You may not see this so many years later but this was a huge help!!!!!!! I’ve been searching forever for someone that cares about what vacuum ports do what!
You have no idea how you just saved me and my ol girl. I wish i had you as a friend. I have been searching forever for something like this.. mine was hooked up allll wrong.
Thx for taking the time to post this content. It popped up when I was researching vac lines on an old motorhome I took apart months ago for a quick fix, and then got sidetracked and forgot what hooked where in the time between...lol
This is 101 auto mechanics. I have two carbs one for my 76 GMC truck restore project and 84 van. I learned more here than I learned in any book I seen so far about vacuum lines.
I recently rebuilt my '89 Olds 307 as a student auto tech project (idiot, I know) and since the c-virus, the project was paused mid-reassembly in the vehicle. Once it got it back home and put everything back in the engine bay, I missed a port on the the carb and it didn't run right. Since it's been months I couldn't remember what went where, even with marked vacuum lines. This explanation helped identify and confirm my carb's setup and now the wagon runs great!
You saved my life again. After watching this video i went and rewired the vaccum lines and vala, no more hesitation at idle or accelerating from dead stop. For me the distributor vaccum was not connected to ported vaccum so i fixed that and the back vaccum wire was not connected to the Air cleaner port. Thanks for the video
That extra port usually has a diaphragm that acts as a brake on the secondary air flaps and makes it open smoothly and sometimes there are two that slow them down when closing like you said to prevent flutter. I had an 850 3 ring primary Venturis. Ford 429CJs used a similar carb but they had a Chevrolet type fuel inlet that went to the side. The BOP carbs usually have straight in the front. The only weakness about the QJet were the well casting plugs needed a thin smear of JBWeld around them and it has to be thin or you can crack the body or throttle plate. If they seep you will notice heat soak. Also when the throttle shafts are worn from having too heavy a spring and you get a vacuum leak, they are done, get another carb. Holley made a good solution, the one piece Autolite style 8011 Spreadbore. They are great carbs , better than the 4165 spread bore. Once the QJet gets a vacuum leak in the shaft they are so lightly made, good luck ever trying to bush it. Ask me how I know.
THANK YOU THANK YOU THANK YOU, I've been building a 75 eldorado for about 3 years now EVERYTHING is new from the ground up but I just could not figure out the carburetor. In my defense I was never much of a car guy growing up lol but building this car I learned alot and I searched RUclips for months and right when I was about to give up I stumbled upon your page and finally got a great break down. So like I said before THANK YOU THANK YOU THANK YOU
First,I want to say your q-jet videos are great.I've enjoyed them very much! One disagreement though. The factory setup for my 79 TA's with Olds 403's is manifold vacuum going straight to the vac advance using the upper right manifold vac port. Also, in my 70's and late 60's factory service manuals, most show manifold vacuum.So, the assumption that ported vacuum is always used for the vac advance is incorrect.My engines run stronger and cooler on manifold vacuum.Thanks again for your vids!
Thanks for taking the time to post this.Official chevy light duty truck manuals dont show this.Sure they have vacuum diagrams but most vehicles with a quadrajet are over 30 years old!Thanks again!I was able to make my 1985 g20 van with esc use a 1980 quadrajet after I disabled the esc computer thanks to your video!
no, that's the fresh air source for the heated choke. The nipple on the carb isn't a vacuum source. It provides filtered air that is then drawn through a metal line to the plate on the intake(which actually has another metal line inside the intake) and then back out through a short line to the hot air choke.
Hey Tyler. I'd like to thank you for taking the time to make the videos, and supply those of us who aren't as knowlegable as you and thanks, while I'm at it for putting it in a manner that common people can understand .carbs have always been a pain in the butt for me. I watched all your videos, a couple of them a few times. but when I got the carb back on the 1976 k20 camper special and turned the key it fired right up and purred like a kitten! I was amazed, I was happy, and thankful to you for taking the time to help the other guy. maybe I can share what I learned from you with someone who is stuck like I was. thanks again for doing what you do
@Razastar1971 You can cap off whichever ones you don't need. Whether or not you use vacuum from the carb doesn't affect it's operation in any way unless you leave off a cap and cause a vacuum leak.
Thanks doing my first and last carb. Im learning things only do once. My 77 RV 455 olds. Needs carb redone its the original. When you first look at them they look intimidating. But after watching good vids like yours 10 times im ready to try.
Thank you SO much.I have a 1979 Chevrolet G-20 Van that was built for 80 and apparently has a Quadrajet made by Carter for GMC but has a lot of simularities to a thermoquad as well being made by Carter. I'm having to go back and redo the vacuum system and also make room for other stuff. I have an expansive shelf of different carburetor manuals and shop manuals and none of them hit the nail on the head like this video. I had nothing to go by but feel and this nailed every port on the front i had questions about (specifically for the EGR and Charcoal vent) I'll have to take pictures or video on this thing cause its a frankenstein carb in design. THANKS! :D -Foxi D'elegance
At about the 10:35 mark of this video, we always called that vacuum pod the choke pull off, if it's not working properly, the engine will not run properly, because it's choking itself to death using more gas, it may even cause your engine to have a miss, you'll also have excessive black smoot around the end of your tailpipe, I can't even begin saying how many choke pull-offs I've had to replace during my mechanic career. The front vacuum pod is what engages the choke, and the rear vacuum pod disengages the choke, they're designed to work together, along with the divorce manifold heater coil. If your secondaries doesn't open when you floor it going down the road, there's a very good chance your choke pull off or something within the choke setup is the problem. I personally think that the Rochester Quadrajet 4-bbl 750/800 cfm carburetors are one of the best designed carburetors ever built. I've heard so many people talk bad about the Quadrajet, but like anything else, you gotta be smarter than the equipment you're operating. I'm a retired mechanic, but even during my working days, it didn't matter if I was working at a GM dealership or independent auto repair shop, very few mechanics actually knew how to properly rebuild and or tune a Quadrajet 4-bbl carburetor, yet they're so simple to understand how they're designed to function properly. I'd take a Quadrajet carburetor over a Holley, Edelbrock, or Carter anyday for a stock engine up to a moderately cammed and or modified street engine that'll turn 6500 rpms, it mostly depends on what camshaft will be used in the car and or engine, Holley would be my second choice.
Some Buick Olds Cadillac QJs use both choke pulloffs in a staged setup where the front one opens the choke a little right away. Then the rear pulloff opens it more a little later due to the restriction built into it's vacuum fitting. This has the effect of enabling earlier choke opening to cut down on cold engine emissions. That little restriction also has a bleed in it to let the pulloff modulate the choke spring tension. Early QJs had only a single front pulloff made of plastic.
Well, that's all they ever have. It won't hurt anything to share the one vacuum source, but keep in mind that GM's of that vintage including your Olds ran the ported vacuum signal through thermostatic vacuum valves that would not permit egr or distributor advance until a certain coolant temp was reached. It was purely for emissions, but if you wish to have it like it originally was, you can google 1976 Olds vacuum diagrams and search the "images"
Great video. I have a Q-jet that has a threaded hole where you have a nipple connection that you said was for the distributor vacuum advance. It's on the front that is to the right of the fuel input and half way up the carburetor. My vacuum advance was connected to the small one on the front bottom right. What do I do with this threaded hole to make the connection to my distributor? What type of threaded connection do I use? I also have the threaded hole on the back for the power brakes. I have manual brakes but I want to convert to power. Where do you get the fittings for this as well? Thanks.
