Holley Vacuum Secondary Tuning EXPLAINED | Holley Carb Secrets | Holley 1850 4160 4150

[@NightWrencher]

Don't forget we are doing a 1000 subscriber giveaway! Win A FREE Holley carb! kzbin.info/www/bejne/l2a6hWZol9KZd9E

[@jacobjarvis2545]

Curious to know what happens if u have a low vacuum cam like 10 inches of hg will the vacuum secondarys open little or at all and would you run the lightest spring in the vacuum canister to make the vacuum secondarys operate

[@NightWrencher]

Well not exactly. The vacuum secondaries arnt exactly operated by vacuum. When you open the throttle past the 50% mark, you allow the secondaries to start opening but if say youre in 1st gear and you floor it, the secondaries wont open because the engine is unloaded and doesnt produce enough "suck" to open them. Vacuum gauge should only be used for idle and PV tuning. The secondaries run off their own metric

[@jacobjarvis2545]

@@NightWrencher so essentially I'd be running just a 2 barrel until maybe in a higher gear at part throttle past 50 percent for the vacuum secondarys to open if they do. Or would it be worth running mechanical secondarys

[@NightWrencher]

You'll probably be able to get into them if you have long enough gears. Like on an older 3 speed auto but probably not in a 5 speed manual. I never recommend mechanical secondaries in a street car. Vacuum secodaries run much smoother on the street even with a big cam with low vacuum. Much easier to tune

[@jacobjarvis2545]

@@NightWrencher well my 350 I built for the street and to run the 1/8th here and there. it's vortec headed solid cam long tubes full exhaust etc tr6060 six speed 4.10 rear

[@olliehopnoodle4628]

A couple of points of clarification. The secondaries do not use ported vacuum, they use venturi vacuum. The primary purpose for rod on the linkage is to force the secondaries shut, it makes sure they don't stay open even after the throttle is closed.

[@stevenbongiorno9277]

I’m watching this again. It still makes me think more about using my vacuum secondary carbs. I want to rebuild an old double pumper , and give it a shot after 20 years. Who knows. I’ve changed a lot on my engine, and gear ratio, so it might be what I’m looking for 👍

[@CadillacZachOffical]

Good video, well explained. I have a 5,500lb f100 (super cab Longbed w/helper springs) I recently built a 390 for it, went with a Holley vacuum secondary 750 to replace the Edelbrock 660 manual secondary that was on the 360 that blew up... Night and day difference between tuning and drivability. Love my Holley vacuum secondary carbs run them on all the heavy vehicles.

[@NightWrencher]

Tuning a holley is super easy which is why I really like them. I dont run anything else. Even my tow rig has a 670 vacuum secondary

[@CadillacZachOffical]

@@NightWrencher exactly, I've had great luck with them as well! My go to carbs.

[@superfuntime3107]

6:40 Do you have any actual video of the secondary's opening and closing as you have described ? Or are you just guessing ?

[@charlesoxley6503]

Thank you for the explanation i am rebuilding an old holley 4160 for my 72 f100 its got a 351w this really helped me understand that system much better thank you for your explanation of the system and the use for the smaller v8 cruisers for the daily driver👍👍

[@NightWrencher]

Thats awesome man, itll be a good carb. Hope it works out

[@b-17wingman37]

Good video ! On 460 cid , certian years , the secondary stop adjustment screw spec. is 1/4 in.

[@NightWrencher]

Yes, vacuum secondaries are very specific on that kind of stuff!

[@martebarbaro4014]

First video . Great job explaining!

[@NightWrencher]

Thank you! I appreciate it!

[@alexconan4028]

Excelent something tht no one yet explained scruw mixture on secondaries vacum

[@NightWrencher]

Thanks a bunch man! I'm glad it helped!

[@robpeters5204]

Thanks for a great explanation! That was on point and makes sense. I was wondering what the differences are when you change the springs would be? What does it do to the diaphragm? What does the harder springs do the secondaries? Does it hold the secondaries open longer or close them back faster?

