How to Adjust Idle Mixture Screws

I recently upgraded the factory carburetor to this Edelbrock 1406 unit, now I need to adjust the idle mixture screws, and I show you how to make the idle happy using a vacuum gauge.
Edelbrock Carburetor #1406 amzn.to/3jey5yH
Vacuum Gauge - any generic gauge will work amzn.to/3FDKtzL
Check out me new website for parts and merch that I am selling - krusebuilt.com/
Want to help support this channel, you can "buy me a coffee", check it out! www.buymeacoffee.com/krusebuilt
The car is a 1966 Mustang Fastback with a factory V8 and C4 transmission.
Shot with GoPro Hero 8 with the Media Mod, edited on Davinci Resolve 17.
Credit for the music in the video:
::::::::::::::::::::
Epidemic Sound
Try it today! www.epidemicsound.com/referra...
::::::::::::::::::::
#Mustang
#1966
#Fastback

[@CartoonDrawingStudio]

Thanks so much Andy I have a 66 and I watch all your videos ! Great job

[@AndyKruseChannel]

Rock on!

[@timg8045]

Nice video! This one made the most sense out of a bunch that I’ve watched. 👍🏻

[@AndyKruseChannel]

Awesome, thank you!

[@eliecerrosario8665]

Very good demonstration!

[@AndyKruseChannel]

Thank you!

[@JimmyYahteez]

Great video, thank you! Beautiful Mustang and clean engine compartment!

[@AndyKruseChannel]

Thank you!

[@leeread6757]

Thanks for the video.

[@AndyKruseChannel]

You are welcome!

[@lucadesiervo2684]

Good clear info thank you

[@AndyKruseChannel]

No problem, happy to help! 🙂

[@randypascarella]

First! Thanks for this, I’ll be doing the same in a few weeks when the weather cooperates. Engine and bay looks nice and clean!

[@AndyKruseChannel]

Thanks, good luck!

[@1j007zm]

thank you!

[@AndyKruseChannel]

No problem. :)

[@mikegrotte3953]

The Best !!!

[@AndyKruseChannel]

Thanks!

[@davidklein1565]

That was very well explained thank you.. I'm needing to swap my carb (70 chev 355 Blueprint) this week and I'm no mechanic. lol wish me luck!

[@AndyKruseChannel]

Good luck, you've got this!! :)

[@darylcameron2063]

I am running a Edelbrock 1406 600 cfm on my 305 smallblock and last summer once I installed it. I marked the screws with a sharpie to know the location between the two when adjusting them.

[@AndyKruseChannel]

Yeah, little tricks like this can help down the road. :)

[@INTERNA9]

AWESOME

[@AndyKruseChannel]

Thanks 🤗

[@flyingfruitbats]

Adjustment should be incremental i.e. a 1/4 turn at a time, + other screw should be in same position as the screw adjusted. So if one screw is 1 1/4 out, the other is too. You need to allow some time for the engine to react to the adjustments before you make more.

[@AndyKruseChannel]

Unfortunately, every source I found about doing this job was subtly different from one advice to the next. In the end I had to compile everything I found and try to make it work. It did, but I was expecting people to have a different way of doing this job. No problem, I'll take everything I can get and continue to improve on my ability to work on the car. :)

[@carguyx50]

Excellent demonstration video, I feel more confident in the process now! Thank you!

[@hmayerv8]

Awesome video. I noticed your vacuum from distributor is ported. Ported or manifold vacuum, this debate seem to continue endlessly. My non-emissioned Chevy engined cars of the 70's which I owned had the vacuum on manifold and they ran like there's no tomorrow. Was always happy with them. But now, many do say it's got to be ported. I've tried ported vacuum on a stock 302 & 350 using new Edelbrock carb like yours, it idles rough and initial take off performance is not good. tried every which way to re-tune, and then ended up with manifold vacuum and everything suddenly seems perfect throughout the rpm range as we take off to cruise speeds. Back to ported again not good, back to manifold and you just love the way it goes. So what gives!

