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Old 09-02-2009, 08:58 AM   #41
ajmopar
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Default Re: Edelbrock Twin Four barrel Carb info wanted

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Originally Posted by carbking View Post
Most of the "luxury cars" using 2 x 4's used solid linkage.

Most of the "performance cars" using 2 x 4 setups came with carburetors which were actually too large, and progressive linkage.

The car manufacturers were not dumb. They knew if a car would be raced, NHRA was not going to allow a larger carburetor(s) for use in stock class; so the car manufacturer would deliberately use larger carbs (for racing) than would be required for street use. Since the carbs were too large; they (the manufactures) came up with the primary/secondary thing for street use, thus progressive linkage.

Our testing indicates much more even cylinder temperatures at lower RPM using smaller carbs (like the luxury cars) and solid linkage. Street drivability is improved. Again, at WOT, solid or progressive doesn't matter; as everything is wide open.

However, please don't get the idea from this post to use solid linkage if you have too large a set of carburetors for the application.

Jon.
So, what about the 2 AFB's on a 426 Street Hemi? Progressive linkage and I do not think they were over carbed!

I have experience with a progressive setup vs solid and the only difference I noticed was fuel mileage going down with the solid linkage and the "Pedal feel" being a bit better because you were opening more throttle with the same movement of the pedal.
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Old 09-02-2009, 09:02 AM   #42
C9
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Default Re: Edelbrock Twin Four barrel Carb info wanted

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Originally Posted by Brewton View Post
Bttt - anyone else have some tuning tips for dual quads?

Other than just getting in there and giving things a try?

Kidding aside, Carter/Edelbrocks are easy to work on and changes don't take much time.


On your car, I'd be inclined to set up the carbs in factory-issued condition.

Check float level and drop.

You may want to get a few gaskets for the float bowl cover.
They're reusable if somewhat fresh, but if they tear, use new ones.

Start with springs and see how it goes.
You may not have to go any farther.
Right now, that's the only change that was made to my dual 500 setup - which was for 350' altitude.
That'll probably be changed once the 31 roadster is up and running.
Living at 3400' altitude now.


Keep in mind that a pair of carbs at wide open throttle are only flowing about half the air that a single carb does at wide open throttle.
That's why stock jets/rods work and if changes are required, they'll just be small ones.


Rather than buy the expensive Strip Kit that has a lot of parts that don't get used, figure out where you want to go and buy the rods and jets individually from Summitt or the like.
A set for either side of what may be optimum is a good idea.
Summitt delivers fast, overnight on small stuff to my house from their Reno warehouse.

Keep an eye out for older Strip Kits at the swaps.
The last one I bought was complete, cost $5.


Double check metering rods for straight.
Remove the piston, let the short leg hang over the plate and roll it back and forth.
They can be straightend by judicious use of a pair of needle nose pliers.
Use care here.

A dial caliper that reads in thousandths is a big help in identifying the rods.
They have a part number stamped on them, but you may need a magnifying glass - and your glasses - to read them.

Use a vacuum gauge to help set up the idle mixture etc.


The Edelbrock site has a manual.
You can't hardly go wrong getting the tuning info off that.

(I'd list the address, but Adobe's PDF doesn't work every time on my computer - which is new.)


And . . . before I started tuning the carbs, I'd make sure the timing is spot-on and the advance mechanisms are working as they should.
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Old 09-02-2009, 10:27 AM   #43
carbking
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Default Re: Edelbrock Twin Four barrel Carb info wanted

ajmopar - The street hemi used a pair of Carter 625's AFB's which were plenty WITH THE TECHNOLOGY OF THE DAY EVEN FOR RACING!

The proof of the previous statement can be found in the "optional" "drag-strip pack" which was a pair of 750 Carter AFB's. While we have never owned a set of these, we have made and sold several kits for them. Every single customer swears that the 2 750's were SLOWER than the 2 625's. Additional proof may be found in that Carter made only a single run of the 750's while continuing to build 625's for the hemi.

We find mileage on solid linkage will actually improve; but just barely. A good estimate is 3~4 percent improvement. Measurable, but not going to be appreciably noticeable. We do find more crisp throttle response, and as stated earlier, more even cylinder temperatures with the solid linkage. BUT, the progressive will work. If you like progressive, use it.

Jon.
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