H WhoSaidTyler, Is there any way to remove all these vacuum hoses? i remember on edelbrock i only had the vacuum from the dristributor and the fuel lines. Rest were tapped. Thanks
Tyler, my-quadrajet-go-to-guy, I've got something that's got me perplexed on my truck. If it helps; it's an 81 GMC c3500 2wd 350/th400/4.56:1. The carb is a 17059216....you know the kind 😁 As far as I can tell everything is dialed in damn well. The idle mixture is nice, idle is 650-700 in park with vac disconnected. It drives 99% perfect. I've got a little problem in my timing. I've read the stock vac advance pulls too much on these and that seems like what is happening BUT I think the source might be the carb. ***Ok here's the question: should there be ZERO vacuum at the ported port at idle? As you say in the vid from **3:45** to about **5:45**? *** I have a pretty strong vacuum signal there. I haven't measured it. Base timing is 8 degrees. When I connect to that port it rises to 20 degrees. And, if I go to strait manifold vacuum it'll rise to 26 degrees. All these numbers are at idle. If I back the idle speed screw out any more or fiddle with timing it will want to die out.
I have a 1983 chevy g 30 van with a small block 350 and quadrajet 4bbl carb . I have a question ; Why does my timed vacume port have constant manifold vacume instead of timed ? I was not aware that the quadrajet was manufactured with the carb having no timed vac port snd the tyipical timed vacume port having manifold vac
Could the port on the carb on the back side be used for the th400 vaccum line??? Also where else can that vaccum be take from? Thanks for the video.....was looking for some explanation for a Rochester. Very informative!!
What about the vaccuum line at the rear?? Is it for the brake's power booster?? Mine has been cut on an E4MC from '81. How do I extract the crimped line for then to plug a new metal pipe?? I want to reconnect that line again into the power booster for the brakes.
Hello Tyler, came across your video great info. I put a newer carb (1985) on my old motor and find i have vacuum all the time on the what used to be ported vacuum port. I'm assuming the car it came off had some emissions, TVS, vacuum delay or check valve on it. How do I correct this? any help will be much appreciated
a while back ago, i was fixing on my cutlass. and i broke the line that screwed into that big circle thats right in the front of the carburetor. can you tell me what that big circle screw in is for and what line that is? thanks brotha.
Tyler, can you please help me? I have a quadrajet and it's on a 455 toronado from 1974. I'm going to utilize your fast idle adjustment because I feel mine is high but the problem that I'm having now is from an idle once the vehicle is warmed if you barely depressed the gas pedal, it bogs down and sometimes stalls if you hold it but if you push it further it will work its way through the bog and the RPMs will raise fine. What is causing this initial bog? I've watched your videos but can't seem to find one that covers that early bogging off idle. There are plenty of videos about Holly carbs doing that, but I can't find any on quadrajet. You're wonderful!
thanks to you ive corrected some errors, i only have 1 port that vaccum exists at idle and it was hooked to the distrubutor valve 0_o now i have everthing that looks like a egr hooked on a ported valve. the heater unit i hooked to the idle vaccum port. at least i think its the heater unit bcuz it used to switch the interior vents faster when i was on the throttle, now it switches fast all the time. my bouncy idle was also reduced as well, i think it was making it hard to set the mixture. my brake booster has its own port on the manifold so im good there. my pcv was hooked to the factory filter case but it was before the filter and my edlebrock air cleaner has the pcv hole AFTER the filter so i left it off with a tiny pcv filter on it. its temporary as im trying to rig something to mount it on and before the filter. thanks for the help
I have no laws concerning emmision testing and I just want to get the car started after sitting 20 yrs. What do i need to start it. I know i need fuel but what else.
everyone i know with a quadrajet including myself runs manifold vacuum for distributor advance. everyone around here believes that to be the best way to do it. is there any advantage to port vacuum advance on a k20 i daily drive and tow with with a stock 350ci and sm465?
Thank you so much for the information. I don't understand very much english but please correct me if I'm wrong. Distribuitor advance is conected at the ported vacuom in driver side fron front of the carb. I miss were to conect the shock line usually goes into the intake, my intake don't has that hole and I'd like to know if is posible conect it at any other vacuom.
Sir I have watched all the videos that you have posted about the Quadrajets. I am a Novice Mechanic. I am working on a 86 Chevy Monte Carlo. On the Quadrajet that I have I am referring to the Vacuum breaker. Even after the engine reachs operating temp. The Vacuum breaker is not releasing Vacuum to allow the Secondaries to open at all. Do you have some helpful advice for me so I may fix this problem?
The vacuum break stays engaged until the vacuum signal goes away, which happens at full throttle. If you hook a vacuum gauge to your engine and position it where you can watch it as you drive, you'll see that normally there is about 15" of vacuum at idle and light throttle. The heavier the throttle application, the less vacuum available. So, that vacuum break is working. You just can't see it because it's hard to rev the engine that hard standing there to get to zero vacuum. I suspect there may be something else preventing the secondaries from operating, but not the vacuum break.
I stumbled on to your videos last night and watched every one I could. I have learned more about my carb than any books, websites or videos that I have seen in the past 12 years. I've already put some of your teaching to use. (I was one of the guys that had those back butterflies so loose they almost fell open) One question: Everytime I step on the gas my car hesitates for just a second, like a dead spot. what causes that? My carb was "pro" rebuilt a couple years ago and has always done it.
I posted info on your video. Let me know if you need more help. I forgot to mention that if there's a choke pull-off on your carb, and it looked like there was, it connects to a MANIFOLD vacuum source.
So what would you do with the charcoal vacuum connection on the carb if you're not running a charcoal canister? Do you just block it off? Does it need to be vacuumed? Rat rod application...
Leave it open to the atmosphere. Otherwise it could cause hard starting from vapors having nowhere to go except inside the air cleaner. If you want to be fancy you could glue a small piece of microphone foam over the end to keep the dust out.
Thanks. I'm gonna put some kind of breather filter on it. Maybe even just a fuel filter open on one end. Now I have to figure out a kick down system as the carb came off a car with a th400 and my set-up is a 700r4. Oddly enough, the carb has a strange "screw on" linkage plate attachment on the end of the primary shaft. So I'm gonna take one with the th400 tv cable hook up, match it with a set of holes like the linkage plate that's on it now and screw the new one with the tv link on like the one that's on there now... Otherwise I'll have to change the entire primary shaft. Those butterfly screws are a bitch!
Ive watched all your videos on the Rochester (several times). Can you do a video on how the linkages are connected behind the choke? My secondaries arent opening correctly and I believe the linkage behind the choke isnt assembled correctly and therfore the "stop lever" on the secondaries isnt connected/operating correctly. Also, the air/fuel mixture screw on the choke side of the carb doesnt have any effect on the idling when I turn it in either direction. The mixture screw on the drivers side ( or closest to the idle screw ) works fine and theres an obvious idle change when I turn the screw. Whats up with the choke side mixture screw not changing the idle when turned fully closed or fully open? Thanks!!!
Sure. Could you provide me the carb# stamped vertically on a rib on the driver-side of the carb? As far as the mixture screw not reacting on one side...I bet you know the answer but don't KNOW you know it...so I'll test you: if one side of a faucet works and the other doesn't...or...if a vent on one side of the dash blows air but the other side doesn't, what would you suspect to be the reason? Same principle in all cases.
WhoSaidTyler Yep! I cleaned the idle mixture screw port and its working properly now. Unfortunetly I have an oil leak from the head gasket so I need to get that fixed this weekend. Someone scratched out the serial number so im stuck with what Ive got. Its an electric choke carb which was all rebuilt and very clean. When I removed the carb the lower secondaries open just fine. I noticed the. "stop lever/ stop tab" is just dangling in place though. The choke linkage does however touch the stop lever when on full throttle and releases the stop lever so the secondaries open. After releasing the full throttle the stop tab doesnt have any tension on it and can move freely.
