Set & Tune Holley Carburetor Idle Mixture & Idle Speed
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- čas přidán 30. 07. 2024
- How to establish a baseline idle mixture setting for your Holley carburetor and how to fine tune idle mixture and idle speed for your application.
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For people who don’t have a older person or father in their life and has to learn everything on their own I truly appreciate people like this who take their time out of their day to show people like me how to do these types of things purchased a 84 olds cutlass with a 305 in it and holly double pumper 650cfm and learning about the things I own and in case one day I’ll need to tune it learning is always the way thanks man
Facts. No dad. CZcams our dad now days 😆
Couldn't have said it better ...my dad passed away young and never got to work on my hot rod with my dad and I miss having that but I feel he is here with me ❤
This has to be one of the realest thing I’ve ever seen. Well said sir well said 😢
This is the most accurate video I've seen. It even shows to turn the mixture screws out an extra 1/2 turn which hardly anyone knows to do. Like he said, it allows a cushion in case of a little contamination in the idle circuit. If you don't adjust that way you will be re-adjusting it at a sooner date. Customers are happier if they don't have to see their mechanic as often.
Thank you!
Having trouble today with a brand new carburetor and engine rebuild, tomorrow I am going to go at it with some knowledge! Thank you so very much for this video! I’ve seen others that talk and skim over the other two mixture screws but I wasn’t aware that they were that important.
Thank you for the time and effort. Been struggling with my Holley for quite a while. Watched the video and made the adjustments yesterday and problem solved.
Glad it helped
I just subscribed to your channel. I have to say you explained that incredibly clearly! Not too many people know about the secondary idle screw under the carb! Adjusting that screw is key to tuning idle on a choppy low vacuum cam!
Thank you...I really appreciate the kind words...
Great video and easy to follow. I'll be following your procedure to adjust my 750 double pumper👍
I really appreciate it! Check out my other videos on carb tuning too. I'll be doing a jetting and power valve tuning video (or may two of them) down the road.
Best video on tuning so glad you made this video
Thank you. Glad I could help.
Best video I’ve seen for basics
Thank you for the kudos! We work hard on this stuff! :).
Man, I never thought about opening my secondary plates to help out with the idle. I'm running a 1972 455H.O Pontiac with a nasty cam and a 850 holley dbl pumper. My idle adjustment screws are not very helpful at 1200 rpm idle.
Thanks for the idea, heading out to the shop now. Subbed. 👍👍🏁🏁
Glad the video was helpful!
Another good basic adjustment video...thank you
You're welcome!
Bang on! did it, tuned great now
Thanks! Glad it worked out for you!!!
Thank you for the video. I have the 4776-4 Holley. I recently purchased the vehicle. The carb has the 4 holes for the adjusting screws but it only has 2 screws. Did Holley make carbs with 4 holes and only two screws or did my 2 rear ones fall out. The car is running rich and closing both front screws does not shut the car off. Sorry I’m not asking for mechanical advice. I was just wondering if I’m missing two screws. Thank you
Nice video thanks for posting! What about the factory preset for the secondary idle? I'm rebuilding a used carb and would like to take it back to super stock. It's a 4781-5 and has a 50cc secondary pump with a brownish cam. Do you know if that's also stock? In the video it looks like you may have a 50cc pump as well.
Big thanks from Australia!
glad it works for you!
All great info , only thing when people hear warm the car they think 10 min idle is good take it for 15 min drive the carb characteristics will be quite different then idling for few miniutes
Excellent video. Simple and clear.
Thank you.
Nice info. Amazing how important the transfer slots are yet not talked about. Even in the Holley quick set up manual it states adjust your curb idle screw to suit your best idle.
Mine was way off. I pulled secondaries adjustment screw and put and Allen key screw so I can adjust.
Correct. The Allen screw conversion you mentioned allows you to adjust the secondary stop without removing the carb. Good idea.
@@lonewolfhotrods where can I get the allen screw conversion? Looked at summit racing...can't find it.
@@demartinsm8479 Ace Hardware, 10-32x3/8" allen head
@@rjarias1540 thanks, done and adjusted!
@@demartinsm8479 I'm curious. Did you have to make any adjustment to secondary idle screw?
