GM Quadrajet Rebuild Tips

[@stevesulak9487]

The roar when those secondaries open can't be beat. It's a great carb and very mechanic-friendly. Great video.

[@454Burban]

Agreed. Gotta love the roar of wide-open secondaries!

[@dirtyburd71]

I built one for my v8 mazda truck. Works great! Doing an EFI to carb swap on my '88 LTD wagon and will be building another Qjet for it. I have a four hole spread bore to square bore adapter to make it all work.

[@mark_osborne]

Nice - Bet that's the only Mazda in the entire country with a Q-Jet !!!

[@mediumjumbo7484]

Great old carbs when they are workin good. My fave was the heatriser choke model. Tried other carbs back in the day, but went back to the Qjet for its reliability 👍🇺🇸👍

[@mark_osborne]

yes yes, heat riser choke models, like the Olds version, worked amazingly well

[@steplock1974]

Man know i have to take mine apart and check a few things, i was going to install it on today. Thanks for saving me!

[@lucasblake7224]

Great Video, thank you I have a q jet on my 1970 Pontiac Lemans it run smooth but ITs burning so rich. The file system was completely rebuilt except the carb.

[@mark_osborne]

only when you get into the secondaries ?

[@shawnmartins169]

Thank you so much i Nearly gave up on my quadrogen I've rebuilt it twice air mixture idle screws do nothing I have serious vacuum leaks and now I'm going to go out there and try to rebuild it for the 3rd time after listening to the information that you have shared I feel pretty confident I have a few symptoms that need attention attention I blocked off a vacuum line and I didn't replace those seals That you showed for the joke my choke doesn't mean vacuum line coming off of it as well thank you again I will give it a try and keep you up-to-date

[@shawnmartins169]

So I have filed down the top half of that carburetor man it was seriously warped they worked so badly that I feel that I filed it down the best I could and tried to keep it as level and flat but it still has an arch put it back together what a world of a difference no more white smoke no more overfueling thank you the knowledge that you have sir thank you so much for sharing it with us younger folks Because once that knowledge is gone and it's gone thank you I will keep it for generations to come and I will teach my sons long live Rochester quadro jet carburette

[@flbartlett]

Great video. I"m in the process of putting right a 77 El Camino. Picked up a Quadrajet that the fella said came off of an 83 Chevy Truck. Getting my KZbin education in preparation of rebuilding the unit. Thanks for passing on the knowledge.

[@gpitt1960]

Great points on rebuilding.

[@joeymitsurax5153]

Love your channel!! Keep up the content

[@mark_osborne]

Thank you so much

[@vicburt6001]

Thank you! I went through an auto technology program and we only discussed the basics.

[@mark_osborne]

Thanks for watching !

[@stevefarmer6607]

Thanks for the tips. I haven’t messed with one of these sense 1990 on a 84 cutlass. I told my wife that nowadays there’s KZbin, so I could get a refresher. But I was surprised when I seen your tips. Thanx again man. I bought a 1989 Chris Craft Amerosport with a 5.7 Volvo Penta (aka Chevy 350) and am finding myself going through just about everything except the inside of the block, so far I hope. I’ve redone the cooling system from the router to the tooter except for the intake through the block, I’m going to try a new marine flush for that. Now I’m going through the fuel system from the tank to the carb. I’ve flushed 40 gallons of 3 year old gas from the tank the tank and fuel line to the filter, change to a new canister filter water separator, new fuel line to a new mechanical fuel pump, and now I see the carb has a small fuel leak, but most of all I feel it’s leaking lots of air too. I like the idea of the fuel economy option you pointed out. On a floating camper, speed at take off shouldn’t be that necessary. I was shocked to see the 4 barrel carb when I bought the old boat. But better fuel efficiency would be great on long trips down to the Gulf running about 3k rpm. Great vids. You have a new subscriber.

[@mark_osborne]

Thanks Steve ! and good luck with your restoration :-)

[@johnupton8389]

Thanx for the tips. Has been a long time since I have rebuilt one. Im working on a YJ wrangler I put a SBC in. I thought a quad. was a good choice for whAt I'm after. Keep videos coming buddy.

[@chuckeecheese162]

Excellent video.

[@christopherenglish8863]

Great Video! Going to dig into a rebuild of mine on 1968 Cadillac soon.

