Secondary Well zenith carb

Klattu1929

Klattu1929

Senior Member
The secondary well opening in lower carb is not threaded, no brass secondary well installed. Looking into the opening there is a step machined partway down the hole. Were some carbs made this way, no secondary well needed?
The carb looks like a zenith but no markings other than an "H" below the intake flange.
 
The early dual venturi carburetors made by both Zenith and Holley did not have a removable brass secondary well and therefore no threads were in the lower half. The main and cap jets are usually in a straight line from front to back and there might be pin boss/s that were used to retain the dual venturi.
Dave
 
Now it makes sense, I wondered about the pin retaining the venturi. It had been updated to the later venturi at some point. I'll keep on keeping on with the rebuild, thanx a bunch.
 
Klattu1929 said:
Now it makes sense, I wondered about the pin retaining the venturi. It had been updated to the later venturi at some point. I'll keep on keeping on with the rebuild, thanx a bunch.
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Double venturi
 

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If you look carefully at the position and angle of the 2 main jets in the lower carb body half, you can see the difference between the early dual-venturi carb and the later single-venturi carb. There are probably photos of the two online for you to compare.
 
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When converted to a single style venturi and no brass secondary well, how well does this carb work? Is it comparable to the later model zenith carbs. I was going to put it on a stock motor in a '29 35A phaeton. Don't wanta go down this road if it's a dead end. Need some expertise here, Thanx.
 
Klattu1929 said:
When converted to a single style venturi and no brass secondary well, how well does this carb work? Is it comparable to the later model zenith carbs. I was going to put it on a stock motor in a '29 35A phaeton. Don't wanta go down this road if it's a dead end. Need some expertise here, Thanx.
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No. This is addressed in the Ford Service Bulletins (pg. 443). The double venturi carb bottom half really needs to use a double venturi.

If you mix the parts up as you propose, you will have a throttle response lag when you accelerate. (I don't remember if the Service Bulletins go into this in detail. It's a carb design thing.)
 
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