Is this the fix for Edelbrocks off idle dead spot?

Some of us with 440s have experienced the off idle dead spot with Edelbrock 750s and 800s and it's related to particular engine builds, not a random defect in the carb as I haven't heard of this problem affecting stock 440s. I came across this video and I'm going to try this mod after the weather washes away the salt on the roads.
https://www.youtube.com/watch?v=aX2v-du5ias&list=WL&index=55
Has anyone tried this before?

That mod was the fix for the same problem with the factory AVS. Most drivability techs learned it in the sixties.

It looks like I'm going in the right direction then. Thanks.

^^^ thank you

That is a very good video for someone that insists on running one of those for what ever reason. It would have been better for all those that do not have a full set of tiny drill bits to mention what size the orifice started out at and what size it ended up at. .009" bigger is not the best way he could have communicated his changes.

With all the information and parts out there for the Holley platform carbs, I have always been surprised at the lack of CarterBrock parts and this kind of deeper tuning info given how many are out there.

But one look at the tuning charts for the metering rods and jets should still cause most guys to look for a carb elsewhere. I'll say again, the CarterBrocks are not necessarily bad carbs, it's just that there are much better choices out there today. Heck, in the Engine Masters recent cheap carb shoot-out, the CarterBrock came in last place. Even the Summit carb beat it.

Since the problem seems to exist throughout the AFB, AVS and Edelbrock series, the tube orifice size varies with the booster. We always increased the orifice two drill sizes at a time without paying any attention to the actual drill size.

all they're doing is richening up the idle jet. the idle jet is the small tube in the primary cluster. i do this a bunch and is a major help on factory avs's. in short go to .035" on the 600cfm carbs and somewhere between .037"-.040" on the 750's and 800's. i never use large squirters on anything i drive; they don't work. i do use the tan colored accelerator pumps exclusively. also look for casting flash in the groove that feeds the pump reservoir. simple stuff.

i'm going to add something else. i've found dealing with the 800avs (not the avs2) that taking fuel out does help them drive better off idle. they have a .040" idle jet and don't go bigger. i've reduced main metering jet area and used small squirters to improve tip-in.

74Rallye - is your car out of CA? I looked at one from CA. back around 1984 - looked the same as the car in your avator. It was parked under a car port in Phoenix, AZ. An amazing all original paint car in super condition - 440 automatic. I left a note on it to ask if it was for sale, but never heard from the owner.

Sunroof, My car came from Danville VA and rested in a junkyard in Evington VA before I got it.

That works for you. You must have a full set of tiny drill bits to choose from. But not everybody does.

A post or two later, it is noted that the drill range is " .035" on the 600cfm carbs and somewhere between .037"-.040" on the 750's and 800's." That is more very good info for those that don't want to buy a full set of drill bits to find that one or two that they will need to fix their CarterBrock's problem.

You have a vintage car, and you do not want to buy basic tools? A small index bit set is about $10. You are only drilling alum or brass. If you take your own carb apart to clean and rebuild you would want that set to clean out the bleeds and jets, even if they were sized correct.

Obviously, you misunderstand.

I have worked on CarterBrocks before so I have plenty of drill bits. I was just thinking of the poor guy that buys one of these things and then realizes that he doesn't have enough tools to get it to run right. And there have been plenty of posts on this and many, many other boards from guys discovering just that.

CarterBrocks are not bad carbs, there are just better choices out there today. Ones that don't require a set of drill bits to get to run right.

And I am not cleaning ANYTHING out of my carbs with a drill bit.

The only reason to run an Edelbrock carb on your car is if you need to knock some power out of it to slow it down.

why do these type of carb threads always boil down to carter vs holley vs demon, etc? it's just information; not an infomercial.

Exactly which of the above posts are more infomercial than information? The Engine Masters shoot-out where the CarterBrock came in last? The fact that the CarterBrocks have a well known off idle hesitation that other carbs don't have? The need for a set of special drill bits to fix the CarterBrock's calibration problems?

Wouldn't any open minded shopper want that information before they pulled the trigger on one of these carbs?

What really pisses me off is Edelbrock's head in the sand attitude. All of the time I spent talking to Edelbrock, the many hours spent trying to tune this problem out of Edelbrock carbs, Do you think Edelbrock doesn't know how to deal with this problem? I'd bet they do and they will not share the fix with their own customers. Their final word to me from Edelbrock was that it was the dyno operator's fault. How many times have you seen an engine on the dyno being tuned for off idle performance.?