[@NightWrencher]

The springs offer resistance against vacuum so the stiffer springs would open the secondaries later. Heavier/slower cars should have stiffer springs while faster/lighter cars should have lighter springs

[@randyschoolcraft6206]

What to do if you have gas coming from the shaft of the secondary butter flys on a holley 650. A 4160 carb

[@NightWrencher]

Does it drip down at idle or only starts after going for a drive?

[@randyschoolcraft6206]

@@NightWrencher idle dripping

[@randyschoolcraft6206]

Its the back one leaking is that primary or secondary running over dripping off secondary the accelerator pump rod

[@randyschoolcraft6206]

Can i send a picture

[@randyschoolcraft6206]

The car had set for 7yrs i rebuilt carb and replaced several things

[@AGClassicCarTuning]

Great video, and answers quite a few questions for me. I've been asked to help set up a supercharged Rover V8, for which we do not know the internal bore and stroke spec if they are none standard to 3500cc (213 cubic inch). No ARP studs is making me think it's relatively standard internally. The carb is a Holley 1850-2 and some have been informing me that this carb at 600cfm is way too big. However from how you have just described it running on the primary's, and will only call on the secondaries 'if and when needed' due to vacuum at the primary. Of course if the primary's can feed the vacuum requirements created without generating vacuum which needs feeding by the secondary's. Hopefully I'm right with this thinking??

[@NightWrencher]

you are correct that that carb is a 600cfm vacuum secondary carburetor. Theres a few things you need to keep in mind. Is this a blow thru or draw thru set up? Draw thru set ups will require larger carburetors because the carburetor thinks its on a larger displacement engine due to the suction. Blow thru applications would use the same CFM as an NA engine because the carburetor gets pressurized in order to get the correct flow when boost hits.

[@AGClassicCarTuning]

@@NightWrencher .....Appreciate the reply thank you. The set up of this is a draw through from a Wade RO34 supercharger. Again, as simple as it sounds I had never considered that to give positive pressure into the engine the supercharger needs to firstly fulfil the engine's normal cfm demand.....plus a bit...to actually compress the charge going into the engine.

[@NightWrencher]

Draw through superchargers are fairly easy to tune which is why theyre so popular. You gotta remember that idle and light cruise have nothing to do with booster type, size or opening. A belt driven supercharger creates power in a linear curve just like an NA engine so your engine ahould respond as if it had more cubic inches but at idle and cruise it should operate like stock. One thing about the 1850 is that youll probably have to boost refference the secondaries and power valve so it matches the incoming boost

[@AGClassicCarTuning]

@@NightWrencher .....again very much appreciated advice. I just watched a video where a guy created his own vacuum port into the chamber where the power valve is located because he wanted it to react to inlet manifold vacuum pressure instead of the vacuum created by the supercharger draw. Hence boost referencing I think. The bit that then confuses me for my background mainly with N/A cars, is that N/A cars have highest inlet vacuum at idle and this drops as the throttle blade opens. It then finally peaks again after shutting off the throttle blade when decelerating and then slowly returns to the normal level after a little time at normal running or cruise. Is this all different with a charger fitted because the positive pressure output of the charger satisfies the inlet manifold vacuum? I'm trying to get my head around the behaviour of inlet manifold vacuum which then activates the power valve during acceleration. My immediate thoughts would be to create the port in the power valve chamber but maybe share vacuum from the throttle blade port nipple which feeds the ignition dizzy advance and retard unit, because on an N/A car that is lowest at Idle and highest at WOT. Again, any advice or clarity for where I'm missing the key difference with a charger application are much appreciated thanks.