I had a question I have a 74 Buick Electra with a 455. And after doing a top end rebuild I forgot where all the vacuum hoses go. And for the life of me I can't find any diagrams for it. Do you by chance know how they are routed.
Hey Tyler. You are awesome. Thank you for your videos. I have a 350, with a Rochester Quad on my boat. Recently I had a lot of work done to it. I went out the other day and it started right up, motored great at idle and low RPM. When I went to punch the throttle, I had half the power I should have. It felt fuel starved. Now I am confused. Are the secondaries not opening or do I have a vacuum issue? Any help would be greatly appreciated.
Let me shed a little light on what you said in your comments! You said when you punched it! A quadrajet carburator is a vacuum assist carburator, Unlike Holly and edelbrock carburators that have manual linkages operating most everything but the choke plate that you can purchase manual or vacuum assist, The quadrajet is operating any moving parts such as the secondaries with a vacuum signal! And that vacuum signal is not instantly on demand just because you wish you could stomp the loud peddle to the floor and have immediate response! It was designed to be a drive ability carburator, Not a race car carburator! And don't get me wrong! If you have good pieces in an engine and you kinda ease it to the floor giving it time to receive it's vacuum signal your in for a hell of a ride! It's a spread bore model, meaning that the primary circuit is sized for normal driving conditions. But when you get the secondaries to perform with the mind set that you can't just plant your foot to the floor expecting it to react like a top fuel funny car! They have monster size throttle plates that flat get with the program! Even Holly carburators had a spread bore carburator on all the hot cars like 1966 chevelles that had 396 big blocks under the hood! You just got to act like a grown up! Not a teenager that has a badass car but not a bit of commen since to know how to actually make it perform the way the manufacturer made it to work! When I was 25 years younger I started messing around with quadrajets and was lost on a few things! So I purchased a book from a guy named Doug Roe who was employed by general motors in the quadrajet division. That is when I got pretty good at rebuilding and tuning them and I highly recommend that if you want to take the guessing game out of owning a quadrajet you need that book!
Ported vacuum has nothing to do with RPMs. It has to do with how far the throttle blades are open. At idle, there is no vacuum at that port until the throttle is opened more.
First of all thank you for you videos. I have bought a Quadrajet for my 1976 Oldsmobile Cutlass S with a 350 stock engine. The owners before me has put on a Holley 4360 carb for some reason and this is really not a good carb. The quadrajet I bought is a 1976 from a 350 chevy truck. The problem is that it seems to be only one ported vaccum port. Can I use it for both the distributor and EGR or shall I disconnect the EGR? Thanks again. Anders/Sweden
i want to add a edelbrock air cleaner but the vacuum line connects to my stock air cleaner pan connects to it and will shot off when i put the new air cleaner on
#2,like once I go up a hill its starts to bogg and hesitate,cough and burp,,it not the time but usually in when ya go to 3rd gear {automatic}it boggggggs and pisses me right off ,, have to put my hazaeds on till it rectifies itself after about a couple minutes ,, vaccuum,, float ,,sticky or no werky back barrels flapvalve thang ,,,I bought the truck this way 79 scottsdale camper special 350,,,hope to here from ya ,,,thanx for all your vidz and still watching and learning
Great video!! Now tell me what's wrong with my vacum diaphragm on my rochester that doesn't RELEASE and vacum keeping shutt even after engine is hot???
Disconnect the linkage and the vacuum line. Push in the diaphragm. If it fails to spring back out, it's defective. If it springs out, the linkage is probably binding.
yes it is i rebuilt it and it starts good and idles nice choke comes off properly. when i move it and apply the brake it quits. one pump of throttle and it fires right up again. ive un hooked the advace from the vacume port it was on and plugged it and it still quits.
On the port, you claim is ported vacuum for the distributor advance, I'm getting full manifold vacuum here??? At least that's what my gauge is reading when I hook it up there at idle??
Tyler I’m running a 403 in a hot rod I’m building. I took out the pcv system and blocked off the breathers on the valve covers. I put vintage Olds valve covers on top of the original valve covers. Sounds dumb but you can see what I’m talking about if you check out my RUclips channel. The motor is a 307 mock up in most of the videos. Anyway I plan on venting the oil filler neck. Will that be enough or will I have problems. Thanks for all the great videos, I learned a lot from them.
Bro can you do a video of how everything works with it installed on a car, table shots are explanational but i have a divorced choke system and im trying to fab it onto my ramcharger with a eddlebroke intake and i just cannot figure this damn thing out, im not gonna give up cause i was told it is hands down the best for offroading but for the life of me i cannot figure out this choke system
Hi just a started watching 2-3 vidz ,,HELP,,back butterflies valves big barrels} wont open up at all or tiny little bit when I stomped on the gas ,,also the real problem is once i put a load ,or on a hill ,it wants to bogg and hesitate seriously and i loose speed ,, also tried punching the gas makes it worse ,, have to drive my3/4 ton 79 camper special chevy slow to get anywhere ,,its an old truck ,,I know its a huge list but can ya pin piont anything ? learning curves for me man
I had a 67 Impala that originally had no thermostatic valve on the air filter. 68 and later had it so thinking I'd improve the warm up characteristics of my 67 I retrofitted the 68 system and lo and behold much better idle and off idle on a cold motor.
Thank you for your video's, I am having trouble with the front vacum brake, it's new and rebuilt the carb but when the car warms up the front vacum brake never opens up to allow the secondaries to open, rechecked vacum lines for correct ports and I cannot figure it out?
The vacuum choke pulloff must have constant vacuum, if there is vacuum but it doesn't move there's a good chance the internal diaphgram is leaking. Confirm the device is working. The pulloff device should move immediately at startup. Post the carburetor number if you need more info.
at the back top of my quadjet there is a vacum connection that connects to a plate on the intake manifold. Is this also part of the brake boost vacum system. I ask because it goes from rubber hose to steel pipe on the intake manifold and the pipe on mine is loose just wondering how that affects things
@@TylersNeighborhoodGarage Thanks. I bought a hard line and it has a U-turn on the end with a reduced tip to fit into 1/8" rubber. I picture it going straight into the carb body. 1973 K10 by the way...
The real problem started when one of the studs holding the 2GC 2 barrel on burned through. The studs go through the exhaust crossover in the base of the carb and I must have had the wrong grade studs. The quick and dirty fix was to put on a later intake without the carb base crossover but also without the oil fill pipe. That was when the cold driveability problems started in ernest. In hindsight I would have been better off to replace the burnt stud AND use the 68 Thermac system.
Hi Tyler, I have a 1978 Qjet with a vacuum port on the back at the very top. What would this generally be used for? Right now it's plumbed directly to the intake manifold.
+James Jewell That's not a vacuum port. That's the fresh air source for the hot air choke. Search my videos for the one I made a year or so ago explaining hot air chokes
After some issues I was working on, I no longer believe in hooking up a vacuum advance to a ported connection. Run it straight to intake vacuum. Do some research on it. It is, paraphrasing heavily, an emissions band aid. All ported vacuum is. Trans modulators, PVC, brake boosters and vacuum advances should never be on ported vacuum circuits. Just some info.
You have that bass ackwards. Why the hell would you need all of your distributors advance at IDLE, which is where manifold vacuum is which drops off as rpms increase instead of ported where the vacuum advance kicks in like it's supposed too?
