Holley Carb Vacuum Secondaries NOT Opening? - 5 MIN Tested/Explained/Repaired

are your holley vacuum secondaries working? here is how to test them in several different ways

[@Electricday27]

5 years ago and I still appreciate this

[@jeromecarter139]

I would just like to take the time and thank you for explaining all these holley tricks, I've been monkeying around with a few holley carbs for my 86 Ram, and watching your videos has helped me get it to run great! thanks so much!

[@ThunderHead289]

thank goodness i am not doing this for no reason! appreciate the positive feedback!!!

[@montepatton9040]

You sir are awesome. You just doubled the onions my old truck had. Thank you so much for all your content. Truly enjoy watching you and when I saw your video listed about the vacuum problem I had on my card I knew it would be worth the watch.

[@bobstephens8851]

I was always afraid to try a vac secondary Holley because I could never tell if the secondaries were actually opening. I might try one after watching this!

[@markschmitt5550]

I prefer a Vacuum Secondary carb in most cases. The low end is crisper and you have more control over the mid and top end. The two piece vacuum pot top should come as a standard feature, although most of the new carbs that roll off the line, are already flow blench tested and setup for most applications, if... you pick the right CFM size. Placing a 750 on a fairly stock small block won't give you the best performance. You need to follow the guidelines and you'll be rewarded with a great driving experience. I am unfamiliar with the Summit Carb that you have there... It looks like it has a one piece fuel bowl with a removable top? Does it take standard Holley Jets and Power Valves?

[@ThunderHead289]

yes! it is actually made by holley with a summit brand slapped on it. it is all the same stuff as a holley, EXCEPT the accelerator pump. the annular boosters are a ford 4100 style unit with different accelerator pump jets which is different than the pump nozzle. outside of that, everything is holley.

[@markschmitt5550]

Cool... I'm currently using and in love with the Street Demon which is a Holley product... I will have to give the Summit carb a go on my next project. I like the one piece fuel bowl idea; no leaks. Yes ago, like the late 60's and early 70's, my experience with the Holley carbs was temperamental. Most everyone hated them because you couldn't get them to stay dialed in. Many of us ran modified Qaudrajets, Carter AFB, and Thermoquads. It's nice to see better carb options available now. Thanks for your video, too!

[@robertclymer6948]

Thank you Luke for explaining this and showing exactly what you are talking about. It is crazy, but you videos always seem to address exactly the issues I am having. Weird. Appreciate you Brother! Thanks!

[@sheldonbaxter9558]

I have an issue with my Holley backfiring during higher rpm’s. At idle the carb runs fine but when I get around 2500+ rpm’s she starts to backfire. Any ideas on what may be causing this?

[@user-gy7tt5bh2n]

On a three or four g how do you set the straight when you pull it out and put a new one in

[@peggyparrow2059]

They make a little tool called a mini vacuum gage pump, which is also Good for checking for blowen power valves. Its cheep insurance.

[@joesmith-fi1sx]

will the secondaries open when you are parked and revving? either by hand throttle or gas pedal? yryibg to figure out if mine are opening on my 440

[@jasonjoncas5998]

Also the Holley quick change you can change springs on the carb.

[@jorgenlinne4183]

?

[@D_Snapp_Garage]

Am I crazy or is that Holley vacuum canister you show backwards movement from normal? Why is it extended with thumb plugging the port, then pulls in when you released it?

[@phw340]

Nice video and clear explanation of how the secondaries work! Thanks!

[@Threshold2012]

How is it your Holley pulls up in the normal position? Mark 4:30 in the video. I have the exact same one with the quick change, and the spring is on top, so it pushes the rod back out to full extension when there is no vacuum. Normally you push the rod in all the way, put your finger on the hole, and if the rod stays in, the diaphragm is good. Release your finger, and the spring pushes it back down

[@D_Snapp_Garage]

I was wondering exact same thing! I've had a few whiskeys tonight but not that many haha @thunderhead289

[@chrish5096]

I have a Holley quickfuel 450 cam carb on my ford 300i6 and was having this issue, and turned the adjustment screw almost all the way in, my secondaries are opening now, but only abou half way. Any ideas?

[@55chevytruck]

When you are idling you should have the most vacuum and it drops when you are opening up. Vacuum is holding the secondaries shut and when it drops they open. That is how I always thought of it.