[@mark_osborne]

Nice !.... and thanks

[@tabbott429]

thanks i learned some good stuff. I had one rebuilt by a local guy and now that its on the car im struggling to get the idle mixture screws to have any effect at all. Ive advanced the timing and i can still close the mixture screws all the way and the car wont stall. Im running a 1 inch spacer with 4 holes since my linkage wont clear the intake manifold. I finally got the idle screw to make an audibly noticable sound upon opening them but engine rpm doesnt change, im not sure what else could be leaking air. the only vacuum port im using is the ported advance for the distributor and pcv valve. its a 366 tall deck chevy motor with a car intake and spacers. the gaskets between the carb and spacer and spacer and intake are pretty thick.

[@davidbowers6005]

I've got the same problem. Haven't found the vacuum leak yet.

[@11bayrat]

Thanks for sharing.I just rebuilt my 2nd. one.really helpfull videos

[@mark_osborne]

Thanks !

[@tedsmith5678]

I want to thank you for your pointers i appreciated the knowledge that you shared and wanted to know if you know of a good diagram of choke linkage I took pic before tearing down but still having trouble with last 2-3 items of assembly that didn't quite capture in the pics I took

[@mark_osborne]

see if this helps at all www.google.com/imgres?imgurl=https%3A%2F%2Fwww.carburetor-parts.com%2Fassets%2Fimages%2Fquadrajet-choke-intragal.JPG&imgrefurl=https%3A%2F%2Fwww.carburetor-blog.com%2Fknowledge-base%2Fquadrajet-choke%2F&tbnid=yv29QRK3oC3EJM&vet=12ahUKEwi24IuT9Zv5AhVRnGoFHUQIBNcQMygCegUIARCFAw..i&docid=W4_MVfXbIq5BrM&w=683&h=475&q=quadrajet%20choke%20assembly&ved=2ahUKEwi24IuT9Zv5AhVRnGoFHUQIBNcQMygCegUIARCFAw

[@MIketucky350]

all the carbs Ive had. Holley/edelbrock/carter. the qjet was always my favorite. It ran the best. Plus stick one with a overdrive trans and they get killer mileage.

[@mark_osborne]

They DO ! The get as good or better than the first throttle bodies

[@elibatman8474]

Awesome thank you for sharing some knowledge

[@mark_osborne]

Thanks for dropping by the channel !

[@PEDDALIT]

Great video! I’m rebuilding the Quadrajet on my 74 corvette right now. This is a huge help. I’m not sure how the little spring that holds the metering rods goes on, it came off while working on it. I could use help with that. Thanks again for your video! Jerry

[@mark_osborne]

It drops down in the hole the metering rod plunger fits into. It pushes the metering rods up and intake vacuum pulls them down.

[@markpelley]

I have my quad working pretty good but I can’t tell if the secondaries are working. The top air vents won’t move when high reeving. I have the tension set to very light. The secondary shaft will rotate with the engine off and throttle open very far but will not rotate at all when high reeving. I also removed the secondary lock out, still no movement.

[@mark_osborne]

The choke pull-off will keep that top air door slammed shut until the vacuum has a chance to bleed off. Free revving it in "park" doesn't always give it enough time to bleed off the vacuum. Try un-plugging the vacuum line to the primary (right front of the carb) choke pull-off and do the test again. Also, you can visually see the secondary shaft move (open) by looking at the passenger side of the carb. There is a green cross-pin going through the shaft. The lockout thinggy prevents the shaft from opening when it's cold by engaging that cross-pin. It should become very obvious what's going on once you study it a bit.

[@markpelley]

@@mark_osborne Thanks for replying, Mark! Little more background. I have a 1979 Carter Quadrajet and the Vacuum break is at the back of the carburetor. I actually removed it and plugged the vacuum line that is connected to the back of the carb. With the secondary lock mechanism removed, the vacuum break removed, air door tension adjusted to very light, I still don't see the air doors or secondary shaft move at a full throttle rev with the engine running. Funny thing, with the engine not running, I can see the secondary shaft rotate open when i pull back on the throttle. Confusing!

[@mark_osborne]

@@markpelley That is a first for me !

[@joseantoniomendezhumero9428]

I hope you still remember me. I am the guy who told you about a fire in my Corvette C3. After rebuilding we put in place a rebuilt quadrajet, also a new distributor and our problem now is that the idle is not good, about 700 rpm but hesitant. Something that have us flabergasted is that wathever you do to the idle idle screws is irrelevant because there is no change. We don't know what to do and where to start. Other things the advance of the distributor is right. Besides the engine pick up is just perefect and rew up happily. We need your help at this point. Thank you in advance. Jose

[@mark_osborne]

If there is no change when you bottom out the idle screws then there is either a blockage in the idle circuit or the top of the carb is warped to the point where it's not compressing the gasket in the middle of the carb. The idle circuit travels up into the top section of the carb, then back down. Take the top off and lay a flat edge across it. Also, once the top is off, you can take an air gun and blow down into the idle circuits if you know what you're looking at. In the body of the carb (with the top removed) you'll see 2 brass restrictors in the idle circuit. They limit the flow of fuel so that once your idle mixture screws are out past about 3 turns it makes no difference. If I have a car that I can't get rich enough at an idle, I drill those restrictors out a bit.