For some reason when my flap is open all the way when I put in drive are reverse car stalls when I close the flap to about a pencil ✏️ width open it’s fine but bogs when driving Manuel choke can you tell me why thanks
Sorry I’m new to this and still a student. Why does vacuum change in relation to the fuel and air mixture adjustments? Is it because of the idle change?
Very usefull video! 👍
Glad to hear that!
Great video, very informative.
I have a dual quad setup with a 6-71 supercharger. How do I tune two carburetors at the same time? Do I do one and then the other?
Sale your car.
Great video
thank you!
I'm new to this. I just bought a boat with a factory rebuilt 454, 420 hp. Runs great, idles like a coal fired steam engine ( slight exaggeration ). My idle screws are seated, full in is the way I got it.
Is your video saying I should remove the carb, turn the secondary butterfly adjustment in 1 1/2 turns ? It appears to need more air. That is added at the secondaries ? Then back my idle adjustment screws out 1 1/2, then hopefully get going fine tuning.
Thanksí
That's correct. Basically, you want to open the secondary throttle plates slightly. This should provide you with some adjustability.
@@lonewolfhotrods to troubleshoot this I'm thinking before I take it off I'm going to use something to hold the secondaries open a bit with the idle adjustment screws opened 1.5 turns. Whatever I use will have a lanyard so it doesn't fall in.
The holley tech just picked up after an hour or so on hold and said likely the power valve. I'm gonna throw parts at it first I think. 🙄 Thank You !
Love the video. Need your help. Im a little lost when you said adjust each screw to max vacuum reading. Do the vacuum keep increasing with each screw adjustment or do I unhook and reconnect the vacuum G each time I adjust another screw
Glad you dig the video, and thanks for watching! I can help you out: Yes adjust each screw for the highest reading on the vacuum gauge, and then, as mentioned back them off a bit. There is no need to remove and replace the vacuum gauge for each screw. Simply leave it attached.
@@lonewolfhotrods Good morning thanks a lot. One more question. I have a aftermarket boost gauge that reads vacuum. Can I hook it up to one of the small fitting on the carb and use it. Or is it best to get one like in the video and hook up to the big one on the back of the carb
@@catfish340d You're welcome! I'd be more inclined to use the big power brake fitting at the base of the carb.
@@lonewolfhotrods good afternoon. Do you have any videos or advice on setting the Accelerate pumps and selecting jet size. If you want to connect me directly i would be glad to send you my number or email
Tks again
@@catfish340d Simply click on my channel. There are a videos on all of those topics, including one that details tuning for weather and altitude conditions.:)
You're the only video i've came across that talks about having a bigger/racing cam. i was wondering why mine never changed when adjusting i thought something was wrong with my new 950cfm race brawler, now i know & need to take my carb off and adjust the secondary screw on the bottom.
I have to run around 1100/1200 rpm for my cam in my 427 big block.
You gained a sub from me.
Thank you!
hello i have a holley 650 double pumper with 4 corner mixture screws. does the screws have to be even with each other. my primary mixture screws are 1 1/2 turns out and my secondary mixture screws are 3/4 of a turn out. this is where i get my highest vaccum reading.any help is appreciated good video.
Hi Bub...The screws do not have to be equal. Often they are not.
@@lonewolfhotrods thanks alot for the quick reply.
I have a 4160 vacuum secondaries. I previously adjusted the primary float level to where the fuel level was just barely visible (several years ago). Yesterday the float level was way too high. Is this an internal leak?
There could be something causing the needle to stick in the seat (N&S assembly). Look there first.
How do I adjust the butterfly’s on primary’s to close the exposure on my transfer slots? My carb is new out of box and they’re way too exposed
Hi Rich....First ensure the choke is "off". Then look at it again (I have a hunch the choke is "on"). Primary butterfly adjustment is the job of the idle speed screw. Just back it off if it is set too high.
Hey Mr wolf 🐺--- went through your video again and noticed something that I never heard any one say before. I have an automatic transmission, you say to put the truck in gear to check the vacuum, is that necessary? I always checked with the air filter on and in natural. Thank you for your time-----
As per the video, automatics should be placed in gear to establish the mixture and then to establish the idle speed the car is "comfortable" with.