Been running a 1407 since the eighties. Never had an issue other than a leaky float. Seems to me the issue isn;t a carb design defect but the application needs tuned to.

Seems the people complaining about having to tune a AFB, or whatever Carter you have, forget Holleys need tuning too. At least they do if you want something optimal and that goes for any "universal" type carb out there regardless of who made it.

You want something tuned specifically for your combo, run the factory setup. You deviate from that you will need to address the effects of those changes. You can do it yourself with a cheap set of bits or pay someone else to overcharge you to do the same.

But pissing and moaning about a non issue solves nothing.

Agreed. Only carb in my experience that hasn't needed a bit of tweaking is dead-stock OEM stuff.
The Eddy AVS2 on my '68 RR is a better piece than its 53-year-old AVS, and with a little cosmetic work, now looks very original.
Functionally, all I did was change the metering rods; that system's pretty clever and not hard to figure out.
For some builds, looking stock has a lot of appeal.
The Holley on my racecar has had a lot of work done to optimize it for its application, for that matter...

They're cheap, no excuse for not having the set.

https://www.ebay.com/itm/59Pcs-Prec...l-Bits-Set-Rotary-Tools-Kit/184437419802

I just pulled a spare 1405 (or was it a 1406? ) off the shelf.

A 0.028" drill bit is the biggest that will fit in the orifice. I'm also having an off idle stumble, so I may just drill them out to 0.035"

Had a stumble right off of idle, whether warmed up or not on a new 800 performer eddy carb. Cured it by stretching springs on metering rods about .100" each. That was a 500 inch 400 with a somewhat lumpy hyd cam. Guess I lucked out.

Correction. The problem is not that the CarterBrocks need tuned. It's how difficult they are to tune. And how difficult they are to find parts for and information on how to tune them. The OP talked to the manufacturer straight on and they blamed someone else for their problem. Either they didn't know they had a problem or knew it and hid the info. Which one is worse?

Here it is 2021, this platform carb has been around over half a century and the fix for a common problem that people have been dealing with for decades is still news to many. That is the problem.

35 year old stuff. Probably 15 year old stuff 35 years ago. What's old is new again.

I remember you and I talking about this in the early 1990s. You were giving pointers back then. Probably what you said above.

Even if you don't have the good set of bits, calipers will tell you what'll work.The video said to start at.006". Then increments of .002". Sounds simple enough.

That is a better statement of the problem. Let's remember Carter went out of business. Then the spin offs. Holley won the competition war especially when it came to racing. But I would not classify them as easy to work on either.

Those Edelbrocks are generic AFB and AVS. I have seen them used out of the box and work fine for a basic street car with some minor tuning. Some times I question if they even have engineers testing anymore, or just have the overseas manufacture copy an old design. I do not think many appreciate all the different variations OEM carter had with top size and shape, venturi dimensions, let alone jetting. Same goes for the spin off fuel pumps. Even washer sizes were engineered inside a fuel pump with plenty of patents on the design. All that gets washed away by an overseas manufacture that doesn't know why it was like that but can save some pennies per unit using something more generic.

I would say this for an old carb. You need to take it apart and clean and dimension the idle and fuel jets. Aluminum corrosion, growth, dirt, all tend to shrink the hole sizes. Clean it out really well, and get back to OEM base line. Carter manual or Service Manual give spec for air and fuel bleeds/jet. Have that base line then change for your motor/todays fuel.

As far as my car, this spring we are going to put the Eddy vs Holley power question to rest. Been running a pair of 1407's for 8 years. Won a lot of races with them. Car has been as quick as
1.25 / 5.71@120 / 9.0@150. This year we're going to try a pair of custom built 4150's with lots of tricks. How much better will they be? Will the starting line footbrake performance be quicker? More consistent? Stay tuned.
Doug

And at what RPM are you launching those 1407 s ???

Street Versus Race And Off Idle / Flat Spots Versus RPM are completely eliminated




Edelbrock 1407/1411 where notorious for off idle flat spots / going lean on Big Block Mopars on the street
No damn drill bits where fixing those - Maybe a garbage can or EBay



I like the factory Carter AVS found on the 69 - 71 440 HP motors - So easy to tune when converted over to Eddy internals and flat metering rod covers

With that said , I Absolutely LOVE my Eddy AVS 2 800 - Idle and Off Idle are flawless / perfection to say the least on a street car


Anyways 1407/1411 - From Speedtalk


The secondary venturi cluster emulsion tube is “pinched” at the bottom with a .073” orifice the fuel must pass through to enter the tube to get up to the discharge nozzle….. and (it gets worse) …… the secondary Main Air Bleed is .073”. Imagine what a Holley would do if it had a .073” bleed in the booster leg.

