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Discussion Starter #1
I read here some time ago that Edelbrock 750 carbs have a fuel restriction on the secondary side that will only allow them to flow so much. Anybody know anything about this or can point me in the right direction?
 

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Disregard the yellow circle and notes, I sniped the picture off the web. The large tube spun to the small hole in the end and air bleed size is the point of this. The hole in the end of the tube is usually .073" and also they usually have a .073" air bleed orifice in the top of the cluster, centered on the large brass tube below. If the tube is like the one in this pic, hold it between the thumb and finger and wiggle it and pull, it should come out, then put it in a drill motor and spin it and use a file to remove the ball end so the tube is just straight and open. If you have trouble pulling the tube out, use hot tap water to heat the cluster.

 

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Discussion Starter #3
Thanks you for the info. So I pulled the secondary booster out. The bottom of the large tube is .073 and it has three .023 running up one side of it. The air bleed above the large tube is .040. So what do I do with this thing?

Also I measured the passage that runs through the booster and it measures .107. That seems strange to me as I wouldn't think it would flow more than a .107 jet and would also be a restriction.

This is a stick car that I leave with the throttle wide open above 5500 rpm. The air valves have been removed and the choke is taken off. It has also been smoothed with some epoxy to make a gentler and smoother transition into the throttle bores. Also I have -8 inlet fittings, the inner passage that feeds the bowls has been drilled larger, and I have the .110 needle and seats.
 

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do you have to run this carb for a reason.... Class rules??

If not throw that POS in the trash.... If so... continue to polish a turd...LOL

Are you having trouble getting enough fuel in the engine???
 

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Discussion Starter #5
I'm going to keep polishing. :p I run NSS and though the group I run with will allow Holleys, I like the original type look and will give up some power to keep it. It's butting the rings that were set at .034 gap. So its lean or detonating. I richened it up quite a bit and the mph or et didn't improve so thought it didn't want any more fuel. Then I found the rings were butting so now I'm thinking that it's not that the engine didn't want more fuel, It's that the engine wasn't getting any more fuel to begin with.
 

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What are the engine specs??, what fuel you using, plug heat range, timing??

You may have a ring seal issue.
Butting rings with that much gap leads me to believe you have fuel getting past the top ring or aren't completely burning it.
Give us more info.
 

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Drill baby, drill. You are correct, the passages need to be larger than the jet. When you enlarge the nozzle, eliminating that restriction, it may not need as large a main jet.

The use of the emulsion tube is optional. Some OE carbs did not use them, so you might try this without the tube. You can make your own with brass tubing.

In either case, you need to shrink the bleed to .026" or so. Some of the castings are thick enough where the bleed is drilled you can drill and tap 6-32 thread and use brass set screws.

The second bleed in the top of the cluster supplies air to the well outside of the emulsion tube. On initial throttle opening, this pushes the fuel in the well into the tube as an acceleration enrichment, so the volume of the well has an effect.

For what you are doing it is probably best to remove the tube and plug the second bleed (the one outside the tube) and use .026" in the bleed over the center.
 

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Discussion Starter #8
Drill baby, drill. You are correct, the passages need to be larger than the jet. When you enlarge the nozzle, eliminating that restriction, it may not need as large a main jet.

The use of the emulsion tube is optional. Some OE carbs did not use them, so you might try this without the tube. You can make your own with brass tubing.

In either case, you need to shrink the bleed to .026" or so. Some of the castings are thick enough where the bleed is drilled you can drill and tap 6-32 thread and use brass set screws.

The second bleed in the top of the cluster supplies air to the well outside of the emulsion tube. On initial throttle opening, this pushes the fuel in the well into the tube as an acceleration enrichment, so the volume of the well has an effect.

For what you are doing it is probably best to remove the tube and plug the second bleed (the one outside the tube) and use .026" in the bleed over the center.
That's awesome. Thank you so much for the input. I will let you know how it all turns out.
 

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Discussion Starter #9
Drill baby, drill. You are correct, the passages need to be larger than the jet. When you enlarge the nozzle, eliminating that restriction, it may not need as large a main jet.

The use of the emulsion tube is optional. Some OE carbs did not use them, so you might try this without the tube. You can make your own with brass tubing.

In either case, you need to shrink the bleed to .026" or so. Some of the castings are thick enough where the bleed is drilled you can drill and tap 6-32 thread and use brass set screws.

The second bleed in the top of the cluster supplies air to the well outside of the emulsion tube. On initial throttle opening, this pushes the fuel in the well into the tube as an acceleration enrichment, so the volume of the well has an effect.

For what you are doing it is probably best to remove the tube and plug the second bleed (the one outside the tube) and use .026" in the bleed over the center.
What are the engine specs??, what fuel you using, plug heat range, timing??