Tyler's Forgotten Car Rescue Hey love the videos. But on my 71 olds 350 quadrajet there's a vacuum port centered behind the top back of the carb. Not sure if it stays open to assist air intake but there's already a vent on top like right in front of it practically next to it. Idk if u forgot to address this port or it was a year/make/model exclusive thing. The choke pulloff is already hooked up so its not for that. Maybe for that air cleaner valve? Think i should plug it off? Anyone have any thoughts? Thanks
One of those is the intake for the hot air choke and should have the choke line connected to it. The other, i've never seen before but I think I found a forum post that concerns it. Hopefully it helps. classicoldsmobile.com/forums/442-30/71-w30-auto-vacuum-lines-schematic-117100/
Hey Tyler I have a question for ya and hopefully you can send me in the right direction.. I have a 86 chevy 4x4 van with a new quadrajet on it and when im headed up a hill it wants to bogg out on me and loose power, if i give it gas it just makes it worse, but if i downshift and keep my rpm's high it gets me up the hill but its very gutless... sometimes i can feel it boggin out on flat terrain as well when Im accelerating thru lower rpm's, i can feel the engine tryin to run proper and its gets these short bursts of power and eventually will even out once i hit a higher rpm... i'd love to get this thing running in the proper condition and any leads or idea's are very helpful. Thank you very much for posting all these video's!! you do a great job in explaining things and the camera work is great!
Hey man: Are you positive it isn't misfiring? As I mentioned in a recent video, sometimes other issues mimic carb problems. I would make SURE the base timing is spot on and also rule out misfiring before you come back to the carb/fuel system. The "short bursts of power" doesn't sound like a carb issue.
On my 77 TA there's a thin plastic line coming from the firewall that runs the heater it needs to go to a vacume input on the carb but which one..the thin plastic line also has a check valve on a thin vacume line attached to it.. thanks for any help
So I got a question for you my Rochester 4 bbl vacuum seems to be backwards from yours I have ported vac on the passenger side and manifold vac on the driver side. Why do you think that is? Also when I put a vac gauge on manifold vac the needle bounces around by like 4 or 5 inHg what could cause that? Thanks for all your help and your videos! They are a real help !
Update the needle bouncing around was due to a bad vac gauge. So that problem is solved. But still would like to know why my ported vac is on the opposite side.
I have a '83 Ford Fairmont Futura. It's got the straight six. I'm having trouble with it starting from time to time. I replaced cap, rotor, plug, wires and starter and starter cylinoid. Oh and the fuel filter, air filter and the little filter that sits next to the air filter. I've even given it an oil change. There was a vacuum hole under the carb that I plugged up. But there are three nipples that need hoses attached. I've looked at the diagram under the hood. Need help. It runs great.
Maybe someone can help I bought a rebuilt carb from internet site and my car is idling super high caused car to over heat. I can't get it to kick down.???? First step?
waooo!!! por lo que alcanzó a entender esta muy bien explicado, igual que otros videos donde explica cómo ajustar, lamentablemente en México no hay quien explique asi, ojala hubiera explicación en español, ya que esta muy bien toda esa información, yo tengo una suburban 1990 con carburador rochester cuadrajet pero no se como darle mantenimiento ni ajustarlo, no trabaja bien y sinceramente no la uso mucho porque temo a que se perjudique algo más, saludos y aunque no entienda el idioma me doy una idea por lo que veo. Muchas gracias! !!
Waooo !!! So I came to understand this very well explained, like other videos where it explains how to adjust, unfortunately in Mexico there is no one to explain it, I wish there would be explanation in Spanish, since this is very well all that information, I have a suburban 1990 with Carburetor rochester cuadrajet but I do not know how to give maintenance or adjust it, it does not work well and I honestly do not use it much because I fear that something more is hurt, greetings and although I do not understand the language I give an idea as to what I see. Thank you very much! !!
So there is no vacuum at idle for the egr and the vacuum advance right? And for the canister we are supposed to use a constant vacuum correct me if i am wrong Thanks a lot !
ive got a 85 trans am and half the hook ups and vacuums are all broken or rotted. so it runs like crap. where can i find replacements other wise im just going to rip it out and change out all the 'computerized' stuff like the manifold and distributer.
Well, you know they are there for a reason. Are you trying to clean up the engine bay? I'm not a good person to ask because I leave things mostly stock. A 350 Olds has the bare minimum of vacuum lines as it is. Find a diagram, study it until you understand what's what, then make your changes. You sure it isn't a 307? Those are COVERED with vacuum lines.
Brian Nye Oh. Well in that case, you'll just need the basics. Distributor advance connects to a PORTED, not manifold vacuum source. Other than that, you may have a modulator line to the trans if it's a TH350, metric 200 and 2004R won't have one. You'll have a line for the brakes and one for the climate controls, that stuff is already there. You can use the 307's carb just to get it running, but it's calibrated WAY too lean for a 350.The computer distributor will run it, but the computer calibration is all wrong.We tried that. Once we put the right 350 Qjet, distributor and exhaust manifolds on it, it felt like it picked up 80hp. The carb to get is a 77-79 Olds 350/403 carb.
1985 and later 307's have tiny ports and you never want to use any of that stuff on a 350 or 403. The 1980-84 flat tappet 307 has ports that are about the same size as 350 ports....intake and exhaust, so they'll work ok on a 350. As I said...a 77-80 Oldsmobile 350 or 403 is configured very close to a 307, so that model carb fits perfectly, and the distributor works well, since it is straight mechanical, not computer-controlled. If you aren't sure which version 307 you have, early has 5A heads, later has 7A.
i have the 7a heads, the only thing i plan on using from the 307 is the carb. i have the complete motor rebuilt. i just dont have a carb. so i was hoping to use the q jet from the 307 and delete alot of the vac lines.
Guess what?!? Engines need extra timing advance at idle, therefore the vacuum advance needs manifold vacuum!!! Having said that some early emissions setups have a thermal switch to switch between manifold and ported vacuum. If the engine needs more heat the thermal switch allows ported vacuum which provides no advance at idle, which builds more heat in the engine, when the engine is warm enough the switch allows manifold vacuum to advance the timing at idle for better flame front propagation and not allow the engine to overheat!
You may not see this so many years later but this was a huge help!!!!!!! I’ve been searching forever for someone that cares about what vacuum ports do what!
You have no idea how you just saved me and my ol girl. I wish i had you as a friend. I have been searching forever for something like this.. mine was hooked up allll wrong.
Thank you so much for posting! I have a 86 Chevrolet Camaro and all your tutorials on Quadrajets are so helpful.
Thx for taking the time to post this content.
It popped up when I was researching vac lines on an old motorhome I took apart months ago for a quick fix, and then got sidetracked and forgot what hooked where in the time between...lol
This is 101 auto mechanics. I have two carbs one for my 76 GMC truck restore project and 84 van. I learned more here than I learned in any book I seen so far about vacuum lines.
I recently rebuilt my '89 Olds 307 as a student auto tech project (idiot, I know) and since the c-virus, the project was paused mid-reassembly in the vehicle. Once it got it back home and put everything back in the engine bay, I missed a port on the the carb and it didn't run right. Since it's been months I couldn't remember what went where, even with marked vacuum lines. This explanation helped identify and confirm my carb's setup and now the wagon runs great!
sweet!
You saved my life again. After watching this video i went and rewired the vaccum lines and vala, no more hesitation at idle or accelerating from dead stop. For me the distributor vaccum was not connected to ported vaccum so i fixed that and the back vaccum wire was not connected to the Air cleaner port.
Thanks for the video
That extra port usually has a diaphragm that acts as a brake on the secondary air flaps and makes it open smoothly and sometimes there are two that slow them down when closing like you said to prevent flutter. I had an 850 3 ring primary Venturis. Ford 429CJs used a similar carb but they had a Chevrolet type fuel inlet that went to the side. The BOP carbs usually have straight in the front. The only weakness about the QJet were the well casting plugs needed a thin smear of JBWeld around them and it has to be thin or you can crack the body or throttle plate. If they seep you will notice heat soak. Also when the throttle shafts are worn from having too heavy a spring and you get a vacuum leak, they are done, get another carb. Holley made a good solution, the one piece Autolite style 8011 Spreadbore. They are great carbs , better than the 4165 spread bore. Once the QJet gets a vacuum leak in the shaft they are so lightly made, good luck ever trying to bush it. Ask me how I know.