[@wattan7parrast]

Very helpful tips brother. Thank you I broke off 9 screws from the butterfly assembly. I tapped and drilled them out. Question 1: I go a size higher on the screws? Question 2: should I use treadlocker?

[@mark_osborne]

Sorry I've been out of town. What I have done in the past is use tiny machine bolts and nuts with threadlocker, that way you don't have to drill the holes larger

[@aldonstever8041]

I have to agree with you on the best carb made. People would say there going to throw them away, my reply was throw it my way. My question is I found what looks like a quad in every way except it's a 2 barrel, theres no secondary just the empty holes but the top where the secondary would be has not been cast open its smooth the numbers are 170551710045, fuel intake is like the ones on a oldsmobile straight out the front of the carb. What is it? I loved watching your video to forgot a few things you reminded me about thanks

[@mark_osborne]

Yes those were used for example on 260 Olds V8's ! I'm guessing GM wanted to keep the refined primary fuel control as the primaries on a Quadra-Jet were by far the best fuel metering on the planet, delivering the best fuel economy of any carb at that time thanks to the triple annular discharge boosters, plus mixture control thanks to the vacuum modulated metering rods (and later electronic feed-back metering rods).... and the 260 had absolutely no use for 2 large secondary barrels !... so yeah ! .. and if by chance bean-counters made the call (as opposed to engineers) good for them :-)

[@davidmckinney6577]

I've got a 78 Cadillac it has a rough rolling idle I've rebuilt the carburetor it takes the gas good but has a rich unstable idle and it will quit running I'm thinking the top of warped like you said.

[@mark_osborne]

it could be. Get up on your knees and take a look down the primary bores as she idles. If there's fuel dripping from the nozzles, you must figure out why. Could be warped top plate, could be bad float adjustment

[@davidmckinney6577]

@@mark_osborne thanks buddy I will get it out of the garage tomorrow and bring it down and check it out I'll let you know what I find

[@tinocairo6605]

Not a big fan of Quadrajet carbs but it’s great to learn how to rebuild one.

[@dennisscars8500]

The adjustment screw you reference at 10:57, all the manuals only say put back where you found it. But mine was screwed all the way down which doesn't sound correct. Any advice on where to start it if "that guy" beat you to it? Thanks for the great tips.

[@mark_osborne]

You are confusing me 14:13 is the end of the video Try again

[@dennisscars8500]

@@mark_osborne oops, time for those glasses. corrected. 10:57

[@mark_osborne]

@@dennisscars8500 Ahhh yes yes. I do not know the factory adjustment but all that will happen if it's screwed all the way "in" is it will be "leaner" at high intake vaccum (cruising under light throttle). Set it about 2 turns up, you should be good.

[@dennisscars8500]

@@mark_osborne Perfect, thanks for the help and great videos.

[@esmon5358]

I’m surprised you didn’t bring up the fuel bowl wells leaking. I love quadrajets.

[@mark_osborne]

While I'm aware of the issue, and the ' black sponge thinggy' that comes in most kits to combat the leak, I'm personally unaware of any single Q-Jet that has suffered from the problem

[@jtp682]

Very good video! I need some advice on something. I recently bought an 1986 chevy truck with a V6 4.3. It has a propane system on it and the original carburetor is no where to be found. I have a 78 quadrajet that I just rebuilt and would like to install it. the truck intake manifold is the original four barrel spreadbore quadrajet carburetor set up. Also this engine has the electronic spark control distributor without the vaccum advance. if I put this 78 carb I got on it do you think it will work just fine?

[@mark_osborne]

Yes yes yes - no reason it won't. Hydrocarbons are Hydrocarbons :-)

[@jtp682]

@@mark_osborne awesome, thank you!

[@youthmanrecords420]

In 1986 they would be throttle body injection. In 1984 the Chevy C/K series had a carb and TBI option. Some carbs still remained in 85 but by 86 carburetor was phased out and what most would consider a TBI was standard in the vehicles going forward. And after that OBD 1 followed

[@rollin19]

Hello Mark I just took mine apart and cleaned it but I wasnt gonna go into changing out the throttle bushings since you risk snapping off the screws. I wasn't gonna take the electric choke off as well but now you showed why you should,I think I will. The secondaries on bottom when the primaries are opened up at full throttle are only at 80 degrees. Should I adjust the secondaries or is it set to factory specs,if I need to what are some ways I can adjust it to open at 90 degrees? I know you mentioned the spring tension but I am new to this since it will be my first rebuild I have ever done. I am not new to working on cars I just never got into rebuilding carbs.

