Broken Venturi

fundytides

fundytides

Well-known member
My Zenith carb has a triangular piece broken out of the upper portion of the venturi. Does this make any difference? Seems to work ok. Leave it alone or order a new venturi and puller and fix it?
 
I doubt a small missing part of the Venturi would make much of a difference. But if you want to fix it, why don't you tape off the holes in the carb and block off the venturi opening to prevent sanding dust from getting in the carb and apply a little J-B Weld and sand it down to the shape it was?
 
Flow is changed. However, it most likely doesn’t make much of a difference. Personally I would replace the Venturi, they’re cheap and it will ensure it has the correct flow. If it is an original pot metal Venturi I have used a torch in the past to remove broken ones. No need to use a fancy puller on a broken part that won’t be reused in my opinion. They melt quickly and won’t harm the cast. Just be warned the pot metal can pop and splatter a bit when heated.
 
Zenith venturies tend to become stuck in either the top or bottom half of the carburetor. Efforts to remove them may cause damage when it was probably better to leave them stuck in place and move on with the cleaning and restoration of the unit.
 
Thanks guys. I'll get a new Venturi next time I am ordering parts and replace the broken one when I have a chance. Doesn't sound like it's a must do item but might as well have it right. The missing piece is actually fairly large. These carbs seem to function quite well even when they have problems. One time in the 50's, when an A was my daily driver, my car started missing on one cylinder. Investigation found that one valve was not closing. When I removed the head, one of the jets from the carb had come loose and was jammed under the intake valve. Put it back in carb and away we went.
 
This is how the venturi works:
 

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Why is a venturi used and not a simple plate with a hole in it. The hole would increase the velocity too and create a low pressure area to suck in the gasoline.

The answer is that the venturi does not create as much pressure drop and it is thus more efficient.
 
One of the definitions of a Venturi.
A Venturi is a system for speeding the flow of the fluid or air by constricting it in a cone shape tube. In the restriction the fluid must increase its velocity reducing its pressure and producing a partial vacuum. As the fluid leaves the constriction, its pressure increases the flow.
An example of a Venturi would be the large concrete structure typically seen at a nuclear power house used in the process of cooling water. The shape pulls the air from the bottom to the top at a greater speed to the shape of the Venturi.
 
The venturi is more efficient because of its laminar flow characteristics. A plate with a hole would have chaotic flow.
 
Nice thread, just had my carb apart 5 times. Detail, fine point question that could help me. Is the ledge the venturi sits on still the exact point within the venturi? And how do you know the tips are level with the ledge?



Do you have a disc that fits into the space and rests on the ledge and rocks if the jet is high? I looked from the intake end of the carb, but still must estimate as the tip of the jet and the ledge are just out of view.
 
Jeff/Illinois said:
fundytides here is a nicely machined new venturi from Snyder's.

Under 5 bucks American money not sure what that is in Canadian dollars. But cheap.

Don't mess around you probably need a gasket set and maybe a few other items anyway. Good luck.

https://www.snydersantiqueauto.com/...ory=Products/model-a/carburetor/gaskets-parts
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Thanks Jeff. That's the plan. I periodically order several small parts and have them shipped to a mailing depot in Maine and then go pick them up. It's only an hour away and a nice Sunday drive. However because of the current border closure, I haven't been able to do that. The cost of the item is the not the issue, it's the shipping to Canada, plus the "brokerage fee" the carrier ads on to collect the border fees (taxes). I needed a shut off valve a short time ago and the carrier charged $10.00 to collect $7.00 in border fees. By the time you add in exchange on the money and shipping to Canada, actual cost of the item is more than doubled. I'm not really complaining, I'm glad to be able to get the parts I need, but if it's a non urgent item I will wait until I can travel again. Thanks for you interest and stay safe!
 
fundytides said:
Thanks Jeff. That's the plan. I periodically order several small parts and have them shipped to a mailing depot in Maine and then go pick them up. It's only an hour away and a nice Sunday drive. However because of the current border closure, I haven't been able to do that. The cost of the item is the not the issue, it's the shipping to Canada, plus the "brokerage fee" the carrier ads on to collect the border fees (taxes). I needed a shut off valve a short time ago and the carrier charged $10.00 to collect $7.00 in border fees. By the time you add in exchange on the money and shipping to Canada, actual cost of the item is more than doubled. I'm not really complaining, I'm glad to be able to get the parts I need, but if it's a non urgent item I will wait until I can travel again. Thanks for you interest and stay safe!
Click to expand...

Holy crap I forgot about you guys having to pay all of that:eek:
 
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