance, removing the Secondary Venturi from the inlet air passage improves the inlet air flow volume and smooths the flow stream which produces more high speed power than the Double Venturi.

The Venturi in either the Double or Single design has no effect on the idle circuit. In the Single Venturi Zenith, the new Idle Jet, the new Idle Jet Well, the Compensator Jet and the new throttle plate affect idle performance.
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Old 11-27-2019, 09:29 AM   #7
al's28/33
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Default Re: Double Venturi Carb using?

My double venturi has not let me down in 18 years of ownership. The only fuel issue I had was when I first got the car and had a secondary modern filter on the gas line. It was always in need of cleaning and would starve the carb of gas when I was in the middle of traffic. Removed it and no issues ever since. Keep your cars the way they came off the assembly line.
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Old 11-27-2019, 02:33 PM   #8
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Default Re: Double Venturi Carb using?

Quote:
Originally Posted by Gary WA View Post
Thanks have a couple rebuilt but haven't tried yet

Just a couple
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Old 11-29-2019, 09:05 AM   #9
JD 1931
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Default Re: Double Venturi Carb using?

I have a early double venturi that I rebuilt and run, it is very nice with all the original parts except a new double venturi and shows no signs of wear or pitting.It preforms well but does not have the top speed as the single. I like the sound of it at idle, can hear the air passing into it....
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