[@AndyKruseChannel]

Yeah, I've found that manifold is better too, that's what my current setup is. :)

[@grandam]

I tried ported in one of my 78 Buick Regals, and idling it runs hotter(225) than when I had it hooked up to manifold vacuum (190)

[@nursecuenca]

Great video. Im new to car scene and learning so much from people like you. So I wanted to say thanks for great content. I was wondering why you dont have both vaccum advance hose and vaccum manifold hose connected to carburetor? Just subscribed to your channel.

[@AndyKruseChannel]

Welcome aboard! Since I uploaded this video, I run my carb a little different. I don't use the ported manifold port (the port that is a little higher than the other) for my vacuum advance anymore, I use the manifold vacuum port. I made this video before I put my new engine in and I have a different carb for my new engine. After speaking to my engine builder, he recommend I use the manifold vacuum port for my vacuum advance, not the way I have it in this video. However, everything will still work with the way I have it in this video, but the engine will run a pinch leaner and in turn get better fuel economy, but it's not ideal when I'm trying to eek out every last bit of horsepower I can get. :)

[@bertramlrezenet9311]

I would like to add to your process, it is best practice to insure basic/initial timing is set to spec before you adjust the curb idle A/F mixture.

[@AndyKruseChannel]

While that is true, there's other parameters that are essential too. It's tough to put everything in one video without bogging it down. I have other videos on setting the timing, changing the jets, etc, but some times people just want a video about idle mixture screws. :)

[@FastFords289]

Great video, and great content, just wanted to let you know though that when your adjusting the air/fuel mixture screws that both screws should be turned the same amount in or out on both sides. If you turn one more than the other it is an uneven mixture and will not perform properly, but great work and glad to see you do the work yourself.

[@AndyKruseChannel]

Thanks for the feedback! :)

[@naibkhan8953]

My dear, I impress to your good advice about carburetor setting (Naib khan sourani mechanic auto carburetor specialist Abudhabi U.A.E.

[@AndyKruseChannel]

Thank you. :)

[@rjohnson6226]

Awesome video Andy. It’s easier setting my priorities to yours so I can easily follow along. Question: you mentioned headers are coming soon - are you planning to keep your pipes and mufflers or eventually redo the entire system?

[@AndyKruseChannel]

Thanks! The whole exhaust system. :)

[@rjohnson6226]

@@AndyKruseChannel I forgot to ask earlier - and I’m doing this now. I’ve seen many videos on this but if you could share any insight on priorities: should you set the ignition timing first and the set the carb? What is frustrating me most is that I read ignition timing is 6 degrees? But then I start the vacuum test and the vacuum gauge says that my ignition timing is off? So then I moved the distributed to meet the bottom threshold for a “normal engine” on the vacuum gauge and then the car idles high… any references you have to help out? Thanks! ‘65 289 w/ 4 speed top loader

[@AndyKruseChannel]

@@rjohnson6226 The timing is independent of the idle mixture screws. However, having the idle set too high can mess up the vacuum advance on a distributor and cause it to read higher than you want. I've seen and read that the timing should be 10-12 degrees, I do not recall ever reading about 6 degrees, but that doesn't mean it's wrong. I have set mine to 12 degrees, and aim for 750 RPM (with the idle screw attached to the throttle arm, not the idle mixture screws). From there you can follow the steps in this video about adjusting the idle mixture screws, keeping in mind that your idle will change. Hopefully it won't change so much that it starts to mess with your vacuum advance on the Distro and begins to add timing. I was able to get where I needed to be in this video, but I am working with all new parts. Having used, worn, or dirty parts may cause different outcomes that how it worked in this video. :)

[@rjohnson6226]

@@AndyKruseChannel thanks for taking the time to explain that. Yea, anytime I google 65 mustang 289 timing specs it returns a couple forums that outline 6 degrees BTDC. 🤷🏻‍♂️. I’ll admit my engine seems happier at 10 degrees. I’ll go re-dial it in now!

[@BPattB]

@@rjohnson6226 I know this comment section is really old but where did you end up with your timing? I bought a early 65 about 6 months ago that is pretty much complete aside from a a few things I would like to do to make it more drivable. Without going to do extreme detail about the car I know the car has a fairly radical cam and I was at 12° at idle. I bumped it to 14° and the car loved it. Just curious about your experience.