His seminars are very informative! Worth the time in full!
Thanks Tyler! Even many years later your videos are still helping us Billy Bob's out here in Quadajetland.
THANK YOU THANK YOU THANK YOU, I've been building a 75 eldorado for about 3 years now EVERYTHING is new from the ground up but I just could not figure out the carburetor. In my defense I was never much of a car guy growing up lol but building this car I learned alot and I searched RUclips for months and right when I was about to give up I stumbled upon your page and finally got a great break down. So like I said before THANK YOU THANK YOU THANK YOU
Thanks! Great car too.
First,I want to say your q-jet videos are great.I've enjoyed them very much! One disagreement though. The factory setup for my 79 TA's with Olds 403's is manifold vacuum going straight to the vac advance using the upper right manifold vac port. Also, in my 70's and late 60's factory service manuals, most show manifold vacuum.So, the assumption that ported vacuum is always used for the vac advance is incorrect.My engines run stronger and cooler on manifold vacuum.Thanks again for your vids!
Thanks for taking the time to post this.Official chevy light duty truck manuals dont show this.Sure they have vacuum diagrams but most vehicles with a quadrajet are over 30 years old!Thanks again!I was able to make my 1985 g20 van with esc use a 1980 quadrajet after I disabled the esc computer thanks to your video!
This has helped me a lot, thanks Tyler I have learned a lot about these carbs from videos!
no, that's the fresh air source for the heated choke. The nipple on the carb isn't a vacuum source. It provides filtered air that is then drawn through a metal line to the plate on the intake(which actually has another metal line inside the intake) and then back out through a short line to the hot air choke.
Hey Tyler. I'd like to thank you for taking the time to make the videos, and supply those of us who aren't as knowlegable as you and thanks, while I'm at it for putting it in a manner that common people can understand .carbs have always been a pain in the butt for me. I watched all your videos, a couple of them a few times. but when I got the carb back on the 1976 k20 camper special and turned the key it fired right up and purred like a kitten! I was amazed, I was happy, and thankful to you for taking the time to help the other guy. maybe I can share what I learned from you with someone who is stuck like I was. thanks again for doing what you do
Great video... ty. I have a 1985 Camaro that is giving me a fit. This has helped me find my way some..
@Razastar1971 You can cap off whichever ones you don't need. Whether or not you use vacuum from the carb doesn't affect it's operation in any way unless you leave off a cap and cause a vacuum leak.
Thanks doing my first and last carb. Im learning things only do once. My 77 RV 455 olds. Needs carb redone its the original. When you first look at them they look intimidating. But after watching good vids like yours 10 times im ready to try.
Thank you SO much.I have a 1979 Chevrolet G-20 Van that was built for 80 and apparently has a Quadrajet made by Carter for GMC but has a lot of simularities to a thermoquad as well being made by Carter. I'm having to go back and redo the vacuum system and also make room for other stuff. I have an expansive shelf of different carburetor manuals and shop manuals and none of them hit the nail on the head like this video. I had nothing to go by but feel and this nailed every port on the front i had questions about (specifically for the EGR and Charcoal vent) I'll have to take pictures or video on this thing cause its a frankenstein carb in design. THANKS! :D -Foxi D'elegance
At about the 10:35 mark of this video, we always called that vacuum pod the choke pull off, if it's not working properly, the engine will not run properly, because it's choking itself to death using more gas, it may even cause your engine to have a miss, you'll also have excessive black smoot around the end of your tailpipe, I can't even begin saying how many choke pull-offs I've had to replace during my mechanic career. The front vacuum pod is what engages the choke, and the rear vacuum pod disengages the choke, they're designed to work together, along with the divorce manifold heater coil. If your secondaries doesn't open when you floor it going down the road, there's a very good chance your choke pull off or something within the choke setup is the problem. I personally think that the Rochester Quadrajet 4-bbl 750/800 cfm carburetors are one of the best designed carburetors ever built. I've heard so many people talk bad about the Quadrajet, but like anything else, you gotta be smarter than the equipment you're operating. I'm a retired mechanic, but even during my working days, it didn't matter if I was working at a GM dealership or independent auto repair shop, very few mechanics actually knew how to properly rebuild and or tune a Quadrajet 4-bbl carburetor, yet they're so simple to understand how they're designed to function properly. I'd take a Quadrajet carburetor over a Holley, Edelbrock, or Carter anyday for a stock engine up to a moderately cammed and or modified street engine that'll turn 6500 rpms, it mostly depends on what camshaft will be used in the car and or engine, Holley would be my second choice.
Some Buick Olds Cadillac QJs use both choke pulloffs in a staged setup where the front one opens the choke a little right away. Then the rear pulloff opens it more a little later due to the restriction built into it's vacuum fitting. This has the effect of enabling earlier choke opening to cut down on cold engine emissions. That little restriction also has a bleed in it to let the pulloff modulate the choke spring tension. Early QJs had only a single front pulloff made of plastic.
Thank you for posting this and thanks to you tube community for digging it up.
Well, that's all they ever have. It won't hurt anything to share the one vacuum source, but keep in mind that GM's of that vintage including your Olds ran the ported vacuum signal through thermostatic vacuum valves that would not permit egr or distributor advance until a certain coolant temp was reached.
It was purely for emissions, but if you wish to have it like it originally was, you can google 1976 Olds vacuum diagrams and search the "images"
Great video. I have a Q-jet that has a threaded hole where you have a nipple connection that you said was for the distributor vacuum advance. It's on the front that is to the right of the fuel input and half way up the carburetor. My vacuum advance was connected to the small one on the front bottom right. What do I do with this threaded hole to make the connection to my distributor? What type of threaded connection do I use? I also have the threaded hole on the back for the power brakes. I have manual brakes but I want to convert to power. Where do you get the fittings for this as well? Thanks.
H WhoSaidTyler,
Is there any way to remove all these vacuum hoses? i remember on edelbrock i only had the vacuum from the dristributor and the fuel lines. Rest were tapped.
Thanks
Thank you great video. Doing a father son project on a 83 blazer and these vacuum lines have my head spinning.
What’s the little tube in the back of the carb for?
Tyler, my-quadrajet-go-to-guy, I've got something that's got me perplexed on my truck. If it helps; it's an 81 GMC c3500 2wd 350/th400/4.56:1. The carb is a 17059216....you know the kind 😁
As far as I can tell everything is dialed in damn well. The idle mixture is nice, idle is 650-700 in park with vac disconnected. It drives 99% perfect. I've got a little problem in my timing. I've read the stock vac advance pulls too much on these and that seems like what is happening BUT I think the source might be the carb.
***Ok here's the question: should there be ZERO vacuum at the ported port at idle? As you say in the vid from **3:45** to about **5:45**? *** I have a pretty strong vacuum signal there. I haven't measured it.
Base timing is 8 degrees. When I connect to that port it rises to 20 degrees. And, if I go to strait manifold vacuum it'll rise to 26 degrees. All these numbers are at idle. If I back the idle speed screw out any more or fiddle with timing it will want to die out.
I have a 1983 chevy g 30 van with a small block 350 and quadrajet 4bbl carb .
I have a question ;
Why does my timed vacume port have constant manifold vacume instead of timed ?