@@lonewolfhotrods great-- good night sir ----
Is the vacuum port under the rear bowl ok for the gauge, or should I use the bigger port on the intake??
Which ever is easier.
Hello from Argentina. I´m triying to restore my 1971 F100 with an argentinian V8 292". It is equiped with a holley 2300 but they were built by Argelite with holley patent. I am having problems with tune because our numbers are not registred in Holley lists. I Think, I´m running rich how can I do to regulate this. Greetings and thanks.
My 670 Street Avenger has rear mixture screws. Only turning them 1/8 turn either way causes huge changes in idle qualilty. How would I set the rear mixture screws to the same as the fronts?
Set them independently. They do not have to be the same front to rear or even side to side.
To underscore why a vacuum gauge is one of the better tools to own, a tale of head service gone wrong...
Decades back, I had an old 350 that needed rebuilding. Guides had gone oval, a couple rockers about to punch through at valve stems, seats were pounded enough to remove any evidence of valve seats ever being cut, etc: ether required for most cold starts and plugs being regularly fouled by oil - a sad victim of unleaded gas and years of service. So heads pulled off, and away to a local machine shop. Cracked and not worth rebuilding, a set of suitable heads then got pulled from a junkyard which received all new hardware: valves, seats, guides, studs, springs/retainers, and rockers. Heads being off, great time for a new cam too so in went a hydraulic flat tappet with 224 duration @ 0.050". Fired up, and while it ran... idle vacuum was between 6 and 7". Power sucked - my engine had easily lost 50hp. Sub 10" vacuum is a horrible number for a modest/middle of the road duration obviously. Tinkered with the carb first of course [not believing new parts and a degreed cam could be so off], and that went nowhere - OFF with the heads, and lap valves to see what the shop had actually delivered: they had dropped valves in without ever doing a valve job - off the charts unforgivingly horrible work [no point in going back to get it "fixed" if that was their attention to detail], and another shop cut the seats.
Trust your vacuum gauge: sometimes a "carburetor problem" is actually something else.
Great story. Thanks for sharing!
Do vacuum secondary Holleys have a secondary idle screw or just the double pumpers?
Mine is a 670 Street Avenger vacuum secondary and it won't idle if I turn the primary idle speed screw in enough to cover the transfer slots correctly.
try bumping up your timing slightly
Hi i have set float bowls. fuel pressure 6psi adjusted butterflys as in your video. I then set all 4 idle screws to 1.5 turns, start engine have it up to temp. Adjust the 4 corner idle screws with vacuume gauge plus 1/2 turn out. Idle is very high so i back off idle screw untill it no longer touches. Still very high idle. i then back off secondry allen grub scerw untill this is no longer touching idle is still obout 1500rpm. the car is manual. I have a AFR fitted in the car. To ruduce the idle i have to richen up the idle mixture by turning out the 4 corner screws. AFR now reads 9.8 which is to rich . The idle goal is between 12.5 and 14.5. Please advise. QFT 750 SS manual secondries 34-8 metering block. i now have 8.5 powervalve which is much better for driving on the street. Phill Bain
Hi Phil. Sounds like a vacuum leak (somewhere) to me, especially since you have to set it up so fat to make it idle. If the primary and secondary throttle plates are fully closed, and it idles at the RPM level you mention, it has to be getting air elsewhere. If you have a vacuum leak, none of the tune up instructions I've provided will work very well. Aside from a vacuum leak (which you absolutely, positively must ensure is not occurring), the next thing to do is to verify the timing marks on the harmonic dampener, then set the ignition timing. Try advancing it. Drop the float level slightly. Also, power valve selection is pretty much meaningless if there's a vacuum leak somewhere. And finally (and as a last straw), the 34-8 metering block has adjustable idle speed restrictors. They may have been replaced.
@@lonewolfhotrods thanks i have tried to find a vacuum leak but no luck. Pulls 18 on vacuum gauge.
Mild cam installed. Timing set at 14 deg btdc with vacuum line plugged.
Light springs in dizzy. I will try and search for vacuum leaks again.