[@pjnelson8971]

Switch your distributor vacuum advance to manifold vacuum. The ported vacuum doesn't give you any advance when the throttle blades are fully closed. It will idle so much better on manifold vacuum that you should be able to back out the idle adjustment screw until it isn't doing anything.

[@pjnelson8971]

Never mind, I read some other comments, and I saw that you already changed it. I will leave my comment up in case it is useful for someone else.

[@AndyKruseChannel]

Yep, as you pointed out, I already changed it. :)

[@oliverturner5897]

Hey Andy, I’ve got a 289 Cyclone. It’s having a hard time getting started. Is there a video of yours showing how to troubleshoot that?

[@AndyKruseChannel]

Unfortunately I do not have a video about troubleshooting a car that won't start. I'm assuming it ran fine before you last moved the car, so it's not likely that something got out of adjustment. The basics are air, fuel, and spark. I'm guessing your car is getting air, so we move to fuel. If you blip the throttle linkage and see gas squirting into the carb, then you can probably rule out everything upstream from the carb. Whether the carb needs a little adjusting is a whole project in its self. For spark, you can pull a plug, leave it in the wire boot, hold it to the engine and have someone bump the starter. If it sparks, then it may be a timing issue (assuming all the other plugs aren't bad). The Points inside the distributor can mysteriously stop working (happened to me one day, had to tow the car home). I have since put a Pertronix Electronic Ignition in all my Mustangs, never had an issue with that part again, and I have a video on that. Adjusting the gap and dwell time of the Points system is tedious and I never bothered to dig into that. Although, a Points system that is not working properly may not let the spark plug do its thing, so it may be difficult to see a spark when you're holding it to the block like I mentioned above. Unfortunately, these things can be as simple as one screw needs to be turned, all the way to pulling parts and replacing them until it works again. If you're not finding anything on KZbin that can help (these 289 engine cars are more or less the same for second half of the 60s, so there's lots of videos out there), you may see if a buddy can swing by and look, or maybe ask someone from work if they could take a look. It can be difficult to diagnose a problem from my keyboard without knowing more details. I wish you luck!! :)

[@dewholdingsllc1050]

Remind me do you adjust base timing also since you were aiming for 800 rpm at idle? Does it work better with the car in gear? (Need a friend) I recall that I had to put my 5.8L HO PCM boat engine in drive, so under load, to adjust the timing and the carb for 700-800 idle range. Changing the base timing would make the idle different correct? . Been a while since I had to adjust or tune distributor and a carb engine. I’m trying to get best settings for both ignition timing and edelbrock carb.

[@AndyKruseChannel]

The timing adjustments are independent of the mixture screws and curb idle screw. The timing would be set and adjusted before tuning the carb. It doesn't matter if the car is a manual or auto when setting the mixture screws, this is just finding the best lean idle condition which is not dependent on the engine being under load. Yes, adjusting the timing will affect the idle, so it's best to set the timing first, then worry about what you want your idle rpm to be. :)

[@fuelbasti]

I tried but the gauge needle stayed stead on 17 Hg not matter how I turned the idle screws. Any Idea? Thanks for the video. Every little step helps. And do I have to close the breather on the valve cover and the PCV too?

[@AndyKruseChannel]

I once broke the idle mixture screw needle inside the port, so turning the screw never changed the idle. I had to back out the idle screw all the way to see the end of it had broken off. I replaced it with a new idle screw and I was able to adjust my idle and see a change in vacuum after that. I wonder if you're having the same issue? No, that breather on the valve cover can be open to the air (like I have on the other valve cover, with a filter), or plugged into the back of your Carb. However, you'll want to make sure you have no vacuum leaks, and that port on the back of the Carb either needs to be connected to the valve cover or it needs a cap. Good luck, you've got this! :)

[@bradlavarnway2936]

Andy, another question if I may, I read that the idle screws should be matched at the same amount of turns. for instance if you turn both in, then out 1.5 turns, then begin the process with the vacuum gauge. if you bring the right in say, 1/4 turn, you should do the same with the left idle screw? It seems you just go by the reading and don't worry about matching. (Unless you were actually counting your turns of the screw driver).

