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#93688 03/22/18 02:13 PM
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I am installing dual Carter B&B carbs on my basically stock 218 six with Offy manifold and cast iron headers. I recently was told this set up will not work, though a lot of guys run it. Its too much carburetion (two much air volume) and will cause poor low end performance. Is this what others have experienced? and is there anything I can do to improve this set up? Thx


RICHARD MARKLEY
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How large are the carburetors?

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The bore is 1 1/2" and the venturi is 1 1/4"


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Yes, that's quite a jump up, and will have idle tip-in and response problems.
What sort of power system do they have?

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Originally Posted By: panic
Yes, that's quite a jump up, and will have idle tip-in and response problems.
What sort of power system do they have?

Ball & Ball carbs have a mechanical accelerator pump that is adjustable based on where a pull rod is attached (controlling the length of travel - pump stroke). This is good for a dual carb setup because it doesn't depend on vacuum.

But to panic's point about a jump: Hollander Interchange shows the original equipment to be a number 11 flange:

Hollander number 11E - which is a Stromberg EXV-2 which has a 1.25" flange. Your 1.5" flange is Hollander number 21 - used on Dodge trucks (21W). Just one is a 44% increase in throttle area:
flange . . . . .radius . . . .r2 . . . . . .area
1.25 . . . . . .0.625 . . . . 0.390625 . . 1.22718463 +44% throttle area
1.5 . . . . . . 0.75 . . . . . 0.5625 . . . . 1.767145868 +0.539961237 sq inch delta

There was also 1 3/8" flange B&B used on Desoto - but that is still 21% increase in just one carb.

When going to a dual one needs to fit carbs that are smaller then the original . . . and/or make engine mods that increase the CFM demands over stock specs.

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Thanks for the quick replies. Looks like these carbs just aren't going to work without some major engine modifications.


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What's the manifold's bolt flange width?
The smaller engines need the #2 (2-11/16”) SAE flange for a bolt-on small carburetor.
The Rochester Model "B" from a Gen-3 (later) 194" L6 looks pretty good, 1-1/2" throttle disc with much smaller 1-1/16" venturi.

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These are D6H2's with larger 2 15/16" bolt pattern.


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There's probably a #2 to #3 adapter, but that will add some height. Re-drilling the manifold will be tough, I would begin by threading 5/16" aluminum rod to 5/16-18NC and bottoming them in the holes with epoxy, saw off flush, then drill & tap the new (closer) holes partially in the rod insert.
I don't see anything small enough to work well without mods, and still fit your flange pattern.
Some Zeniths may fit and have interchangeable venturis, but IDK much about them.

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Considering any other work on the engine?

Of course, what you really need is a 25" Chrysler 265 engine (no, it's not a direct bolt-in).

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Thanks, Panic, for your suggestions and advice. I should have done more mods to the engine when I rebuilt it. The engine is rebuilt to stock specs so probably won't dig into it again anytime soon.
I understand I can do something with small Holley Weber 2bbl carbs from an 80's Ford Fiesta, with adapters, etc. but I don't think it would have the old school look I want. Looking like I will go back to the original single carb and exhaust and move on to another project. Thx to all who replied.


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