I was not aware that the quadrajet was manufactured with the carb having no timed vac port snd the tyipical timed vacume port having manifold vac
Could the port on the carb on the back side be used for the th400 vaccum line??? Also where else can that vaccum be take from? Thanks for the video.....was looking for some explanation for a Rochester. Very informative!!
What about the vaccuum line at the rear?? Is it for the brake's power booster??
Mine has been cut on an E4MC from '81.
How do I extract the crimped line for then to plug a new metal pipe??
I want to reconnect that line again into the power booster for the brakes.
Hello Tyler, came across your video great info. I put a newer carb (1985) on my old motor and find i have vacuum all the time on the what used to be ported vacuum port. I'm assuming the car it came off had some emissions, TVS, vacuum delay or check valve on it. How do I correct this? any help will be much appreciated
a while back ago, i was fixing on my cutlass. and i broke the line that screwed into that big circle thats right in the front of the carburetor. can you tell me what that big circle screw in is for and what line that is? thanks brotha.
Your VAC sensor (inverse readings of MAP) will tap into where that secondary choke pull off line is in CCC models.
I would absolutely appreciate it if you could do this with a late 80s Rochester Quadrajet with computer controls
I subscribed thank you
Tyler, can you please help me? I have a quadrajet and it's on a 455 toronado from 1974. I'm going to utilize your fast idle adjustment because I feel mine is high but the problem that I'm having now is from an idle once the vehicle is warmed if you barely depressed the gas pedal, it bogs down and sometimes stalls if you hold it but if you push it further it will work its way through the bog and the RPMs will raise fine. What is causing this initial bog? I've watched your videos but can't seem to find one that covers that early bogging off idle. There are plenty of videos about Holly carbs doing that, but I can't find any on quadrajet. You're wonderful!
Hello,I have wondered if you block off a vacuum port or two does it increase the internal vacuum pressure?If so what problems are there tht mite occur
thanks to you ive corrected some errors, i only have 1 port that vaccum exists at idle and it was hooked to the distrubutor valve 0_o now i have everthing that looks like a egr hooked on a ported valve. the heater unit i hooked to the idle vaccum port. at least i think its the heater unit bcuz it used to switch the interior vents faster when i was on the throttle, now it switches fast all the time. my bouncy idle was also reduced as well, i think it was making it hard to set the mixture. my brake booster has its own port on the manifold so im good there. my pcv was hooked to the factory filter case but it was before the filter and my edlebrock air cleaner has the pcv hole AFTER the filter so i left it off with a tiny pcv filter on it. its temporary as im trying to rig something to mount it on and before the filter. thanks for the help
I have no laws concerning emmision testing and I just want to get the car started after sitting 20 yrs. What do i need to start it. I know i need fuel but what else.
Thanks for posting! You've answered several questions I had!!
mike cole your videos have helped understand adjustments and what to look for so thanks
everyone i know with a quadrajet including myself runs manifold vacuum for distributor advance. everyone around here believes that to be the best way to do it. is there any advantage to port vacuum advance on a k20 i daily drive and tow with with a stock 350ci and sm465?
Thank you so much for the information. I don't understand very much english but please correct me if I'm wrong. Distribuitor advance is conected at the ported vacuom in driver side fron front of the carb. I miss were to conect the shock line usually goes into the intake, my intake don't has that hole and I'd like to know if is posible conect it at any other vacuom.
Sir I have watched all the videos that you have posted about the Quadrajets. I am a Novice Mechanic. I am working on a 86 Chevy Monte Carlo. On the Quadrajet that I have I am referring to the Vacuum breaker. Even after the engine reachs operating temp. The Vacuum breaker is not releasing Vacuum to allow the Secondaries to open at all. Do you have some helpful advice for me so I may fix this problem?
The vacuum break stays engaged until the vacuum signal goes away, which happens at full throttle. If you hook a vacuum gauge to your engine and position it where you can watch it as you drive, you'll see that normally there is about 15" of vacuum at idle and light throttle. The heavier the throttle application, the less vacuum available.
So, that vacuum break is working. You just can't see it because it's hard to rev the engine that hard standing there to get to zero vacuum.
I suspect there may be something else preventing the secondaries from operating, but not the vacuum break.
I stumbled on to your videos last night and watched every one I could. I have learned more about my carb than any books, websites or videos that I have seen in the past 12 years. I've already put some of your teaching to use. (I was one of the guys that had those back butterflies so loose they almost fell open) One question: Everytime I step on the gas my car hesitates for just a second, like a dead spot. what causes that? My carb was "pro" rebuilt a couple years ago and has always done it.
I posted info on your video. Let me know if you need more help. I forgot to mention that if there's a choke pull-off on your carb, and it looked like there was, it connects to a MANIFOLD vacuum source.
So what would you do with the charcoal vacuum connection on the carb if you're not running a charcoal canister? Do you just block it off? Does it need to be vacuumed? Rat rod application...
Leave it open to the atmosphere. Otherwise it could cause hard starting from vapors having nowhere to go except inside the air cleaner. If you want to be fancy you could glue a small piece of microphone foam over the end to keep the dust out.
Thanks. I'm gonna put some kind of breather filter on it. Maybe even just a fuel filter open on one end.
Now I have to figure out a kick down system as the carb came off a car with a th400 and my set-up is a 700r4. Oddly enough, the carb has a strange "screw on" linkage plate attachment on the end of the primary shaft. So I'm gonna take one with the th400 tv cable hook up, match it with a set of holes like the linkage plate that's on it now and screw the new one with the tv link on like the one that's on there now... Otherwise I'll have to change the entire primary shaft. Those butterfly screws are a bitch!
Ive watched all your videos on the Rochester (several times). Can you do a video on how the linkages are connected behind the choke? My secondaries arent opening correctly and I believe the linkage behind the choke isnt assembled correctly and therfore the "stop lever" on the secondaries isnt connected/operating correctly.
Also, the air/fuel mixture screw on the choke side of the carb doesnt have any effect on the idling when I turn it in either direction. The mixture screw on the drivers side ( or closest to the idle screw ) works fine and theres an obvious idle change when I turn the screw. Whats up with the choke side mixture screw not changing the idle when turned fully closed or fully open?
Thanks!!!
Sure. Could you provide me the carb# stamped vertically on a rib on the driver-side of the carb?
As far as the mixture screw not reacting on one side...I bet you know the answer but don't KNOW you know it...so I'll test you: if one side of a faucet works and the other doesn't...or...if a vent on one side of the dash blows air but the other side doesn't, what would you suspect to be the reason? Same principle in all cases.
WhoSaidTyler
Yep! I cleaned the idle mixture screw port and its working properly now. Unfortunetly I have an oil leak from the head gasket so I need to get that fixed this weekend. Someone scratched out the serial number so im stuck with what Ive got. Its an electric choke carb which was all rebuilt and very clean.
When I removed the carb the lower secondaries open just fine. I noticed the. "stop lever/ stop tab" is just dangling in place though. The choke linkage does however touch the stop lever when on full throttle and releases the stop lever so the secondaries open. After releasing the full throttle the stop tab doesnt have any tension on it and can move freely.
I had a question I have a 74 Buick Electra with a 455. And after doing a top end rebuild I forgot where all the vacuum hoses go. And for the life of me I can't find any diagrams for it. Do you by chance know how they are routed.
Hey Tyler. You are awesome. Thank you for your videos. I have a 350, with a Rochester Quad on my boat. Recently I had a lot of work done to it. I went out the other day and it started right up, motored great at idle and low RPM. When I went to punch the throttle, I had half the power I should have. It felt fuel starved. Now I am confused. Are the secondaries not opening or do I have a vacuum issue?
Any help would be greatly appreciated.