[@AndyKruseChannel]

It's ok to start with what you described, but in the end both screws will almost never be the exact same number of turns out from bottom. This is due to the subtlest variations in the carb machining, the two idle mixture screws be slightly different, and the breathing of one bank of the motor vs the other. The vacuum gauge will be the indicator you'll want for proper idle over how many turns both screws have. :)

[@bradlavarnway2936]

​@@AndyKruseChannel thank you, and I was fairy successful. I'm in the green but around 22. I did do it with air filter off. I'll keep tinkering, thanks for your reply.

[@jackmendes5634]

What if I want to run a pretty heavy cam, that is supposed to lower how much vacuum I can make

[@AndyKruseChannel]

A heavy (or "aggressive") cam will struggle at idle as it will be designed to optimize lift, duration, and overlap at whatever desired RPM range you choose. While your idle will be ruff, you'll still want to find the best lean condition as there's no point in dumping fuel while the car is idling and making essentially no power. The method covered in this video will essentially be the same. You'll want to watch the idle RPM, the vacuum on each side of the Carb (by adjusting each idle screw), and dial it all in for that best lean condition. Then, when you're done, you'll get to enjoy that awesome idle of an aggressive cam and save a little fuel. :)

[@chrisprusik6097]

I have that same tach you’re using here, when I hook the green up to the positive side of the coil the car doesn’t wanna start. Am I hooking it up wrong? Thanks!

[@AndyKruseChannel]

Doesn't it need to be on the negative terminal on the coil?

[@meanbird4979]

Can you tell me here or make a video on how to wire an electric choke? I’m having issues, thanks.

[@AndyKruseChannel]

Yes I can, the video I posted before this one was how to wire up an electric choke. :)

[@ggc87]

Question . Do u run a automatic transmisión ? If so where do u plug that vacuum line coming from it? I have it plugged to the right side of the carburetor .

[@AndyKruseChannel]

Yes, I have the Auto trans. That vacuum line you are referring to is plugged into the manifold behind my carb (I talk about it in the video where I install that new Edelbrock Intake Manifold). However, where mine is plugged in is essentially a Manifold Port, which is the same Port as the one you are describing. There is no harm in leaving your vacuum line attached to that Port, but if you move to a place where you can pull it off the Manifold, it would free up that Port on the front of the Carb for tuning. Also, some people use that Port for the Vacuum Advance line going to the Distributor. :)

[@ggc87]

@@AndyKruseChannel yeah I’ve looked it up and edelbrock has a video on the carb saying to plug the right port of the carb to ur transmission vacuum . But if it’s ok to run it thru the manifold port then I’ll take that route too! Thanks Andy enjoy ur videos . Maybe the best ones out there thanks from California

[@charlessewell1644]

Can you tell me where you bought that vacuum gauge reader at ??

[@AndyKruseChannel]

Harbor Freight. :)

[@thedobermangang3503]

its cool my brother im gonna get it put on a dyno ..all them up grades i want to feel all the power thats there..if you no what i mean..

[@AndyKruseChannel]

Cool, good luck!!

[@thedobermangang3503]

with the size cam i have what should my vacuum read...its no where near 19 to 21

[@AndyKruseChannel]

That's a great question, and unfortunately I don't have any experience with tuning a carb with a larger Cam. I know that overlap can play a role in reduced vacuum (but hydraulic rollers help alleviate some of this issue) as well as altitude. You may find reduced vacuum if your altitude is higher than mine (I'm just under 2000 feet above sea level). You might be able to find a few articles that tell you the ideal vacuum readings with that particular Cam you have. :)

[@hchzchz4682]

Andy wat tipe of spacier do you have on your carburator?

[@AndyKruseChannel]

That's a phenolic spacer, basically a fancy plastic spacer. I purchased it off eBay for about $25. There are different thicknesses you can pick from, this particular spacer is one inch thick. :)

[@VIACOMSUX1000]

so when i put it in drive or reverse the idle drops and it shuts off. any reason why?

