Edelbrock carb folks, please read...

[sasilverbullet]

Please read thru this and see if you guys can lend some wisdom please!

A friend's old-school mechanic said that if you are using an Edelbrock carb (mines a 1406) with electric choke (normal choke is ok), there is a manufacture defect/issue where there is a vacuum leak. The guy said use your finger plug the hole indicated by the picture below. (the hole is blue because i took this after I stuffed it with sealant) You'll notice the car suddenly run smoother and you might be able to feel the air with your finger.

That's what the mechanic said...

When I posted this over on the Lincoln forum, I got varied responses, basically they're saying that Edelbrock designed the hole to pass air across the electric chokes heating element to keep it from burning up after it warms up.

Here's some of the posts and links they provided:

it is a controlled vacuum leak
http://www.earlycj5.com/forums/showthre ... tric-choke
http://www.ford-trucks.com/forums/94150 ... choke.html

If one plugs the hole, one should have a way to disconnect the power from the electric choke after the car warms up.

The type of electric choke operation on Edelbrock carburetors goes all the way back to the Carter AFB. Maybe not the most brilliant design concept but at the time it worked (more or less). Strange idle is pretty much of an indication of the choke not being correctly adjusted for the engine and the typical cold engine starting temperature where the car is driven. Plugging the vacuum port as suggested or has been done may well result in a better idle but it is defeating the purpose of the port and probably resulting in a fuel rich operating condition after the engine has reached normal operating temperature. I'm going to suggest if plugging that minor vacuum leak improves engine idle there are other things going on with the engine and analysis to determine what they are should be performed. There are either other vacuum leaks somewhere or timing is off either from incorrect adjustment or a problem with the distributor's vacuum advance motor. There are tens of thousands, maybe hundreds of thousands, carburetors with that exact setup and we all know there are not tens or hundreds of thousands poorly idling engines out there.

Edelbrock (or Carter) may have routed the vacuum leak (or controlled air intake port) through the fuel stream which may not affect the air-fuel mixture. If you don't use the electric choke, you can plug the hole. I would expect the choke coil to burn up if the hole is plugged. That would be bad.

So bottom line is, should I leave it unplugged or plug it?

 

[SteveSRT8]

I would have left it open. Edelbrocks are a lot like Q-jets, very misunderstood carbs.

Quite a lot more knowledge and experience required when dealing with a real carb and distributor.

 

[morris]

get a thin al plate cut it to fit the opening, then drill a .02 to .03 in hole. then mount it all togather. the electric needs to stay on. all so if it is on a spread bore manifold you need the steel plate, to block off a vaccunm cause of the large rear hole for a spread bore set up. all so if you start rejeting, do NOT change the primary jet AND rod at the same time, you can not guess what the change is. change ONLY one at a time. a little is a lot. of the screws holding the lid there is two screws in the middle, one in front and one in the back. you can take them out and leave them out.

 

[Chris142]

I hate those carbs! I never could get them to work right. I had a brand new one that had a lean stumble @ cruise. Shop next door has a dyno room. Spent 8hrs on a dyno and even the experts couldn't make it right.

Plus if they sit 3 or more days they will not start unless you pour gas down the throat.

I broke the baseplate on my Holley and in a hurry put an Edelbrock on the truck.

That one was down 60hp and 90ftlbs vs the Holley that It replaced. I found a used baseplate for the Holley and got my power and Tq back.

 

[morris]

i worked on AFBs for over 30 years they all ways ran great. maybe i was lucky. LOL.

 

[SteveSRT8]

Had many an old Mopar, Lots of AFB's. An excellent carb.

As the above poster found out, the art of tuning is a lot different in the older autos with carbs and distributors. No laptops, no software.

And BTW, I made almost 1000 crank hp with a pair of Edelbrock carbs on an old street car, they can make every bit as much hp as a holley can!

 

[Kruse]

About 30 years ago, I remember there was a 1000 cfm Carter carb that was marketed toward the hot-rodders. Pretty sure it was pretty rare and highly sought after by the pro-Carter boys running big cubes. Sorry I don't remember the model number.
Getting back to the OP, shouldn't that suck filtered air through the exhaust manifold or shouldn't it be heated by the crossover tube underneath he carb to heat the bi-metal choke spring? Is this the setup where it sucks air through the filtered air section of the air cleaner, down to the exhaust to get heated and then back to the choke? If it's for an everyday driver, shouldn't it be left open?

 

[morris]

"1000 cfm Carter carb" was a thremoquad. its trouble was if it got to hot it would warp badly. and there is no fix. saw a guy the had a 1970-71 A body in NHRA stock class, all steel, 340 1000 thermoquad. turned 10.70. ill never say the AFB is a good race........oh wait dont forget the early 60s Max wedges, or the 1966 street hemi ie HP2. wally krueger 1966 b/sa belvedere 10.70

 

[Scott_Tucker]

I've had a lot of problems with the plating on those carbs chipping and clogging passages. A lot of times the problem is straight out of the box. They are great carbs when they are running right but you won't get as much power out of them as a Holley. Isn't the vacuum bleed for the choke pull off?