[@jwjw1213]

So I drive a 67 ford LTD with a 390 short block all stock I recently put a Holley 600 brawler on it tuned it up runs perfect until the secondaries open when they do open it has a hesitation like it’s going to stall then all at once it comes right back and the only way to get back out of the secondaries is to completely let off the gas I’m not sure if it’s a vaccum issue or something I did wrong but it’s been bothering me so any advice helps

[@NightWrencher]

Hey man, I would try a heavier secondary spring or slow down the secondary screw if it has one. A 600 is a little small for a 390 so itll pull a lot of vacuum, which is good. Hesitation might be rich or it can be lean. Put in the heavier spring or slow down the secondaries and go from there

[@jwjw1213]

@@NightWrencher will do appreciate the help

[@mandarb23]

You help me understand my Dad thanks.

[@NightWrencher]

Much appreciated! 👍

[@thehoule70]

Question I have a 355 sbc 218/220 cam around 320hp 4 speed with 3.42 I have a 670 jetted or made to be a 750 my secondary’s are only opening at 5000 rpm and on a tiny bit opening up is this carb to big for my application? I don’t want to blow up my motor help please 😮

[@NightWrencher]

Hey man, first off. You cant jet a carb and have it turn into a different CFM carb. Thats not a thing. Second, CFM size will have zero effect on whether oe not you blow up your engine. If you run it too rich or lean, that will kill an engine. As for your secondary opening, how are you checking when it will open? You can't really open the secondaries at idle.

[@thehoule70]

@@NightWrencher I just meant I bought the carb from a carb rebuilder and he said it was a 670 but he turned it into 750 iim not sure what he meant ,plus I meant that I have to rev it more than 5000 rpm to get the secondaries to open up and that If I wanted them to open up more it’ll take it to 6-7000 rpm then I would probably blow up the motor then ,anyhoo do you think this 750 is to much carb for my set up ?

[@NightWrencher]

Yeah, thats not a thing. You cant turn a carb from 1 CFM to another CFM so your carb is a 670. A 670 can get you up to 400hp no problem, its a good size for that engine. Have you verified what spring is in there?

[@thehoule70]

@@NightWrencher ohh ok no I’ll check later today is there numbers on them or just the thickness and it seems like a lot of fuel is squirting into if from the accelerator pump so I backed off the spring a bit seems to be better now

[@jsbenami]

Great fundamental explanation! I have a 4160 600CFM on a stock-ish 302 and I've been tuning with an AFR. Strong idle vacuum. After a good shot and response, descent power....rich mixture (11-12.0) it leans way out at the top of the power curve (14-16.0). Is this because I'm losing vacuum or because the metering plate is too small, and not delivering enough fuel?

[@NightWrencher]

It sounds like your secondaries are too lean. When you say good shot, do you mean nitrous? Find out what metering plate you have in it right now and see if you can install adjustible jets similar to IFRs

[@jonathanbenami902]

@@NightWrencher haha no I mean the accelerator pump shot. I installed a bigger one so there is no bogging. If I gun it my AFR will drop to 11-12 but should stay there much longer at WOT with secondaries open. Paper clip trick on the sec diaphragm shows that they are opening. But your video made me wonder how much they are opening. Anyhow yes, looks like cure is to get sec metering plate swapped to a meeting block w/jets!

[@NightWrencher]

You can buy a secondary plate that has the provisions for jets. Way cheaper than swapping to a secondary metering block

[@TheThirdWheel618]

@@NightWrencherthanks for the video I haven't seen too many videos about the secondary system on a holly it's mainly just how to set it up and to adjust the primary Jets never really adjusting the secondaries so you say that they sell a metering block that has provisions to install jets in it? Is that a Holly Part ? I did see the $80 secondary metering block that has the power valve and the idle adjustment screws or that would be secondary adjustment screws for the Jets around 80 bucks I'm not really sure what metering plate I have in it but I guess basically if it's a 600 4160 more than likely it's the same as the one that you had 74. I just recently converted over from a two barrel to a four-barrel on my 69 f250 it has a 390 I put a Edelbrock RPM intake manifold on it I bought a very early 600 CFM 4160 Street avenger I think it was one of the first that came out I know that it's basically just a classic Holly but it's not aluminum I haven't fired up the truck yet because I was doing some other things on the suspension but I'm getting close so what is the little screw underneath the the secondary diaphragm for is that for adjusting the spring or the tension on the spring meaning the tighter it is the later it will open the more l looseis the quicker it will open?