Let me shed a little light on what you said in your comments! You said when you punched it! A quadrajet carburator is a vacuum assist carburator, Unlike Holly and edelbrock carburators that have manual linkages operating most everything but the choke plate that you can purchase manual or vacuum assist, The quadrajet is operating any moving parts such as the secondaries with a vacuum signal! And that vacuum signal is not instantly on demand just because you wish you could stomp the loud peddle to the floor and have immediate response! It was designed to be a drive ability carburator, Not a race car carburator! And don't get me wrong! If you have good pieces in an engine and you kinda ease it to the floor giving it time to receive it's vacuum signal your in for a hell of a ride! It's a spread bore model, meaning that the primary circuit is sized for normal driving conditions. But when you get the secondaries to perform with the mind set that you can't just plant your foot to the floor expecting it to react like a top fuel funny car! They have monster size throttle plates that flat get with the program! Even Holly carburators had a spread bore carburator on all the hot cars like 1966 chevelles that had 396 big blocks under the hood! You just got to act like a grown up! Not a teenager that has a badass car but not a bit of commen since to know how to actually make it perform the way the manufacturer made it to work! When I was 25 years younger I started messing around with quadrajets and was lost on a few things! So I purchased a book from a guy named Doug Roe who was employed by general motors in the quadrajet division. That is when I got pretty good at rebuilding and tuning them and I highly recommend that if you want to take the guessing game out of owning a quadrajet you need that book!
Ported vacuum has nothing to do with RPMs. It has to do with how far the throttle blades are open. At idle, there is no vacuum at that port until the throttle is opened more.
First of all thank you for you videos. I have bought a Quadrajet for my 1976 Oldsmobile Cutlass S with a 350 stock engine. The owners before me has put on a Holley 4360 carb for some reason and this is really not a good carb. The quadrajet I bought is a 1976 from a 350 chevy truck. The problem is that it seems to be only one ported vaccum port. Can I use it for both the distributor and EGR or shall I disconnect the EGR? Thanks again. Anders/Sweden
i want to add a edelbrock air cleaner but the vacuum line connects to my stock air cleaner pan connects to it and will shot off when i put the new air cleaner on
I have a quarter jet off and 81 Camaro that loads up after starting. The choke butterfly does not seem to open enough to allow more air. Any ideas?
#2,like once I go up a hill its starts to bogg and hesitate,cough and burp,,it not the time but usually in when ya go to 3rd gear {automatic}it boggggggs and pisses me right off ,, have to put my hazaeds on till it rectifies itself after about a couple minutes ,, vaccuum,, float ,,sticky or no werky back barrels flapvalve thang ,,,I bought the truck this way 79 scottsdale camper special 350,,,hope to here from ya ,,,thanx for all your vidz and still watching and learning
Great video!! Now tell me what's wrong with my vacum diaphragm on my rochester that doesn't RELEASE and vacum keeping shutt even after engine is hot???
Disconnect the linkage and the vacuum line. Push in the diaphragm. If it fails to spring back out, it's defective. If it springs out, the linkage is probably binding.
yes it is i rebuilt it and it starts good and idles nice choke comes off properly. when i move it and apply the brake it quits. one pump of throttle and it fires right up again. ive un hooked the advace from the vacume port it was on and plugged it and it still quits.
Thanks a lot of real good help and big explanation
On the port, you claim is ported vacuum for the distributor advance, I'm getting full manifold vacuum here??? At least that's what my gauge is reading when I hook it up there at idle??
@WhoSaidTyler thanks for the info.
Like i just cannot figure out how to mount the thermostat on the intake and im pretty sure i screwed up my vacuum lines
Tyler I’m running a 403 in a hot rod I’m building. I took out the pcv system and blocked off the breathers on the valve covers. I put vintage Olds valve covers on top of the original valve covers. Sounds dumb but you can see what I’m talking about if you check out my RUclips channel. The motor is a 307 mock up in most of the videos. Anyway I plan on venting the oil filler neck. Will that be enough or will I have problems. Thanks for all the great videos, I learned a lot from them.
Can you do a rundown for a dualjet......I have several ports unplugged
Another great video. I'll be an expert after watching your videos. Ok not really but a little more informed at least.
+A. Dubs Many Endeavors Thank you for the kind words.
can you just plug the air cleaner vacuum tube cause i want to add a edelbrock air cleaner and take off my old metal pan air cleaner on my 305
I hate how my Qjet is always plotting against me...
Springfieldm14 308winchester
Dial it in.
Trust me. Even on a stock engine
.. you'll grow to love it.
Ha, you to...!!?? I’m struggling with mine currently.
Bro can you do a video of how everything works with it installed on a car, table shots are explanational but i have a divorced choke system and im trying to fab it onto my ramcharger with a eddlebroke intake and i just cannot figure this damn thing out, im not gonna give up cause i was told it is hands down the best for offroading but for the life of me i cannot figure out this choke system
Hi just a started watching 2-3 vidz ,,HELP,,back butterflies valves big barrels} wont open up at all or tiny little bit when I stomped on the gas ,,also the real problem is once i put a load ,or on a hill ,it wants to bogg and hesitate seriously and i loose speed ,, also tried punching the gas makes it worse ,, have to drive my3/4 ton 79 camper special chevy slow to get anywhere ,,its an old truck ,,I know its a huge list but can ya pin piont anything ? learning curves for me man
I had a 67 Impala that originally had no thermostatic valve on the air filter. 68 and later had it so thinking I'd improve the warm up characteristics of my 67 I retrofitted the 68 system and lo and behold much better idle and off idle on a cold motor.
appreciate the video. Gonna be alot of the younger generation youtubing this kind of stuff when they get their naturally aspirated motors going lol.
Alabama. Thanks man!
Very helpful, although I wish the picture quality was better.
Thank you for your video's, I am having trouble with the front vacum brake, it's new and rebuilt the carb but when the car warms up the front vacum brake never opens up to allow the secondaries to open, rechecked vacum lines for correct ports and I cannot figure it out?
The vacuum choke pulloff must have constant vacuum, if there is vacuum but it doesn't move there's a good chance the internal diaphgram is leaking. Confirm the device is working. The pulloff device should move immediately at startup. Post the carburetor number if you need more info.
at the back top of my quadjet there is a vacum connection that connects to a plate on the intake manifold. Is this also part of the brake boost vacum system. I ask because it goes from rubber hose to steel pipe on the intake manifold and the pipe on mine is loose just wondering how that affects things
Thank you, this was a huge help. :)
Good info. Where does the modulator hook up?
To the vacuum tree on the intake behind the carb, or at least to a MANIFOLD vacuum source.
@@TylersNeighborhoodGarage Thanks. I bought a hard line and it has a U-turn on the end with a reduced tip to fit into 1/8" rubber. I picture it going straight into the carb body. 1973 K10 by the way...
The real problem started when one of the studs holding the 2GC 2 barrel on burned through. The studs go through the exhaust crossover in the base of the carb and I must have had the wrong grade studs. The quick and dirty fix was to put on a later intake without the carb base crossover but also without the oil fill pipe. That was when the cold driveability problems started in ernest. In hindsight I would have been better off to replace the burnt stud AND use the 68 Thermac system.
Thanks, working with a quadra on a factory installed 350 Olds in a 1981 Eldorado, because the original diesel sucked. Unique setup indeed
Very helpful, thanks!
Hi Tyler, I have a 1978 Qjet with a vacuum port on the back at the very top. What would this generally be used for? Right now it's plumbed directly to the intake manifold.
+James Jewell That's not a vacuum port. That's the fresh air source for the hot air choke. Search my videos for the one I made a year or so ago explaining hot air chokes
The port at 8:34 on the left is also a ported vacuum. I have the vacuum advance to distributor connected to it.