 

[mechtech2]

You need the bleed.
If plugging it fixes the idle, you are running too lean.
Set the idle mixtures screws properly.
First, make sure your ignition timing is where it should be.
Get her good and warmed up, and pull over and let it idle.
Once you get the 2 mixture screws at the fastest idle, then lean it out 25-50 RPM.
Remember that chokes often require 2 adjustments per year [maybe more!]. The idle too.

 

[morris]

to: scott if you are talking about the new ones , i havent worked on any in a bout 10 years, they must be much different than when i used them. the Edelbrock has a lot of things that need fixed. but if you can get a REAL AFB off a old chrysler it should do good. idle? on the Edelbrock needs the idle jet bored out to .034 in. that will take he flat spot way at off idle.

 

[Scott_Tucker]

Yes, I'm talking about ones made in about the last ten years. At least since Edelbrock took over. The older ones don't have that nickel finish and don't seem to have that problem. I've never had to change idle jets to get rid of a hesitation. Changing jets has always gotten the fuel mixture perfect on ones that are good. We had a flow bench at the Carb shop I worked at so we could usually see the bad ones on the bench.

 

[sasilverbullet]

Originally Posted By: mechtech2
...Once you get the 2 mixture screws at the fastest idle, then lean it out 25-50 RPM...


Will be taking your advice, makes a lot of sense after reading thru all the posts.

Turning in is lean, out is rich, right?

 

[Scott_Tucker]

I personally don't recommend turning the screws in after finding highest idle. It will just make it idle rougher. Adjusting them lean was something you would do for emissions.

 

[SteveSRT8]

yep, in for leaner, out for richer. You can also use a good vac gauge to set them.

 

[mechtech2]

Originally Posted By: Scott_Tucker
Yes, I'm talking about ones made in about the last ten years. At least since Edelbrock took over. The older ones don't have that nickel finish and don't seem to have that problem. I've never had to change idle jets to get rid of a hesitation. Changing jets has always gotten the fuel mixture perfect on ones that are good. We had a flow bench at the Carb shop I worked at so we could usually see the bad ones on the bench.


There are almost always idle screw adjustments on carbs. Idle jets?
The screws ARE the idle jets. [There may be air bleeds but who ever changes them?]
And what would a flow bench tell about future mixture anomalies with different cars, manifolds, temperatures, etc.? [Answer - NOTHING!]

 

[morris]

to scott: on ones i have worked on the idle jet cant be changed. you just have to drill it VERY VERY carefully. starting in 1968 ALL of the AFBs, AVSs had a jean idle jet, that all most all ways have a flat spot, off idle. i have some VERY OLD books that have info that is VERY hard to find. i have one jet chart that is so old, 1968, that some of the numbers are different than later. the two screws in the front are the idle mixture screws, the idle jet, is under the venture cluster, in the small brass tube. if you dont know what you are doing DONT do any thing to it. you will mess it up.

 

[Scott_Tucker]

Originally Posted By: mechtech2
Originally Posted By: Scott_Tucker
Yes, I'm talking about ones made in about the last ten years. At least since Edelbrock took over. The older ones don't have that nickel finish and don't seem to have that problem. I've never had to change idle jets to get rid of a hesitation. Changing jets has always gotten the fuel mixture perfect on ones that are good. We had a flow bench at the Carb shop I worked at so we could usually see the bad ones on the bench.


There are almost always idle screw adjustments on carbs. Idle jets?
The screws ARE the idle jets. [There may be air bleeds but who ever changes them?]
And what would a flow bench tell about future mixture anomalies with different cars, manifolds, temperatures, etc.? [Answer - NOTHING!]


This isn't an air only flow bench. It is a carburetor specific flow bench. It compares air flow with fuel delivery in cc's. For example, you can tell if the mixture is lean off idle if the amount of fuel flowing vs the pressure difference across the throttle plate is out of spec. We collected flow numbers on thousands of different carb part numbers over the last 30 years so we have a very good idea what specific carbs should flow. The point here is, we know what to look for when we take a brand new Edelbrock carb out of the box and put it on the flow bench. We can tell if we need to send it back. You don't tune a carb on a flow bench, but you sure can test them. Its the same as not being able to fine tune an engine on a dyno, you can get close but you'll always get the best results when doing on-road calibration because there are so many factors you can't duplicate on a dyno.

 

[1 FMF]

i would email edelbrock tech and see what they say.
last i remember the few holleys I've had with electric chokes do not have a hole to flow air through the choke mechanism. It's completely sealed, and I haven't had a problem with them over the years. And thinking of the mercarb on my 3L in my boat that has electric choke and no airflow hole, it's also sealed.
so on your carb it sounds like you have a legitimate vacuum leak which should be plugged, but i'm not that familiar with edelbrocks. are you sure it's not a vacuum port for something?

 

[morris]

well i have ever had a flow bench to use. only test drive on the street and drag strip. if i could chose be tween edelbrock or a chrysler O.E.M. carb, ill take the chrysler. i did have a small collection of chrysler O.E.M. carbs, only 25 of them. but lost them when i got a divorce. the other thing i learned was that the person that drives the car/truck should be the best one to tune the engine. but i have found VERY few people that can realy tune an engine. i wouldnt expect edelbrock to know very much. i wish i could adjust the fuel on 2001 dakota V-6 3.9