[@NightWrencher]

Some have a sort of adjuster that will help delay the opening by closing off the passage for air. The secondary diaphram that I like to use is the one with a removeable top so youcan replace the springs easily without taking the whole thing apart. The adjustible secondary plate looks exactly like the factory plate but it has holes for jets instead. If you switch to a metering block youll have to change the fuel crossover tube on a single feed or fuel rail on a dual feed. If you swap the plate, its only the plate.

[@noahsedillo]

Nightwrencher, my vac secondaries don't open on holley 750. I've been chasing this issue for months. Please help! 🙏

[@NightWrencher]

Take off your secondary vacuum pod and make sure the cork gasket is on there and in good condition. After that, push in the secondary into the pod and hold your finger over the hole with the cork gasket. Let go of the secondary diaphram and it should stay in place, if it pops out, theres a tear in it and you should replace it. Check that first and go from there

[@noahsedillo]

@@NightWrencher I've done this. Cork gasket in good condition. Stays in place while finger over the hole. I've tried all springs no change.

[@NightWrencher]

Have you tried taking out the spring entirely?

[@noahsedillo]

@@NightWrencher I actually haven't tried that. Would that open secondaries at idle?

[@NightWrencher]

No, thats just a myth. Look up "1973 charger dyno nightwrencher" and that video I actually pull the spring out on the dyno.

[@alanblaikie6398]

I have a 89 Cobra and it only shows 5" vacuum at idle, vacuum rises to 20" as i open the throttle but when on the road at very light throttle its undrivable as I think its going lean, changed all the normal stuff including power valve, could it have race cam fitted ?

[@NightWrencher]

During light cruise, the only circuits feeding the carb are the idle and transition circuit. Provided that your idle is set up right and the fuel level in the bowls is good and you have enough fuel pressure, the thing I would look for would be the size of the IFRs. Chances are they are too small to feed your engine at part throttle. Even race cams should drive down the road smooth at part throttle so cam selection isnt the issue.

[@alanblaikie6398]

@@NightWrencher Thanks for the rapid reply however all of the above in my mind is set correctly but just to try and describe what it does is difficult here goes: Engine at idle just crack open the throttle sounds good but on the road in second gear do the same thing you would be hard pressed to stay in the seat as we describe it over here "Kangaroo Petrol" this even happens on a downhill soon as you you return to idle engine goes sweet. once you give it a bit more throttle it goes ok just makes driving in town at very low speeds impossible. Shes only done 900 miles since new, manual transmission one observation is the primary throttle blades have a hole each in them approximately a 1/8th in diameter which makes the engine idle with the idle screw right off, finally what does IFRs mean??

[@NightWrencher]

IFR= Idle feed restrictors

[@NightWrencher]

kzbin.info/www/bejne/mXq4mZ9-odmDpq8

[@joesnowmobiles]

Great Explanation!

[@NightWrencher]

Thanks man 👍

[@raymondmenendez6499]

Beautifully done

[@NightWrencher]

Thanks so much! I really appreciate it!

[@josephfriedrich9792]

What benefits are there, for a screw to be in the pathway that the secondary linkage/rod travels in. Is it to convert a vacuum secondary to a mechanical? It's on a 1460

[@NightWrencher]

Yes, exactly. This is a pretty bad idea because it would allow more air in before the fuel has a chance to catch up and would cause hesitation and back fire issues. You should either tune up the 4160 so it runs how you want it or if you plan to race it, install a double pumper.

[@rosco664]

Good video man 👍

[@NightWrencher]

Thank you sir 👍

[@picco68]

Hi would love help choosing a vac or mechanical 750 for my engine set up

[@NightWrencher]

Its more about the cam than the engine size. Stock cam, 650. After market cam, 750. I always go vacuum secondary unless its a dedicated race car.