Thanks
@@indian1946714b did you find the problem? And was this on a cleveland? Mine idles at 1k with the idle screw backed all the way off with 12 degrees at idle
Here’s a question for you.
I have a Holley XP 750 DP with 4 corner mixture screws on a SBC.
The passenger rear screw if screwed in all the way the engine will stumble but stay running.
Same goes for the passenger front and the driver front.
But if the driver rear is turned in all the was the engine will kill.
My buddy has the same carb built by the same carb builder on a SBC and has the exact same problem.
What’s going on?
I too am struggling a bit with a Holley XP on my own car 🤔. I do not have a definitive answer for you. Keep in mind that the screws do not have to be set exactly the same number of turns in and out per side. I suspect it may have something to do with the idle bypass valve on the XP carbs though (the idle adjustment located inside the air cleaner stud hole....what a dumb place for it, but I digress).
Don't forget to set the float Bowl level first good teaching on secondary adjustment
You’re absolutely correct Paul. That is the correct order. For others who don’t know how to do it, please refer to my float setting video.
I don't have my double pumper off the engine but I have adjusted my primaries using a vacuum gage. Never thought to adjust my secondaries. Will this help with gas mileage? At this rate with gas going up I'll have to put a electric motor in my C10🤭
Hi Raymond. Any time you can get the carburetor dialed in, the fuel economy will likely improve. I suggest you check out the other videos in my tuning series (see the Holley Tuning Playlist). There's a bunch there that will help you nail down the fuel economy. And please...no electric swap!!!
@@lonewolfhotrods 🤭
What do you think is the best Holly for a 1965 GM 327? I think it has race cams but otherwise it's stock
Around 600 cfm, Chevy put a Holley 580 cfm carb on very high performance L79 327/350 hp Corvette
Ok. The engine was running extremely rich (soot on the ground where the exhaust exits the pipe---1978 Ford 460--just chugging along). Tuning did nothing and I decided to rebuild. I did the rebuild and basically have the exact same condition as before. If I turn the idle mixture screws all the way so they are seated, the engine still runs, it does not stall--there must be a leak somewhere correct? Vacuum is at about 14" and it should be about 20" if I remember correctly. I am assuming that I did something wrong in the rebuild. I've done it before, but it's been a long time. I can't think of anything else that would cause a super rich mixture like this. The float levels are fine and the engine doesn't run any differently with the idle mixture closed off, versus having the idle screws out about 1 1/4 turns.
Different camshaft makes different vacuum....If your concern about your build. Do a compression test my friend. If compression is okay. Check Intake to head gasket is correct.I would spray starter fluid at the base of the carb and see if idle changes.... If so Intake plane Flatness could be off or wrong separator plate.
@@KM-tg1mc I actually found the problem. There was a slight kink in one of the gaskets on the primary metering block. I reset the gasket and it ran just fine. I still have a vacuum leak, so I will try to fluid test at the carburetor base to see if there are any leaks there.
@@bigblockelectra Thats good my friend. Quality control is awful right now on budget intakes.I'm trying to figure out what i can do about vapor lock on my setup....Ethanol is the worst in gas. I have a wideband coming today.Hopefully i could get her going today.
I’ve got a double barrel (2300), any idea where I’d attach my vacuum gauge?
I have no idea what your application is, however some 2300 series Holleys have a port for power brakes. You can use that. Additionally, there might be a vacuum port in the intake plenum or on an intake runner. Those are typically used for power brakes or other accessories. You can tap in there.
wow well made video tyty
Thank you.
doesnt holley have a adjustable screw in the center of the carb? suppose to let more air in for idle?
larry
Hi Larry. That feature is only found in the Ultra XP series of race carburetors.
And race demon carbs
Many thanks! I have an HP750 on a 355 Chevy small block with a split pattern hydraulic roller cam. The car runs so rich at idle that it burns my eyes and throat if it idles too long.
