Dual 4 bbl question


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By Kahuna - 17 Years Ago
I am going to run dual 4 bbls on my v8. I am going to use 2 Holley series 4000 carbs (like used on T-Birds). I was made aware of there being some sort of balance tube that needs to be run between the two carbs to balance the secondary openings. Can anyone describe this to me or perhaps show a picture of this application? Or, direct me to somewhere that I might see something like this?

The application is a large displacement Ford Flathead V8. Both carbs will be directly linked (not progressive), with one carb facing it's normal direction, and the other reversed. 

Thanks for any and all assistance.

Jim 

By PF Arcand - 17 Years Ago
Jim: the dual carb setups weren't just any 4000s as I understand it. They were a matched set. As I recall the List numbers were 1434 & 1437, but I can't find my records on that, so could be wrong on it. Also do you have someone who is competant to redo the carbs? They are a bear to do according to some people. I've never tried to do one, so it's just what I've heard.
By Kahuna - 17 Years Ago
Hi Pete

Thanks for the response. I've rebuilt them with good success, and am running one now on another engine. As far as having a matched set, I don't, but really don't think it is necessary for my application. I'm just trying to figure out the balance thing.

Regards

Jim

By Kahuna - 17 Years Ago
Hi Paul

Sorry for the wrong name posting. My mind is slipping.. Old age showing. Again, My apologies.

By Hoosier Hurricane - 17 Years Ago
Kahuna:

On the right rear of the carb, just below the air cleaner flange, is a horizontal boss in the casting with a drive-in aluminum plug, about 1/4" plug with about a 5/16" head.  It is where a vacuum passage was drilled to supply a signal to the secondary diaphragm.  On the factory dual quad carbs, instead of the plugs short tubes were pressed in, and a 1/4" vacuum hose connected the two carbs.  I would wonder if your flathead is big enough or winds high enough to even open the secondaries on two carbs however.

John

By Ted - 17 Years Ago
Here’s a picture of the factory dual quad with the tubes and ¼” hose to which Hoosier refers.  Drilling and tapping both of the secondary diaphram covers for hose fittings and connecting each with a hose will also accomplish the same thing if you’re after a shortcut.  The secondary springs in the dual quad carbs were also of a reduced tension to compensate for the weaker vacuum signal that occurs when going with multiple carburetion.  Also keep in mind that the factory dual quad carbs had downsized flow in the primary sides of the carbs by lieu of larger diameter primary fuel discharge nozzles to help initial throttle response.
By Kahuna - 17 Years Ago
John & Ted

Thank you both so much for the information and picture. I really appreciate the help, and it will make things much easier for me. Great site.

John- the engine is 288 cubic inches, will rev beyond 6k. My thinking is that since the carbs are both vaccuum secondary types, that they will give the engine only what's needed. Thus the balancing questions.

Again, thank you for the info and Best regards.

Jim

PS- How rare and difficult are those air cleaners to find?

By Ted - 17 Years Ago
Kahuna (1/9/2008)
How rare and difficult are those air cleaners to find?

Reasonably difficult as the teapots require a taller than normal air cleaner.  The original factory air cleaners are hard to find even when considering the number of them that were produced in 1957.  But I see where the large round version is being reproduced for the restoration guys.