[@AndyKruseChannel]

That's tough to say without being there. It sounds like a fuel issue, but there could be a couple things that need checked while diagnosing the issue. Things like idle mixtures screws, curb idle, throttle plate position relative to the transfer slots, accelerator pump, jet and rod size, etc. But the big thing is if your engine is dying while under load without adding more fuel via blipping the throttle, it still sounds like you've got a fuel issue. :)

[@Kpbugzy]

Can this cause the car to bog or choke ? Ex. Ill be at a red light and once it turns green , when accelerating you can feel the car choke up // hicup // or bog , once it hits a certain rpm or gets to 2nd gear itll start to run good its just everytime when comin to a complete stop

[@AndyKruseChannel]

It sounds like maybe the accelerator pump may not be tuned right. You may not be getting enough fuel during that transition from idle to part throttle. This video is only about making your engine happy when it's idling. But there could be other factors at play with your issue. Vacuum advance timing, transfer slots near your butterflies blades, fuel bowl adjustment, etc. It's tough to tell without being there and hearing what is happening. :)

[@swooshdave]

I used the vacuum gauge the last time. I was very rich at idle. This time I’m going do it again but check against my AFR gauge.

[@AndyKruseChannel]

You must have an O2 sensor in your exhaust to work with an AFR gauge?

[@swooshdave]

@@AndyKruseChannel There's a thread on VMF about it.

[@Soundofcats99]

Great video! If you set the RPM at 800 with the trans in Park/Neutral, what is it in Drive? Thanks for posting :)

[@AndyKruseChannel]

Sorry brother, I'm not going to be much help here as I don't have an automatic to prove this stuff out. I can see the value in a video explaining this kind of topic, but without an auto I can't do much. :)

[@Soundofcats99]

@@AndyKruseChannel No worries- I thought that one had the C4 in it, thanks!!!

[@AndyKruseChannel]

@@Soundofcats99 Yes, but this video is old, car has a 5 speed now. :)

[@bertramlrezenet9311]

By experience I can comment, the engine rpm will generally drop about 100 rpm. In some cases even more. There's actually no precise value.

[@Huicho417]

Great video. Are these adjustments to mixture screws and rpm done with the car in gear or in park? Thank you.

[@AndyKruseChannel]

If you have an Auto, it should be in gear. So you’ll need someone with their foot on the brake to help you work through this step. 🙂

[@Huicho417]

@@AndyKruseChannel would neutral work, or must it be in drive?

[@AndyKruseChannel]

@@Huicho417 Correct, it must be in drive. :)

[@pablobracho6653]

Calidad el motor con el carburador Edelbrock es el mejor sistema sin inyección...

[@AndyKruseChannel]

Agreed. :)

[@williamhidalgo6941]

How did you connect the RPM gauge in the engine bay?

[@AndyKruseChannel]

The Tach used the negative terminal on the coil. The other two wires go to the positive and negative terminals on the battery. :)

[@williamhidalgo6941]

@@AndyKruseChannel Thank you very much for the quick response 👍🏻

[@thedobermangang3503]

got qugot question for you ....i just rebuild my chevy 350 1990 k5 blazer i converted it over from tbi to carb ..i did a few up grade on the engine high performance intake headers 3' pipes all way back up graded the cam to a howard rattler cam 525 intake lift 535 exhaust duration 227/235 lobe separation 109 center line 103 i still the same factory heads on there i believe they the swirl port heads ..i no i should have went with some better heads but the engine was already done. i put a brand new 1406 edelbrock carb on it right out the box every sence i put that carb on there i been using alot of fuel i set the carb best as posible ..im using a awful lot of fuel just with it iding..i have my pressure regulator set at 5psi..dont no why im losing so mush fuel estion for you ....i just rebuild my chevy 350 1990 k5 blazer i converted it over from tbi to carb ..i did a few up grade on the engine high performance intake headers 3' pipes all way back up graded the cam to a howard rattler cam 525 intake lift 535 exhaust duration 227/235 lobe separation 109 center line 103 i still the same factory heads on there i believe they the swirl port heads ..i no i should have went with some better heads but the engine was already done. i put a brand new 1406 edelbrock carb on it right out the box every sence i put that carb on there i been using alot of fuel i set the carb best as posible ..im using a awful lot of fuel just with it iding..i have my pressure regulator set at 5psi..dont no why im losing so mush fuel

[@AndyKruseChannel]

It's hard to tell without being there, but if you think you're using more fuel than you should, maybe the one or both of the Rods are getting stuck open? The 1406 Carb is designed to be more fuel efficient than its manual choke brother, the 1405, and so it shouldn't be dumping a ton of fuel, especially at idle. Also, with all those mods you've done to the motor, it's possible that with all the extra air you need for the motor, you're just pulling a lot of fuel to go with it. I'm sorry Boss, I wish I could help more.