You may have a ring seal issue.
Butting rings with that much gap leads me to believe you have fuel getting past the top ring or aren't completely burning it.
Give us more info.
I had an issue and didn't know where the grey powdered metal was coming from. Rebuilt it with different pistons gapped at .028. Same issue. The pistons had a lot of rock and that's when I noticed the butting. Different piston design this go around and gapped at .034. The rock is now gone but rings still butting.
409 Chevy stroked to 476. 14:1 comp. iron heads and block. Dual 750 edelbrock on a dual plane intake. 1/16 rings gapless top. 33 degrees timing on c16 fuel. Cranking compression 215. What would I look for to see if fuel is getting past rings?
 

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The Eddy's get a bad rap. I also run N/SS. BB Mopar, has been [email protected] with 2 Quick Fuel 750's. Been [email protected] with 2 Eddy 750's. They're not perfect but also not as bad as everyone seems to think.
Doug
Agree, I have been 9.90's in a 3700lb stock suspension car.
It would be nice to see a thread on modifications that have worked for some on these carbs instead of the "put a Holley on it"

dvw- have you tried a set of 800's yet?
 

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I believe it is “racingfuelsystems”. That is what came up in Tapatalk anyway. Just started looky looing on there and there is a ton of great info on carbs, fuel injection, ignition, and data logging. Glad Mark made the suggestion!!


Sent from my iPhone using Tapatalk
 

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Look at fuelsystemforum.com. It has tech info on many types of carbs and other components.
Thanks,


Yeti, I have opened up the bottom of the emulsion tube on the secondary side, I noticed on a pair of 600's I am building the primary has a small tube as well, should this be opened up?
Thanks in advance!
 

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Discussion Starter #16
I know of two cars that go 8.70s with 800 edelbrocks. I'm out in the garage modifying me boosters right now.
 

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Thanks,


Yeti, I have opened up the bottom of the emulsion tube on the secondary side, I noticed on a pair of 600's I am building the primary has a small tube as well, should this be opened up?
Thanks in advance!
The primary tube has larger holes in it so it isn't as restricted as the secondary, but for what you are doing it is probably a good idea.

You can make tubes using hardware store brass tubing. I recall the primary cluster in 409 carbs had an E-tube with only a single bleed about .028" just below where the tube joins the casting and the tube is open on the bottom. The Mopar carbs and old Carter "Competition Series" carbs (ca. 1970) primary E-tube is open on the bottom and had 3 or 4 .028" bleeds evenly spaced from top to bottom.

On the primary cluster the main air bleed is the brass tube with the pinch at the top sticking up out of the cluster. That should be no larger than .031".
 

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The primary tube has larger holes in it so it isn't as restricted as the secondary, but for what you are doing it is probably a good idea.

You can make tubes using hardware store brass tubing. I recall the primary cluster in 409 carbs had an E-tube with only a single bleed about .028" just below where the tube joins the casting and the tube is open on the bottom. The Mopar carbs and old Carter "Competition Series" carbs (ca. 1970) primary E-tube is open on the bottom and had 3 or 4 .028" bleeds evenly spaced from top to bottom.

On the primary cluster the main air bleed is the brass tube with the pinch at the top sticking up out of the cluster. That should be no larger than .031".
Thanks for the info. Building a set of 600's and a set of 800's to see the difference between those and the current 9000 series 750's I am running now.
 

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Thanks for the info. Building a set of 600's and a set of 800's to see the difference between those and the current 9000 series 750's I am running now.
The 750's need the longer booster that the bottom end of the booster is below the minor diameter of the venturi in the body (which is 5/16" below the 600, closer to the butterfly). The Carter Competition Series carbs were correct, they were essentially copies of the 409 single 4bbl and 375HP 440 carbs and the booster casting is correct. Sometime after Carter folded and the carbs became Federal-Mogul Competition Series (or something like that, but F-M etc.) the production changed to all carbs, F-M and then Edelbrock, 600 (or 625?) and 750 got the same short booster as in the 600's, so the booster is too short for the 750 and metering suffers, the signal wanders instead of correctly following airflow. Idiots.
 

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The 750's need the longer booster that the bottom end of the booster is below the minor diameter of the venturi in the body (which is 5/16" below the 600, closer to the butterfly). The Carter Competition Series carbs were correct, they were essentially copies of the 409 single 4bbl and 375HP 440 carbs and the booster casting is correct. Sometime after Carter folded and the carbs became Federal-Mogul Competition Series (or something like that, but F-M etc.) the production changed to all carbs, F-M and then Edelbrock, 600 (or 625?) and 750 got the same short booster as in the 600's, so the booster is too short for the 750 and metering suffers, the signal wanders instead of correctly following airflow. Idiots.
Thanks, you are a wealth of knowledge on these.
Do you know the reason why the 750 Edelbrock is jetted 113/107 and the 800 is 113/101? Seems lean for a 800. Do this have to due to the booster/venture being bigger on the 800?
 
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