[@mark_osborne]

No reason to remove the electric choke as it does not rely on "vacuum" to draw hot air, the electric heating element relaxes the choke spring, so save yourself the trouble. Completely normal for the secondaries to open 80 degrees. Yes, just leave the throttle bushings go unless they are so worn out you can't. You are correct, you will likely break off the screws. Hope you got this note in time I have been out of town. You only need to adjust the spring tension if it is "bogging" when you open the secondaires ( too lean).

[@rollin19]

Hello Mark Osborne,It's good to have guys like you around to fix this old stuff and keep it going or to answer the finer questions. I've watched a few videos on how to rebuild the quadrajet,so many things are mentioned but so many questions are left unanswered. You are a great help to me. Thank you!!

[@grand73am]

You're probably done by now, but just wanted to let you know that you can take the primary plates off without breaking the small screws. They were "staked" on the ends from the factory, so you just grind off the tips, all the way down to the shaft surface, preferably with a carbide burr on a die grinder or drill. Then the screws won't break when removing them. But back them out slowly and carefully nevertheless. A primary throttle bushing kit is available at cliffshighpermance, and contains bronze bushings and new screws for the plates. Installing the bushings requires using a special drill bit to properly size the holes for the bushings, and Cliff sells it too. Makes the job easy.

[@TrentGustus]

I just rebuilt mine from a 77 olds 455 motorhome, someone had the spline off the choke shaft and I had to guess on repositioning it, it would be great if you could do a video on how it's assembled and how each stage of it works. I pretty much guessed on its position and I think I have it right. But I'm not sure

[@mark_osborne]

I've never seen or even considered pulling the spline off the shaft. However, if you do a normal choke adjustment, meaning, cold, you rotate the choke spring until the choke 'just closes', you should be close. If she seems a bit lean, give it a tiny twist -tighter. If she seems a bit rich after she warms up, do the opposite

[@gustavette8487]

What a great video. Can you provide more details on how to get the best gas mileage for a daily driver?

[@mark_osborne]

There isn't much you can really do if it's a stock carb with proper jets and metering rods sized for the engine. Advancing the timing a few degrees can help at the risk of spark knock. Make sure your mechanical advance is working properly and the vacuum advance is functioning and has the proper vacuum source connected to it.

[@jeffyork9389]

Awesome incredible video. You have a great knowledge and why to communicate it clearly. I recently installed ceramic long tune headers on my Q jet 454 in my ( dont laugh) restored 1977 Airstream motorhome. ( she is beautiful) along with the headers I put on 3 inch exhaust and flow master mufflers. I am concerned any correct air fuel mixture and I think I may be a bit to rich. She runs great my my fuel economy went down and I am afraid of over washing the cylinder walls. I tried adjusting the air mixture screws with a vac gauge but it seems lie a less than accurate method. I watched a guy adjust a carb on your tube using a vac gauge and then using an O2 sensor with a AF gauge. HIs results with the O2 showed he was way off using the vac gauge method. What is you suggestion on correctly setting the mixture ? Is there more to it than just the idle mixture ? How do I know I have the correct mixture and highway where my RPM is about 2,600 at 60 mph .

[@mark_osborne]

Jeff, email me at [e-mail], we can chat on the phone, too much to type

[@jeffyork9389]

@@mark_osborne thank you Mark Osborne. I sent you an email.

[@deankay4434]

Mark, you are bringing my memories as I’ve done that many Q-Jets as well as Fords VV7200 & VV7400 while dealers where replacing them the the old two barrel carbs out of warranty. Side draft, Solex, Mikuni and the Chrysler group of Mitsubishi carbs with the wax pellet used to open the choke. Later, they placed a hardened steel cover that I removed to adjust the screw held by a lock but...the one with Red Epoxy on it. Omaha has Offuit Air Force vase. Guys that had the rank brought cars back from all over the world especially from Italy. They drove me crazy. Here’s one for memories; Remember the “Delco” ham cans? The little red string you pulled to open a can of bushings, brushes, all kinds of small part use to rebuild stuff. Remember pulling a distributor during a tune-up? That’s us. Best luck as I truly enjoy your videos. Boy the stories we could tell. Blessings on you, your family and all.