The reason it doesn’t seem to matter what jet size is used is the .073” air bleed kills the venturi signal and no matter what main jet size larger than .073” is used the fuel must pass through the .073” restriction downstream of the main jet.

As if that isn’t bad enough, the primary MAB (the tube pressed in the top of the cluster) is occasionally very large, .040” or more, and occasionally different on left and right.

Occasionally the idle jet (the small tube pressed in the bottom of the cluster) is different left and right and sometimes the idle jet larger than necessary, resulting in a very rich off-idle.

The 1407 750 CFM uses the same casting for the primary cluster as the 625 CFM carbs in spite of the fact the venturi minor diameter is 5/16” or so lower in the 750 body. This places the exit of the booster venturi that much above the “vena contracta” in the air flow, the result is the “booster signal” is not obtained in the correct location and the metering is erratic, the A/F wanders rich and lean as load and RPM vary as the throttle position is changed.

Launch at 2800-3100. And yes I’m chasing inconsistently in the 60ft that is not traction related.
Doug

Interested in your results switching over to the Holleys , especially with what your describing on the Eddy 1407 s if that indeed is the issue

when i got back into the afb/avs i just did some research on old info and service manual specs and applied it. some of the old race tips help too. there's info out there and the edelbrock parts support helps. using some grade school math figuring jet area's instead of just jet or rod numbers helps. i enjoy the challenge and the challenge isn't big. i firmly believe that the afb carb was and still is a very good efficient design.

as for your speed talk quote, and i've read this before, if a careful look is taken at the cluster in question you'll notice an additional flow tube that does help that matter, but if there still is an issue with size the "special" drill bits from a set of number drills solves the problem. there are also clusters out there that have a straight thru emulsion tubes that aren't swaged down. a concern to me with edelbrocks (not the old sand cast carters) is the fuel passages from the jets to the cluster wells. the edelbrocks are smaller and not machined near as nice as the old stuff. holley's do have better and larger fuel passages that could be a make or break deal for someone in competition.

the 1405 that i'm using for a secondary carb on a ch28 did have a .028" idle jet and the 1406 i use for primary had a .033" idle jet. ironically these two carbs were totally different internally in relation to the clusters and jets. i'm using .036" idle jetting now in both carbs but i do have a little bit of cam in the engine and sometimes that needs a little fuel help. i use nothing bigger than .028" squirters with the orange/tan ( 1467 pump) accelerator pump (carbs came with this pump) and no stumble, hesitations, spits, sputters or nothing adverse. power is very smooth and reliable.

I buy Holley air bleed jets the small ones, takes a 6-32 tap, I drill a bigger hole to just sink the jet, then tap it for the screw in air bleed. I think most of these stock have about .040 idle airbleed, I reduce that to around .030 and it fixes idle quality and the stumble. I got the idea on this forum, do a search, the post had photos.
Also on the stumble, fire up the engine let it idle at normal speed, lossen the plate over the metering rod piston, and slide it to the side, be careful so you don't shoot it out, but play with the throttle and watch the piston move, stretch the spring until the instant you touch the throttle the piston starts to rise, makes them very responsive. They do make different weight springs, I seldom need them unless it has a big cam.
The other issue is the AFB carb design, is a very good one, but it is 50 years old at least, we are not burning the same fuel in our cars that they did 50 years ago. Fuel injection systems adjust for a lot of variables, carb adjust for nothing, if you don't want to drill a few holes and change some parts to get it perfect, just buy and injection system and let the computer do it for you. Tuning a carb is a dying art.

from what i can tell the afb's have two idle bleeds, plus an economizer bleed, and several emulsion tube bleeds. they have a bunch of places to mix air with the fuel. i think they are more sophisticated than a holley at mixing air and fuel. i think of a holley as being one step above a lawn mower carb because it has a cruise circut,....lol.


. one race tip is to solder up the air holes in the emulsion tubes.

I have a 1406 (I'm pretty sure ) on my truck right now. Apparently 1405s and 1406s have different venturis, boosters and idle circuits?

It's been several years since I've been in the carb. I'll get the tan accelerator pump (thanks for the part number!), then dig into it at some point.

venturi are the same; clusters are different. circuits are just calibrated different and can be easily changed. 1406's are lean on the primary side. i use .100" jets with 71x47 rods.