Zenith secondary well

marc silva

marc silva

Senior Member
How far do you screw in the secondary well on a Zenith carb.? So it is flush with the casting? The threads on the carb I am working on will allow it to thread in deeper. Thanks, Marc
 
Marc,

Most carbs that I have dealt with have secondary well screwed in tight so that brass is below the deck and about even with beginning of threaded part inside.

As long as you can put the upper and lower castings together with idle jet installed, along with one bowl gasket you will be fine.


Note idle jets do not have a gasket ... The tapered seat seals the jet...
 
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The Cap Jet gets gasoline that passes around and under the Idle Jet Well.


So the deeper the Idle Jet Well goes into the casting, the smaller becomes the gasoline passage to the Cap Jet.


The Cap Jet needs an unrestricted supply of gasoline to provide good acceleration in low to high speed running.



Thus I suggest that you install the Idle Jet Well so it is flush with the top of the lower body to maximize the gasoline passage to the Cap Jet.
 
I just installed a secondary well as suggested in post 4 ... almost level with top of casting!

Guess what? ... just like I thought ...

The idle jet bottoms out in secondary well more that .250 BEFORE the upper and lower castings seat on each other!

In order to install bolt in carb the idle jet will have to be cut about .300 shorter.

How well is the carb going to work?


Bob Bidonde said:
The Cap Jet gets gasoline that passes around and under the Idle Jet Well.


So the deeper the Idle Jet Well goes into the casting, the smaller becomes the gasoline passage to the Cap Jet.


The Cap Jet needs an unrestricted supply of gasoline to provide good acceleration in low to high speed running.



Thus I suggest that you install the Idle Jet Well so it is flush with the top of the lower body to maximize the gasoline passage to the Cap Jet.
Click to expand...
 
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There are several variations of the well with a unique profile. The groove in the correct well provides a channel for fuel.
 
There are 3 types of original secondary removable wells; type 3 is the one to use, it is the one that is being reperduced , it has a recessed grove under the compensation jet so the gas is not obstrucked entering the secondary well. Original compensation jets are very short and use a gasket that keeps it from going in to far, some of the replacements are to long and are junk.


Ron
 
My old secondary well was screwed in/down as far as it would go. I screwed my new secondary well in/down as far as it would go just to get the jet to clear and the body pieces to come together. Carburetor runs just fine, has plenty of idle fuel and power.
 
The well is supposed to be screwed in tight.Where did the idea come from that it could only be screwed a certain amount?Am I missing something here?If it is just screwed in and left loose the threads are going to consume themselves.
 
I agree, the secondary well should be run all the way to the bottom and tightened. I usually shine a light in through the hole for the comp jet to see if it is lined up with a recess in the secondary well.


The only times I have ever seen two gaskets on a comp jet was when someone mistakenly installed a GAV valve seat used on the early Zeniths; they are slightly longer.


Tom Endy
 
I was wondering who and how someone came up the idea to not screw the well in all the way. Wrong information.
 
I have built hundreds of model A Zenith carbs and always have screwed the secondary well all the way until tight....JD
 
Tom Endy said:
I agree, the secondary well should be run all the way to the bottom and tightened. I usually shine a light in through the hole for the comp jet to see if it is lined up with a recess in the secondary well.




Tom Endy
Click to expand...

I think that is what Bob was trying to get to, if the secondary is at the wrong level it can block the compensation jet from supplying fuel.
 
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