Carb Adjustment Question

[Jason Bourne]

Overall the truck is running fine. It does have a issue when the truck is fully warmed up it acts like it is going to die at stop lights. It idles fine in Park and Neutral.

The truck has a Edlebrock 1406 carb installed. I'm thinking it might need an adjustment for this issue. I don't know much about carburetors. Does this sound like a carb issue? If so how and what do I adjust? I am attaching pictures of my carb. Maybe it's something Else?

Thanks for any help.

[geezer#99]

That black sooty area in front by the mix screws tells you it’s flooding a bit.
You likely need to lower the float level or reduce the fuel pressure.

[54blackhornet]

Soot inside primary also, to rich mixture. Hopefully you can just readjust the two mixture screws up front. Google, or go to the carburetor manufacturer site.

[Steeveedee]

I'd also suggest spritzing carb cleaner at the driver's and passenger's side of the primary throttle shaft to see if the idle speed changes. Both Edelbrock carbs I've had have leaked from wear over time and had to have bronze (brass?) bushings installed. To be fair, I had to do the same with the Q-Jet on my truck. Difference is, the Edelbrock has a lot of other issues that the Q-Jet doesn't have. Search it!

[Sheepdip]

Pull your distributor cap and pull the vacuum line to your carb suck on it to see if the advance plate moves. Wanting to die at a stop sign is a sign of advance not working properly. Rusted plate or bad diaphragm will cease any movement. Also make sure that particular hose is connected to manifold vacuum below your bottom butterflies.

[CC69Rat]

Are you running a factory style fuel pump? The typical mechanical fuel pump is going to push around 9psi.

The 1406/1407 carbs like around 4.5-5psi. Edelbrock sells a fuel pump specifically for this series carb. Or of course you could add an inline fuel pressure regulator. My .02. I think your fuel pressure is too high and it's causing the fuel to flood the needle and seat. It's a pretty common issue on the AVS series carbs. There are several articles online about it.

I'd put a good quality fuel pressure regulator on it. Start at 4.5psi and drive it. Adjust from there.

This could also be a heat issue in the carb. It runs fine and as you drive it, it gets worse, stalls at stoplights, Hard to start it if it's hot. Let it cool off and it will start back up. Edelbrock offers a phenolic spacer commonly used with these carbs to help minimize the heat issue. The heat from the intake soaks into the aluminum body on the carb and causes the fuel to boil. The spacer kinda insulates the carb and holds the heat down


Add the spacer, fuel pressure regulator and it will be a different truck.
Hope this helps


Article on the fuel pressure issues
https://www.carburetor-blog.com/know...oubleshooting/

[Rust_never_sleeps]

Is the choke flap opening all the way?

[Jason Bourne]

Thanks for all the suggestions! I’m pretty much a total newbie when it comes to carburetors. I did find some videos online about adjusting the carb. Basically they talked about hooking up a vacuum gage to the carb and adjusting it for maximum vacuum. It didn’t look to bad. I’m just paranoid about getting it too much out of whack and then not being able to get it back to at least where I was.

I had to do some googling about carbs to find out some of the things suggested.

I think the 1st thing is to try adjusting the carb. I also think adding a pressure regulator is a good idea and easy upgrade. As far as I know it’s a standard fuel pump installed.

I will check out the choke plate and other ideas.

It could be something with the distributor as suggested but I’m a little nervous about opening that up.

This is my sons 1972 C10 but we enjoy working on it together. We just got through changing out the inner grill, front bumper, and oil change. Next on his list is to install a new chrome rear bumper. It also needs new plugs and wires. New plugs and wires alone might make a difference.

[54blackhornet]

I wish my father had done what you are doing with your son…

['68OrangeSunshine]

You need to clean your carb, then adjust it. Edelbrock kit 1477 covers the AFB type.
Ask Edelbrock for a Performer Carb Owner's Manual. They're free.
The smudge at the back of the carb suggests a manifold leak -- which would manifest as your stall symptoms. Once rebuilt, with a fresh gasket, you should get a good seal.

I have a Edelbrock 1404 [500 CFM] on my 292 L6 in the '68 C/10, and a Carter AFB 9635S [600 CFM] on the 350 in my '71 GMC Jimmy.
[When Federal Mogul stopped selling Carter carburetors ~2000, Edelbrock still made them as ''Performers''. Same carb, built in the same Weber plant, just different marketing.] The AFB 9635 approximately equals an EDL-1405.

[72SB]

Have a 1406 and have used them on a few SBC & Ford motors. They basically are a Carter AFB.

You can download the 1406 "owners manual" which comes with the carb. Very detailed on adjustments

OP, put your vacuum advance on the other port (DS) on front of carb. That is manifold vacuum. You currently have it hooked up to timed, aka ported, vacuum, never do that.