[@picco68]

Hello thanks I have a 468 Chevy with a thumpr cam only 7 or 8 inches of vacuum it's a 107 I have got a go 750, go 850 double pump from the two known places and twice different people at Holley said the 670 street avenger would be e good for street use I think the engine guy did not do much to the heads

[@NightWrencher]

The 670 is a good carb but a 750 vacuum secondary with a secondary metering block will be way easier to tune.

[@picco68]

Ok I had been looking at the 670 brawler it's a 4150 style think it has the metering block you mention but you think still step up to the 750 will look some more thank you

[@NightWrencher]

The size of the carb isnt the issue. Its the tunning. A smaller carb, when tuned correctly will out perform a bigger carb on the same engine but the problem is that most of the 600, 650 , 670 carbs have PVCRs, IFRs and jetting that is too small for larger engines or stock engines with a bigger cam. With a 750 you get larger venturies, sure but the real draw is the fact that all the tuning orfices are larger and better suited for your bigger engines so all you really need to do is rejet the carb and let it go.

[@garhpd]

Great explanation!

[@coolhandluke1503]

If I get a rebuild kit for a 4160 is it worth just getting a vac secondary diaphragm for it too, or just see if the old one holds vac?

[@NightWrencher]

The rebuild kit should come woth a new new one reguarless. I would change it if youre already in there

[@coolhandluke1503]

@@NightWrencher A good local parts supplier should include one but they want 4 times the amount I can get it online. I'm in Australia so there isn't the biggest selection to choose from and I noticed none of the kits have the vac secondary diaphragm pictured or listed. When I look at the US selection the majority are the same but some do include it. Maybe because the kits are semi universal but not all carbs have vac secondary's. Also are the vac secondary diaphragm all the same or do I need a specific one? Because I noticed the number 135-4 but not much else of a description.

[@coolhandluke1503]

Disregard that last question there seems to be a difference in rod length and I think the 135-4 is correct for a 1850

[@NightWrencher]

@@coolhandluke1503 most are the same but like you said some are different. AUS folks have a hard time getting parts so I feel your pain

[@coolhandluke1503]

@@NightWrencher Sorry for bothering you with another question, but I value your opinion. The engine I have is a modified 351c that I didn't build, It has headers aluminum intake and a bigger cam, I don't know the spec on the cam, it's not race but it's definitely not stock. It doesn't look like the carb has ever been pulled apart (but I could be wrong). Would you recommend getting some bigger jets, and what sizes? I think standard are 66.

[@trentonfree2694]

Amazing explanation

[@NightWrencher]

Thank you! I've got a ton of carb videos coming up so make sure to stick around 👍

[@MrDEEPBLACK67]

Very helpful information! Thank you!

[@jasonsimone3523]

What about the check ball? Leave it in or remove it?

[@NightWrencher]

Some have it and some of the newer ones do not. If it came with it, leave it in there. If not, dont worry about it

[@CQBWarfighter]

Definitely going to be going with a vac secondary carb for my heavy 4x4.

[@NightWrencher]

I've yet to fully tune a vacuum secondary carb so Ill be putting one on my truck too.

[@rodneyturner3197]

@@NightWrencher are these good carb for 1983 Ford 4x4 f150 c6 automatic transmission thanks

[@NightWrencher]

Yeah man, they're a solid carb

[@Cuzntime]

I have a pair of 4160 carbs on my tunnel ram drag car.. Someone told me if I crack open up the secondaries at idle it will act similar to a vacuum leak because the 4160 carbs don't have meterting blocks and idle mixture screws on the secondary side of the carb. Is this true?

[@NightWrencher]

Yes, thats exactly true. In your particular case, I would resort to drilling out the primary blades instead. Theres a video online about how to do it properly because you can really mess up the idle mixture if you dont do it right.

[@Cuzntime]

@@NightWrencher Thank you, that is exactly what I was hoping to hear.. My motor acts like it has a vacuum leak and my secondaries are cracked open but not far enough to expose to much of the transfer slots.. But if cracking them open at all will act like a vacuum leak, that probably explains the problem because I verified there is no vacuum leak anywhere else.. I have custom Quickfuel 600VS carbs.. I also have some extra throttle blades and I can get more if I screw it up but I will start out at about .100 and work my way up from there if needed..