After some issues I was working on, I no longer believe in hooking up a vacuum advance to a ported connection. Run it straight to intake vacuum. Do some research on it. It is, paraphrasing heavily, an emissions band aid. All ported vacuum is. Trans modulators, PVC, brake boosters and vacuum advances should never be on ported vacuum circuits. Just some info.
You have that bass ackwards. Why the hell would you need all of your distributors advance at IDLE, which is where manifold vacuum is which drops off as rpms increase instead of ported where the vacuum advance kicks in like it's supposed too?
Never say "never". Some engines run better with ported vacuum advance, while others like manifold vacuum.
tremendously
helpful
@TheMaxx1127 The modulator valve always requires manifold vacuum. Thanks for watching.
Tyler's Forgotten Car Rescue
Hey love the videos. But on my 71 olds 350 quadrajet there's a vacuum port centered behind the top back of the carb. Not sure if it stays open to assist air intake but there's already a vent on top like right in front of it practically next to it. Idk if u forgot to address this port or it was a year/make/model exclusive thing. The choke pulloff is already hooked up so its not for that. Maybe for that air cleaner valve? Think i should plug it off? Anyone have any thoughts? Thanks
One of those is the intake for the hot air choke and should have the choke line connected to it. The other, i've never seen before but I think I found a forum post that concerns it. Hopefully it helps.
classicoldsmobile.com/forums/442-30/71-w30-auto-vacuum-lines-schematic-117100/
can i keep a vaccuum tester on any of these ports?
Yes. Cars used to have vacuum gauges installed inside by the factory.
Hey Tyler I have a question for ya and hopefully you can send me in the right direction.. I have a 86 chevy 4x4 van with a new quadrajet on it and when im headed up a hill it wants to bogg out on me and loose power, if i give it gas it just makes it worse, but if i downshift and keep my rpm's high it gets me up the hill but its very gutless... sometimes i can feel it boggin out on flat terrain as well when Im accelerating thru lower rpm's, i can feel the engine tryin to run proper and its gets these short bursts of power and eventually will even out once i hit a higher rpm... i'd love to get this thing running in the proper condition and any leads or idea's are very helpful.
Thank you very much for posting all these video's!! you do a great job in explaining things and the camera work is great!
Hey man:
Are you positive it isn't misfiring? As I mentioned in a recent video, sometimes other issues mimic carb problems. I would make SURE the base timing is spot on and also rule out misfiring before you come back to the carb/fuel system. The "short bursts of power" doesn't sound like a carb issue.
On my 77 TA there's a thin plastic line coming from the firewall that runs the heater it needs to go to a vacume input on the carb but which one..the thin plastic line also has a check valve on a thin vacume line attached to it..
thanks for any help
Bruce Hamilton
So I got a question for you my Rochester 4 bbl vacuum seems to be backwards from yours I have ported vac on the passenger side and manifold vac on the driver side. Why do you think that is? Also when I put a vac gauge on manifold vac the needle bounces around by like 4 or 5 inHg what could cause that? Thanks for all your help and your videos! They are a real help !
Update the needle bouncing around was due to a bad vac gauge. So that problem is solved. But still would like to know why my ported vac is on the opposite side.
I have a '83 Ford Fairmont Futura. It's got the straight six. I'm having trouble with it starting from time to time. I replaced cap, rotor, plug, wires and starter and starter cylinoid. Oh and the fuel filter, air filter and the little filter that sits next to the air filter. I've even given it an oil change. There was a vacuum hole under the carb that I plugged up. But there are three nipples that need hoses attached. I've looked at the diagram under the hood. Need help. It runs great.
Fuel pressure gauge install 350 chevy.
Maybe someone can help I bought a rebuilt carb from internet site and my car is idling super high caused car to over heat. I can't get it to kick down.????
First step?
I'm switching my carburetor and the vacuum hose hole is closed on the one I baught can anyone tell me where else it can be hooked up
waooo!!! por lo que alcanzó a entender esta muy bien explicado, igual que otros videos donde explica cómo ajustar, lamentablemente en México no hay quien explique asi, ojala hubiera explicación en español, ya que esta muy bien toda esa información, yo tengo una suburban 1990 con carburador rochester cuadrajet pero no se como darle mantenimiento ni ajustarlo, no trabaja bien y sinceramente no la uso mucho porque temo a que se perjudique algo más, saludos y aunque no entienda el idioma me doy una idea por lo que veo.
Muchas gracias! !!
Waooo !!! So I came to understand this very well explained, like other videos where it explains how to adjust, unfortunately in Mexico there is no one to explain it, I wish there would be explanation in Spanish, since this is very well all that information, I have a suburban 1990 with Carburetor rochester cuadrajet but I do not know how to give maintenance or adjust it, it does not work well and I honestly do not use it much because I fear that something more is hurt, greetings and although I do not understand the language I give an idea as to what I see.
Thank you very much! !!
I am having no vacuum suction in any of my ports, why would this be?
check for an obstruction
So there is no vacuum at idle for the egr and the vacuum advance right?
And for the canister we are supposed to use a constant vacuum correct me if i am wrong
Thanks a lot !
My email is pcfastncraft@hotmail.com
George Peters
M
ive got a 85 trans am and half the hook ups and vacuums are all broken or rotted. so it runs like crap. where can i find replacements other wise im just going to rip it out and change out all the 'computerized' stuff like the manifold and distributer.
It's just rubber line that you can buy at a parts store. As far as what's broken, you can find that stuff in the junkyard easily.
Brilliant explaination, Top Man
how many of the vacumme lines can i delete from an olds 350?
Well, you know they are there for a reason. Are you trying to clean up the engine bay? I'm not a good person to ask because I leave things mostly stock. A 350 Olds has the bare minimum of vacuum lines as it is. Find a diagram, study it until you understand what's what, then make your changes. You sure it isn't a 307? Those are COVERED with vacuum lines.
Im pulling out a 307 that threw a rod and i built a rocket 350. Im hoping to use the 307s carb though and clean up the engine bay
Brian Nye Oh. Well in that case, you'll just need the basics. Distributor advance connects to a PORTED, not manifold vacuum source. Other than that, you may have a modulator line to the trans if it's a TH350, metric 200 and 2004R won't have one. You'll have a line for the brakes and one for the climate controls, that stuff is already there.
You can use the 307's carb just to get it running, but it's calibrated WAY too lean for a 350.The computer distributor will run it, but the computer calibration is all wrong.We tried that. Once we put the right 350 Qjet, distributor and exhaust manifolds on it, it felt like it picked up 80hp. The carb to get is a 77-79 Olds 350/403 carb.
1985 and later 307's have tiny ports and you never want to use any of that stuff on a 350 or 403. The 1980-84 flat tappet 307 has ports that are about the same size as 350 ports....intake and exhaust, so they'll work ok on a 350. As I said...a 77-80 Oldsmobile 350 or 403 is configured very close to a 307, so that model carb fits perfectly, and the distributor works well, since it is straight mechanical, not computer-controlled.
If you aren't sure which version 307 you have, early has 5A heads, later has 7A.
i have the 7a heads, the only thing i plan on using from the 307 is the carb. i have the complete motor rebuilt. i just dont have a carb. so i was hoping to use the q jet from the 307 and delete alot of the vac lines.
Guess what?!? Engines need extra timing advance at idle, therefore the vacuum advance needs manifold vacuum!!! Having said that some early emissions setups have a thermal switch to switch between manifold and ported vacuum. If the engine needs more heat the thermal switch allows ported vacuum which provides no advance at idle, which builds more heat in the engine, when the engine is warm enough the switch allows manifold vacuum to advance the timing at idle for better flame front propagation and not allow the engine to overheat!
Some ideas GM had WERE good ones!
Thanks from the D 40 years and still get mixed up