You need to confirm your timing is good before making carb adjustments. You want 20-24 degrees advance WITH VA connected at idle. Generally 10-12 degrees base WITHOUT VACUUM ADVANCE, then with VA connected it should add another 10-12 degrees for a total of 20-24 degrees at idle. Without VA connected at 3k RPM you should have 35 degrees of timing.

Set idle after motor is completely warmed up and confirm choke if fully open. "Maybe" your idle was set before choke fully opens and when it does, its to low.

Appears you have been running rich so get the carb cleaned up with some carb cleaner. A Vacuum gauge is very helpful in tuning a carb. Vacuum leaks will mess up everything so fix those if you have them.

Generally the mixture screws on front of carb are set about 1 1/2 turns open. Both need to be same. In fine tuning you may need to open or close them about 1/8-1/4 turn to get it right. Then set idle RPM. 650 if manual, 750 if auto (in neutral). Cam motors typically need a little more RPM at idle. Sometimes 825-850 ROM.

Edelbrock makes a tune kit specific to 1406 but really not needed for stock motors. Camed motors making power than you need that kit.

[54blackhornet]

I have a AFB sitting on the shelf because no one seems interested in them anymore ? Took it off a 350 that I parted out. Was going to install it on my little 307 but I finally got the TwoJet to work properly.

[tim_mc]

I echo all that have mentioned a fuel regulator. Edelbrocks like 4-6psi of fuel pressure. I had a 1405, now an AVS2. With no regulator, it will run too rich and load up at idle.

Also, when fully warmed up, that's when stuff expands, so it could be a vacuum leak or fuel boiling when warm. I use the Edelbrock 9266 carb insulator to isolate the carb since aluminum conducts heat (too) well.

Likely not related, but my truck was stalling at stops and loading up. I was CONVINCED it was a carb issue. Turns out I had a weak spark from my Delco HEI. I changed the coil and module to Davis Unified Ignition (DUI) and WOW. Exhaust burns clean, great idle and no issues since. Thread for those interested:

https://67-72chevytrucks.com/vboard/...d.php?t=822473

[PanhandleShantyman]

I'd just add that if you're worried about your fuel pump pressure being too high, it's easy to check using the vacuum gauge you already have (they mostly have a positive pressure reading ability too, and come with connectors for fuel line) just disconnect the fuel line at the carburetor, hook it to the gauge, and crank the truck and read the pressure quick before your float tank runs out of gas.

Also maybe one clarification question, is your truck trying to die *at idle* at the lights, or when you hit the gas to get her rolling?

[Dashman]

It's called "Vacuum Advance" meaning that the "timed port" vacuum advances the timing for better fuel economy at cruising speeds. "Manifold vacuum" would advance the timing at idle. Really? What's the point of disconnecting the vacuum hose to set the timing to say 12 degrees, if your then going to plug it into "manifold vacuum" and advance it to what, 20 degrees? You all know that manifold vacuum dissipates with more RPM, right? So you're setting timing to say 12 degrees with vacuum hose disconnected, to say you did, then letting the vacuum canister advance to whatever it wants to with manifold vacuum at idle? Then your distributor is retarding due to dissipating vacuum at the same time that it is advancing due to centrifugal advance. <insert SMH emoji here> Sorry OP, not directed at you because you have it right.

I would check that your float adjustment isn't too high. Your engine could be running slightly rich with higher RPM, but too rich at idle when warm.

With that same carburetor, I experienced fuel boiling at temperature and at idle. My engine was bored over 0.030" with 10:1 compression ratio, so it was going to be hotter that a stock engine. I had a large 3 core aluminum radiator that would keep it very cool, until speeds were less than 25 mph or stopped. That's when the fuel would start to boil. I also had a manual control electric fan to cool the engine, but the cure for the carburetor was a phenolic carb spacer. Keep in mind that the Quadrajets all had thick carb gaskets. I also changed the jets and rods to match my altitude of 6,000 feet.

[Jason Bourne]

This is all good information. Thanks to everyone that has posted. Things have heated up at my sons work, so it may be a little while until we get more time to work on his truck. I will update this post once we have had a chance to try some things out.

[Jason Bourne]

Originally Posted by PanhandleShantyman

Also maybe one clarification question, is your truck trying to die *at idle* at the lights, or when you hit the gas to get her rolling?

To clarify it acts like it is going to die while sitting. Everything is fine once the gas is pressed to get rolling.

[Stanco]

The soot inside the carburetor is a sign of retarded ignition timing. Retarded timing will cause exhaust gas reversion into the intake manifold and up into the carburetor. It will also cause poor idle quality.

Try advancing the distributor a couple of degrees and see if it fixes your idle issue.