[@ArdFarkable]

it doesnt go off manifold vacuum. it is from a tiny hole in the bore, that gets suction like the venturis do. so at idle/cruise it gets low suction because of low air velocity. and when the air velocity is high enough inside the carb barrels, THEN it opens to provide more air, basically right as the primaries are max cfm. That way you always keep high air speed through the carb no matter what. You can floor it, which kills your vacuum/air speed, and the secondaries will not open.

[@noahsedillo]

Thunderhead289- I have a holley 750 and my vac secondaries never open. I've tried a million different things and have been chasing this for months. Please help! 🙏 Also there is gas leaking down the shaft of the linkage going to the diaphram cannister.

[@JRingo-hn9fu]

Rebuilding a summit racing 600cfm carb, trying to find out where the two check balls go that come in rebuild kit? Any help would be appreciated.. A small one about the size of a B.B. and a one half the size of that. I’m assuming one goes in under secondary vacuum diaphragm..

[@jimmcgill3109]

Thank you my friend.....your videos are some of the best on you tube

[@ThunderHead289]

+jim mcgill i wouldnt say that, i just try to simplify things. i appreciate the positive feedback. ill just keep on recording when im working on my junk iron !!!

[@jimmcgill3109]

I have a 63 f100 iam working on , top speed is 50 mph sucks .....don't know what gears I need .....I was thinking 355,maybe they are to tall

[@ThunderHead289]

+jim mcgill that's to the floor? What rpm are you bumping at that speed?

[@jimmcgill3109]

its on the floor...63 223 in line 6 four speed I have to let of the throttle rpm maxed out

[@ThunderHead289]

dang, i think some swaps are in order!

[@williamcharles9480]

I like to add a little info. Not all of those secondary diaphragms are the same. Make sure that the shaft length is the same because even though diaphragms may look identical, the shaft length can be different from one model carb to the next. Another thing is the Holley quick change kit for the change out of the secondary spring, as shown in the video, will fit on the vacuum secondary Summit carbs.

[@ThunderHead289]

I should have mentioned something about the length I agree. Yes, the Holley indeed found its way onto my summit in my truck.

[@williamcharles9480]

ThunderHead289 You can't think of everything at one moment. Thought I help you out a little. I really appreciate you taking the time to do your videos. You cover a lot of stuff that doesn't get discussed very often. This info that you pass out is a big help to a lot of folks including myself.

[@ThunderHead289]

i try to cover things in detail so people dont have to learn the hard way like i did. i appreciate the positive comment.

[@williamcharles9480]

ThunderHead289 You've got it, my friend. All of the best.

[@rscam1968]

i have a summit on my 350 and the last time i started it the car started fine with the fast idle ,,gave the pedal a quick tap to knock down the fast idle and now its running bad and wont idle unless i turn up the idle ...

[@Tom-wq2mz]

1460 Holley. Off the car pulling linkage arm back first two open and back two doesn't. Front and rear secondarys should open correct?

[@Gleanerman78]

Hey Thunderhead289 quick question I just put a holley 600 vaccum secondary on my 355 sbc, it runs awesome good response but when I try to pull it up over 4500 it starts popping and falls on its face until I shift then the power comes back I'm stumped any help would be greatly appreciated thanks

[@chrismaciel355]

Hi thunderhead just wondering do you like the vacuum secondary carb on a street vehicle with a manual trans? Have you ever done a comparison of vaccum vs mechanical on a street engine? I'm looking to buy a holley but still unsure which one. I'm use to eldelbrock.

[@No-vm7go]

7:11 Your 'POS' farm truck daily driver runs a lot better than mine ;-)

[@bluejayshatrau]

Hey Thunder I am having problems with my 4160 Holley on my 1976 f250 with the 360. When i puts a with load on the engine from idle it wants to act like its dieing but if i easy into it, its fine. im stumped right now. swapped from a 2150 motorcraft carb and intake to a 4150 carb and some dump truck intake.)

[@joeybrewer6564]

justin shatrau is your accelerator pump working?

[@jesseg573]

Whats up bro, i have a question i have a 750 cfm demon carb whenever i floor it the gas stays full accelerated its not the pedal cables it’s something with the choke

[@jesseg573]

Any thoughts ?

[@arvinjessee-zx4mc]

My holley doesn't have that diaphragm

[@victorjohnson7512]

With aftermarket camshafts, there may not be any vacuum left.

[@ThunderHead289]

Not how that works - secondaries are opened by venturi vacuum which increases with throttle vs manifold/ported vacuum

[@superfuntime3107]

1:23 That was not 5000 RPM.