Flip carb set the t slot , which on most holleys is around 3/4 turn down from contact , then turn your screws in until your engine leans out mine are 3/4 out on all 4 forget about this 2 turns out on all be way rich
A 650 cfm carb would clean up the low end unless your 355 is turning very high rpms😎
I tried that tip on staging the secondaries open to help with a big cam. It didnt work for me and immediately fouled all plugs
Without knowing any details of your engine/carburetor/car combination, it seems you have too much of the transfer slot exposed. Too much transition slot exposure can cause a rich idle, poor throttle response along with the potential for hesitation or stumble right off throttle. On the other hand, too little transition slot exposed can also cause a hesitation.
hello, i am trying to set up my first dual Holley 4150 set up it is a Holley hi ram intake. with a solid roller cam and trying to get the idle set right... it has the 4 corner idle on both carbs. my issue seems to be as of now. it doesn't like the idle below 1600 following the base settings of the mixture screws and transfer slots. is there a different way to set up dual carbs then the basic 4 corner set up when dealing with dual carbs ? do i focus on the secondary throttle blades to control my idle once i get the primary's set?
Hi Bob...What is the manifold vacuum reading?
@@lonewolfhotrods 12 inches @ 1500 rpm and base timing @ 15 btdc
it seem to like 20 degrees timing better and runs cleaner but it doesn't want to idle down i got the seconderys closed and mixture screws on the secondary's blocks closed as of right now to just work with the primery's. its a freah build 414 cubic inch sbf 12.0:1 comp 255/267 duration @ .50
any help would be great thanks.
@@quick-performance-services Hi again Bob. Do you have power valves in the carbs? Check out my video on Jetting & Power Valves. Additionally, you might want to try adjusting the secondary idle screws (under the carbs). Opening the secondaries can definitely help.
@@lonewolfhotrods yes I have 6.5 in all corners
I'm working on it now it seems I got it to idle at 1200 rpm but it idles up and I have to push the linkage down with my hand
So I need to address that first
update: got the linkage figured out had it binding up between carbs. dropped the primery's down and used the secondery idle to adjust idle speed got it at 1300 rpms while running 21 degrees btdc and keeping vac. around 11 inches. the vacuum seem to float a bit after it idles for a min wondering if its leaning out ? would changing the air bleeds from 75 to say 73 help with that issue? thanks again for your time. ill check out your vids..
Does a cam of 528in 538ex 221in/226ex duration @50 050-110 degree lobe separation need secondary drew re set
I really can't answer that. There is no cut and dry answer. It all depends upon the engine combination, how the engine is currently idling and more.
@@lonewolfhotrods I have car running 32 total . having trouble with vacuum it dances between 10 and 12 idle screws are having little effect carb Holley. 4160 duel feed vac secdery 600cfm should I try opening secondary a bit
@@kenschreiner6465 Yes, I would try that.
Where do you put the vacuum hose? Small or large port.
small port on bottom front of carb base
The last part confused me. I fine tune it, lower the idle, then turn all the screws out another 1/2 turn?
I tried that and my engine is too rich, ran best tuning 4 corners with a vacuum gage, mine is a 383 Chevy with Holley 670 street avenger with all 4 mixture screws set at 3/4 turn out from full bottom and its very sensitive to any more or less turns on screws.
Can i use vaccumm gage in That port of the carb base?
yes, the small front is for a vacuum gage
Do you have all the screw the same number of turns?
No, they do not.
Can you adjust screws on the carb with it installed
Yes. That’s why a vacuum gauge is used - engine running.
Lone Wolf Hot Rods k thanks
Where did the vacuum line hook to carb
try the power brake port at the back of the carb (the big one on the baseplate).
I have a two barrel carb
I'm
My small block C2 says 'thanks'
You're welcome!
All the precise idle mixture screw adjustments with the vacuum gauge. Great. But then you open all 4 corners 1/2 turn? Don't I want the best idle mixture for response, performance and MPG? I love your video but don't understand the last instruction for the additional 1/ 2 turn open. Thanks
If you watch the video again, you'll see that step, and the rationale behind it is explained. Basically, tuning with the vacuum gauge will provide you with a relatively lean idle mixture. Enrichening it or "Fattening It Up" slightly will provide you with a cushion from "too lean".
My head is spinning ..i think ill just buy an Edelbrock carb ..this is all greek to me and no wonder i was never good at carb adjustments for the past 40 years