[@NightWrencher]

@@Cuzntime I did the same thing when I wanted a higher idle without exposing the primary transfer slot but I didnt have a 4 corner idle carb, so I cracked open the secondaries and my idle went up but everywhere else the carb ran really bad. So now I just run a 4 corner idle carb but theres no room for that on a tunnel ram.

[@Welder.]

good video man, gave me ideas

[@NightWrencher]

Hope it helped!

[@joewho3691]

Great video 👍

[@NightWrencher]

Thank you!

[@erik041982]

I see I am missing the linkage now. Now I have to make one to replace it.

[@NightWrencher]

I think can get them pretty cheap online

[@erik041982]

@@NightWrencher I have a couple different zize sections of carb linkage rod my grandpa had. They use to sell stock rod you cutt it to length and bend it. They had clips snap on to ends so linkage can't fall off.

[@colinmertes5090]

I rebuilt my 750 single pump Holley it started right up and drove alright it fells like the back 2 barrels and blades are not working? It bogs down when u try to step on it hard it’s on a 350

[@here_to_watch2115]

You need more squirter. Engine masters has a great carb video.

[@colinmertes5090]

@@here_to_watch2115 blades got bent and ruined would not turn anymore so I got a new one that double pumps ⛽️

[@here_to_watch2115]

@@colinmertes5090 nice

[@BeauJones-kw7ce]

Venturi affect is what opens the secondaries, not ported vacuum.

[@TonyStark-nr5uw]

What if you put a lighter spring ?

[@NightWrencher]

it would have the secondaries come in sooner which is fine if that's what you need but you might open them up going up hills where before you could just cruise up the hill on the primaries. not a problem, but less mpg.

[@calebmartinez8771]

Thanks

[@NightWrencher]

I hope it helps!

[@jeffgodra4690]

Thanks helped

[@NightWrencher]

👍

[@rono3045]

Your dead wrong or what those butterflies are doing on the secondaries they don't flap back and forth like that when you're vacuum drops they open completely, and the reason you change those springs out is if you want the secondaries to open at a higher RPM or lower RPM. Plus you might want to get yourself a bench so you have a clean surface instead of working on carburetors on a pile of junk like you've got going on

[@NightWrencher]

You know, you're right. I did a really bad job in this video. I do plan to redo it in the near future after I finish settling in my new place. I appreciate the critique!

[@nrc17gto]

@@NightWrencher wow. Good reply. Too much back and forth these days on the internet and you handled that like a champ.

[@NightWrencher]

I appreciate it, I just believe you should admit when you're wrong. If I believe I'm right, I'll tell you exactly why, but I wont try to make up stuff just to save face.

[@DCBScout800]

what opens them if there is no vac.?

[@NightWrencher]

On my testing, I found that when I initially floor it, vaccuum stays around 5-8hg and once the secondaries open up, itll drop to zero. What I havnt checked is if when vacuum drops to zero, the secondaries continue to open. People always say a vac sec carb only takes what it needs so I'll be finding out exactly what happens at WOT

[@frankmiller9157]

Your assumptions are incorrect about how vacuum works inside of a carburetor. Vacuum secondaries do not operate off of manifold or ported vacuum, the operate off of the vacuum created as air travels through the Venturi. This vacuum is completely independent of ported vacuum, which is spawned by manifold vacuum. It's not the result of something being sucked on, it's the result of air passing over an orifice at high speed, which causes a vacuum inside of that orifice. Think about driving down the road with your window just cracked open, air is being sucked out of the vehicle by the velocity of the air going by the cracked window.

[@arcburn3364]

We shade tree ers thank you.

[@NightWrencher]

You're welcome 👍

[@mkepler5861]

great video, thanks mike

[@thehoule70]

Very good explanation

[@earldaisgomez3959]

Excellent explanation