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Author Topic: Opening up a pair of AFB's, does this make sense?  (Read 510 times)
Shadow71
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« on: March 17, 2019, 08:12:41 AM »

My brother is getting ready to dyno his 68 426 Hemi and figured we should take a look at the dual AFB's and freshen them while we're at it. The hemi is fairly stock, modified intake with center cut out, some port work on heads and mech roller cam, but a fairly mild one. I believe 9.5 Keith Blacks with slightly shaved heads as well.

Anyway, opened up the rear carb (pair of 1968 AFB's) and after everything I've read, was expecting to find .089-.092 jets. Instead I found 3 1.01's and a .083? Also, metering rods are smaller than expected in the .053- .060 range.

Has this carb been messed with, or does this make any sense? I did find one thread where a guy posted Exactly the same combo from a pair of 69 AFB's but no one really addressed the seemingly larger than stock jets. Gotta be more than coincidence that he has the exact same combo with the odd ball .083 jet as well.

Looking for some info as I was originally thinking we might be lean with stock jetting and metering, but now I'm thinking the opposite!

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Shadow71
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« Reply #1 on: March 17, 2019, 10:40:48 AM »

Any chance these were off a Hurst Dart? lol

J7 4432 S (rear)
K7 4430 S (front)

I am starting to find info that says the earlier 66-67 Hemi duel 4's had the jet config exactly like these.

Right rear jet .083 then 1.01's for the other 3.

Man that seems like a big difference from the .077 Right rear, .092 left rear and .089 fronts that this carb is supposed to have.

Was it a common practice to swap to the larger jets from the older platform for more power?
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John_Kunkel
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« Reply #2 on: March 17, 2019, 02:56:40 PM »

Those carbs are correct for a '68 Hemi with an automatic. The intake might have the Vanke mod which requires richer jetting. Mopar offered a kit to modify the carbs for the Vanke mod. Kit P/N was P2836137, not sure what the actual jet/rod sizes were.

https://board.moparts.org/ubbthreads/ubbthreads.php/topics/2626616/vanke-intake-modifications.html
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Shadow71
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« Reply #3 on: March 18, 2019, 10:10:44 AM »

Interesting about the manifold, as the manifold on this Hemi has definitely been worked over. At first we thought is was just so slight butcher work, but looking more closely, there seemed to be some method to the madness.

I opened up the front carb and it would seem that whoever worked on these was trying to duplicate the 66 jetting.

Front carb has the 3 1.01 jets and the .083 in the Primary left side as 66 specs show. (which never made much sense to me?)

Metering rods on front carb are 68 correct 16-341's

Metering rods on rear carb are 16-341 on right side and the correct for 1968 16-543 left. Which makes me think someone screwed that up?

I would always think that Primary jets would be the same and metering rods as well because that is also your idle circuit. Now you could argue that front carb doesn't matter, but looking at 68-70 Hemi carb jets, the primary jets were all matched and on the secondary's were staggered.


* Hemi intake 2 (2).jpg (295.65 KB, 762x1016 - viewed 164 times.)
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John_Kunkel
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« Reply #4 on: March 18, 2019, 10:39:53 AM »

Here's the print for the Vanke mod, compare it to yours...especially the added dam on the floor of the plenum.


* Vanke mod.jpg (165.27 KB, 941x677 - viewed 156 times.)
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Shadow71
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« Reply #5 on: March 19, 2019, 11:39:24 AM »

Going to check measurement this wknd against that schematic, Thanks!

Spoke with a good friend of mine yesterday who happen to have some of the early tech bulletins from Dick L. and others on what the SS 426 cars were running back then.

The 1.01 and .083 jets and configuration in these 68 AFB's are exactly what was in his literature.

So just need to make a final decision on metering rods as the person who jetted the carbs up, left the 68 rods in and I don't think that would work to well for idle and low speed driving.
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