Edelbrock Twin Four barrel Carb info wanted

Richer (sorry for the slang talk)

 

Brewton - we like to use smaller carburetors than many; but use solid linkage. We don't recommend progressive linkage on 2 x 4 setups. At WOT, it doesn't really matter; but for street use, solid linkage, and smaller carbs gives better results at lower RPM's.

Jon.

 

Really, please school me! I always assumed that the reason for the progressive linkage was because a solid linkage would give your motor too much fuel for street use.
How would you suggest setting up jetting for that setup?

 

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.

 

Are there advantages or disadvatages of running two different size carbs like a 500 on one end and a 650 on the other?

 

My Edelbrock 600 on my 350 in the Chevelle always bogs a bit off the line at a stoplight and seems to sputter for a sec in slow speed turns. Car idles 800 rpm fine, (Performer cam) just has that damned bog when you start moving or round a corner. Went to Edelbrock and got the rods, etc reccomended for this altitude. Just under 5000 ft. Results? Absolutely no difference I can see after adjusting the idle. Car cruises at 80 all day long with your foot barely on the gas but mileage ain't great. 12 to 14 MPG on the freeway. Was 10 to 12 before we changed the metering rods, and I have a .273 rear end in this thing. Had the local guy the racers go to tune the carb and still have the same problem. Maybe C9 hit it and it's the springs. This carb also idles just fine here but when I pull into Bakersfield at about sea level I have to stop and adjust the idle as the car will idle at 2500/3000 rpm and chirp the tires when you put the 350 hydro in gear with your foot on the brake and not touching the gas pedal. You're fighting the brake against the torqe converter at the stop sign comming into town. 2 lbs of air pressure makes a BIG difference to this carb.
Some people swear by the Edelbrock carbs, Others swear at them. I'm starting to fall into the latter catagory. I know other guys who swear by the Edelbrock carbs but when you ride with them first thing I notice is they bog a bit off the line too. They've just gotten used to playing with the gas pedal to adapt. Give it a little squirt as you start to move. Once there's a little air going thru the carb it works fine.

 

Joe, you might want to try a 4-holed spacer under that carb.
Get the thickest one you can mount without jamming the airfilter into the hood.

These newer Edelbrock/Carter carbs really could use a better vacume-signal from the motor, and a 4-holed spacer usually does the trick.
It will improve low and mid-rpm power aswell a bit, especially on a single plane intake.

I had a 650 newer style Carter AFB on the Chrysler 383ci with Offenhauser '360' intake. This was in my '65 Chrysler 300-convertible.
The heavy car bogged a little driving off from a standstill. As a test I slid an aluminium 2" four-holed spacer under the carb and the bog was completely gone. The motor really liked the spacer as there was some extra power during take off.
But since I couldn't mount the 3" open airfilter anymore, I had to go back to a 1" spacer.
The engine-bog ever so slightly returned, but I was able to tune it away again.

 

I'll give that a try, thanks

BTW What 2X4 manifold are you planning on. The High Rise is a log so progressive will work, but the short one isn't a log I believe so it would need direct linkage.

 

Fwiw - an Offenhauser on the BB Buick.


I'd call it a medium-rise....

 

Bttt - anyone else have some tuning tips for dual quads?

 

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.

 

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.

 

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.