[@huntergarrett4556]

Did you have to do anything special to the carb because it's a manual

[@ThunderHead289]

not at all

[@ryanzimmerman1240]

How far should the bar move? My paperclip was about 1/4-1/8 inch down

[@ThunderHead289]

Look down the throat of the carb and open the primary throttle - this allows you to now be able to open the secondaries. Measure how far the rod has to go for the blades to be fully open 👍

[@dickeymoore4264]

Does the rear bowl have squirters like a double pumper that works with vacuum on vacuum secondary carburetors?

[@ThunderHead289]

They do not - they open much slower than a DP would, so it isn’t needed. A DP will always outperform the VC on the track

[@dickeymoore4264]

@@ThunderHead289 so why is there a rear feed secondary fuel bowl on a dual feed Holley if I may ask you?Thanks

[@ThunderHead289]

I’m assuming it’s just a modular design - there are boosters in the rear where when the secondary throttle blades are open flow fuel. When you say squirters, you are using terminology reserved for the accelerator pump discharge nozzle tip, which a vacuum secondary does not have a secondary accelerator pump.

[@dickeymoore4264]

@@ThunderHead289 okay Thanks

[@FamilyMan1]

Why is your electronic choke not connected?

[@ThunderHead289]

I typically don't use chokes and adjust them wide open to disable them. At least electric chokes - manual chokes I'll leave as is.

[@FamilyMan1]

@@ThunderHead289 OK I'm following...how about cold start? Sorry for the questions I'm just new to the carb game

[@alexv.100]

Dont vacuum secondary controlled carbs need vacuum lines to run smooth/ ideal?

[@ThunderHead289]

The port that opens the vacuum secondary is drilled into the venturi bore - it’s small, but can be seen when looking down the throat of the carb. As air speed increases via RPM, venturi vacuum increases - when the draw is stronger then the secondary spring, it secondaries begin to open.

[@alexv.100]

@@ThunderHead289 I'm still learning about carbs. I guess the guy that upgraded the stock 2Brl carb to a 4Brl just left them on just in case, before I bought this fox.

[@ThunderHead289]

I don’t follow. Left what on?

[@alexv.100]

@@ThunderHead289 sorry, all the vacuum lines. Ive been slowly repairing/plugging them up.... guess I can just rip em out

[@stupidman9774]

hey thunderhead. do you know how to convert the 4160 to full manual secondary

[@ThunderHead289]

Stupid Man generally something you want to avoid since you don’t have a secondary accelerator pump - you will have a large flat spot. But if you really want to, a sheet metal screw in the linkage to force it open does the trick.

[@glennmanchester9151]

You didnt get the burnout callout ??

[@ThunderHead289]

No one ever once said “Thunderhead289”

[@Wildstar40]

I like the mechanical secondary system. Faster response and way more reliable. The paper clip made me laugh, I just fire it up and hit the throttle by hand under the hood a couple of times when it is warmed up and watch the vacuum advance with my eyes, no road test needed. But the paper clip did make me laugh.

[@HorsepowerGarageVideos]

Vacuum secondaries will only open under load, that's why you have to use the paper clip and drive it.

[@714xoc5]

What would be a good source for vacuum for the secondary should I use intake vacuum or brake booster vacuum this for a 84 fox body still learning this carb stuff

[@mikehenry4743]

I know it's an old post but your vacuum signal for the secondaries is internal you don't need to hook up a vacuum line.

[@maynardreed4036]

Personally I prefer mechanical secondary carbs myself.

[@shawnh.2334]

ya, i'm thinking the carb on my nova isn't working properly. Just got it a few weeks ago.

[@ThunderHead289]

What symptoms are you having?

[@shawnh.2334]

its not revving past 4000 rpms. has a shift kit but only smokes the tires if you power break it. i havent owned a carb car ddo its all new to me. the guy weejo owned it only drove it a mile to work so i figured the carb is dirty and not running optimally. i shot it with carb cleaner but havent adjusted anything.

[@ThunderHead289]

when you get ready to adjust, send me a message. there is a lot to be learned here and i will do my best to point you in the right direction. you will need a vacuum gauge and a timing light. failure to have things adjusted properly can lead to engine meltdown. hit me up at [e-mail]

[@shawnh.2334]

cool. right now im just fixing things here and there. i bought headers. installing carpet

[@ThunderHead289]

gotcha. keep in touch.

[@jameslutz3116]

6.07

[@ThunderHead289]

what about the picture?

[@jameslutz3116]

+ThunderHead289 didn't know that was where the port went to! I just changed to the Demon carb! subscribed to your channel! good information, thanks!

[@fume_youtube]

Damn you are not rowing thru gears you rowing a boat