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.

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.

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

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.

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.

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"

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.

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 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.