Trying out a spreadbore carb on the Duster.

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AlaskaJeff

AlaskaJeff

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So the LD340 intake on my Duster was at some point milled out (quite well I might add) to a spread bore design. I've been running a Holley Double pumper for the last few years but have always wanted to try a spread bore carb to get rid of the adapter/spacer. I recently got a Carter AFB 9635S off evilBay. it's set up with: 100 Primary Jets, .70 x .47 Metering Rods, .095 Secondary Jets, and 5" Step-up Springs. Is it a decent carb? Will I be disappointed with it compared to the Holley?

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The Carter carburetor in your pictures is not a spreadbore.
You should look for a Thermoquad carburetor, Q-jet or a Holley spreadbore. The secondaries are significantly bigger on a spreadbore.
 
Like Mike said, if you want to try a spreadbore, go to a thermoquad. Tuned properly, they are awesome! Second only to the TQ is the square bore Edelbrock AVS2 series. The annular boosters provide vastly improved low and mid range throttle response over any Holley I've ever used. Edit: the AFB you got likely will run better if you also get a calibration kit so you can tune it. Very few carbs are perfect right out of the box, and especially those that are rebuilt. You never know what parts the rebuilders put back into them!
 
Generally speaking, the spreadbore carbs have single holes drilled for mounting them while square bore carbs often have two (so they can be mounted on OE spreadbore manifolds. Holley 4165 carbs (and quadrajets/thermoquads) are a good example of spreadbore carbs.

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All Carter/Edel carbs are great carbs. See below. Carter 625 AFB v 600 Hol. Carter made more tq & hp.....& used less fuel doing it.

Spread bore. The term appeared when the QJ appeared in the mid 60s. To accommodate the huge 2.25" sec t/blades, the c/line of the t/bores had to be 'spread'. Hence the name.

I doubt whether an AFB, AVS or TQ will seal to that manifold without a spacer. There is very little flange metal left on the sides & rear of that intake to seal without an air leak. May fit without a spacer/adapter, would need careful checking.

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AlaskaJeff said:
Am I missing something? It looks like a spreadbore to me

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Technically, it is. Though people will argue. The proper classification for the smaller AFB and AVS carburetors is spread bore, but square flange. Most people only call a carburetor spread bore if the secondaries are the size of beer cans like The TQ and Quadrajet. So, for garage speak, the smaller AFB and AVS carburetors are called square bore.....but they really aren't.
 
Bewy said:
All Carter/Edel carbs are great carbs. See below. Carter 625 AFB v 600 Hol. Carter made more tq & hp.....& used less fuel doing it.

Spread bore. The term appeared when the QJ appeared in the mid 60s. To accommodate the huge 2.25" sec t/blades, the c/line of the t/bores had to be 'spread'. Hence the name.

I doubt whether an AFB, AVS or TQ will seal to that manifold without a spacer. There is very little flange metal left on the sides & rear of that intake to seal without an air leak. May fit without a spacer/adapter, would need careful checking.

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Edelbrock makes like a 1/16" plate that will seal it fine. No need for a thick adapter or spacer.
 
AlaskaJeff said:
Am I missing something? It looks like a spreadbore to me
Click to expand...

What your misunderstanding is that square bore carbs are not always exactly square between the front and rear. Typically, they are like the Holley is. 1.75 on all 4 barrels for example.
The square bore is monkier is still applied when it’s like what you have shown.

The spreadbore is a large difference. TQ, Quadrajet, select Holley carbs are spreadbore.

TQ below.

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