[@pjnelson8971]

Make sure that you have your vacuum advance plumbed to manifold vacuum. If it isn't, and your initial timing is set low, the engine won't want to idle. That would cause you to turn up the idle using the idle throttle adjustment. If the throttle blades are open too much, the engine could be idling on the transfer slots. That would cause all of the problems that you described.

[@bradlavarnway2936]

hello, so when you are fine tuning the Idle mixture screws, despite the numbers not mattering on the gauge you are looking for the mix to be at middle of the green section, in your case, 50? I just purchased a 67 Mustang and I am having issues with it stalling when putting it in drive, on occasions. I was told it is probably the Idle Mix. And for most, the ideal idle is 800 RPMS? thank you!

[@AndyKruseChannel]

I believe on a stock or stock-ish motor, 800 RPM is fine for idle. If you're getting idle issues putting the car into drive can be a number of issues, including a vacuum leak somewhere in the system. It's tough to tell the exact issue without being there, but not knowing if the carb was properly tuned before you got the car can play a role too. The carb could have been setup on a different car and it was placed on yours before you bought it. Someone else could have changed the Jets, and Rods, and messed with the idle mixture without knowing the effects. There can be several ways to go to get this carb dialed in. It might not hurt taking it apart and making sure the carb is clean and nothing is binding. While you're in there you can check the Jet and Rod sizes and compared them to the Edelbrock Tuning chart and see where you are. If your carb is stalling, you are likely running too lean or possibly have a vacuum leak, I'd start there and see what you find. :)

[@bradlavarnway2936]

@@AndyKruseChannel thank you!

[@zrex8911]

I didnt know sam the cooking guy had a car channel

[@AndyKruseChannel]

Me neither.

[@joseortega1114]

How to fix if your engine idling high

[@AndyKruseChannel]

Adjust the curb idle screw on the side, near the throttle linkage. Backing the screw out will drop the idle speed. However, there's more to it than that if you're having an issue with your carb and/or timing. The timing could be off, there could be a vacuum leak, or a number of other issues that is difficult to diagnose without knowing everything about one's setup. :)

[@777smitty4]

I can’t get mine out of the red stays down at 10 I have to advance timing to like 20 degress to get into the green and screws do nothing . any advice ?

[@AndyKruseChannel]

Maybe a vacuum leak somewhere?

[@777smitty4]

First thing I checked but vacuum will go up as timing advances

[@Thirdgen83]

Must be a stock cam and at low altitude.

[@AndyKruseChannel]

True and true. :)

[@63chevy56]

Thanx.... VERY INFORMATIV/HELPFUL I'm not going to like this video, but only because I don't want to be the six hundred and sixty sixth person to like it.

[@AndyKruseChannel]

Fair enough! :)

[@dennytuma]

I disagree both screws have to be the same I know on a multi carb motorcycle they won't all be the same. I never seen the big deal about a quarter turn at a time either. If your using a gauge or by ear what's the big deal. If your ever by my place I'll give you a longer screwdriver no charge.

[@AndyKruseChannel]

Can’t turn down free tools. 😁

[@l.munnier9658]

You may want to inspect spark plug to see if running TO LEAN OR TO RICH, RUNNING TO LEAN IS GOOD.

[@l.munnier9658]

Lean is NOT GOOD.

[@AndyKruseChannel]

Yes, that also helps to paint the picture of how a car is running. But this video is for idle mixture screws, I didn't want to bog it down with other details and turn this into a larger, more confusion video. :)

[@narcisoveloz2102]

You don’t even know what you are doing.

[@AndyKruseChannel]

Probably not.