[@mark_osborne]

I am sorry Dean I meant to reply to this long ago and it got away from he. YES those stooping hardened cans ... what were they thinking ? Sadly I never experienced a Delco Ham can but it sounds cool. You probably gained a ton of experience messing with the Italian cars ! Thanks for the awesome reply :-)

[@frankbrochu8829]

I just got a GMC C2500 1984 gifted to me and all of a sudden the truck stopped on the side of the road, if I poor gas straight down the carb it runs then dies, so I pulled the fuel line, turned the truck and fuel is coming out of the said line, changed the fuel filter and still no luck getting any fuel to the carb, said carb is a Rochester 17080212. Bare with me I don't know much about carbs and no one around my area knows how to work on them anymore. I'm considering buying a carb rebuild kit and do my best at putting it back together, but before I go in there I was hoping maybe you had some suggestions. Cheers

[@mark_osborne]

There is a small filter in the carb- it is inside that adapter that the fuel line threads into. That filter could be clogged. Takes a 1 inch wrench do undo the adapter once the line is off. Also (rare) the needle or float could be stuck closed. Very rare tho.

[@frankbrochu8829]

@@mark_osborne thanks for the quick response, the filter I have changed is the one in the carb, the only one I found as a matter of fact, so my guess is that I need to open up the carb to go look at the float and needle, I will be ordering a rebuilt kit in that case and I will watch and rewatch your videos to make sure I don't fuck it up haha

[@mr_dill_pickle5242]

GREAT video, I love having You Tube because there's always a professional around willing to give us non-pros some help. Out of curiosity do you have any recommendations for rebuild kits? I'm about to tear into mine and have been looking for a good one. Thanks again!

[@mark_osborne]

Thanks for stopping by and checking out the video. Honestly I just buy whatever rebuild kit is available, all you are going to use out of it are the gaskets and accel pump rubber, basically. If you need a float or choke pull-off, they will be sold separately. Back in the day I used to buy 100 upper and 100 lower body gaskets and a bag full of accelerator pump gaskets at a time from the local re-builder, but I have since used them up. I got the kit for this one from O'Rielly, it has gaskets that cover many models. Like $20 bucks.

[@Spiritof_76]

Kits with the most parts: Cliff's Performance, Quadrajet Power, Mike's carburetors, The carburetor Shop Eldon, Mo..

[@gustavette8487]

Excellent tips! Thank you. What would be a good source for re-build kits?

[@mark_osborne]

O'Rielly sells a kit that covers many Q-Jets for a little over $20

[@Spiritof_76]

Kits with the most parts: Cliff's High Performance, Quadrajet Power, Mike's Carburetors, The Carburetor Shop Eldon, Mo.

[@gjjcgmail9930]

@@Spiritof_76 Thanks for the great info!

[@rockerbigjoe5711]

I have a quadrajet with its own Secondary pulloff. Even under full vacuum it doesn't seem like it can even open the secondaries. I also have a electric choke. Do you have tuning video's? How can I tell if my secondaries are opening under the proper load?

[@mark_osborne]

That secondary pull-off will relax one you mash the throttle and the intake vacuum goes away. Just check it with the engine shut off, you should be able to push the secondary air door open. If not, something is wrong. Not really sure how you can tell if they are opening other than the "sound"- depending on the engine, it is an unmistakable "roar". I have one other tuning video on how to adjust the secondary air door tension. If it was me, I'd remove that secondary pull off and simply adjust the tension on the secondary air door (if needed), you probably won't even need to adjust it, I'll bet she runs just fine

[@savagenyeste6026]

Awsome vid

[@richard8024]

Picked up a Quadrajet carb at the Pic a Part (cheap) came off 1970 El Camino with a 350. I ran the numbers and it came back a California Emissions carb . I did a little research and it looks like that carb came with smaller jets and rods to meet emissions . I want to put it on a 350 Chevy so what would be the stock jets and rods size for it and what's the difference between the two carbs. Thanks

[@mark_osborne]

I have no clue. Stick it on and see how it drives. If it seems "lean", try some smaller metering rods. I've even taken metering rods and very carefully ground them down a tad on a high speed bench grinder. Don't tell anyone !!!!!

[@armandocandelaria8461]

Very nice you doing this, you have any carburetor repair ready to go for sale 350 motor

[@mark_osborne]

I'm sorry, I do not - I rebuild them as they come in

[@franciscotrujillo4961]

One more question friend, I'll tell you, I have a Rochester Quadrajet carburetor and I want to change the primary nozzles along with the primary needles, and since there are different numbers of nozzles and primary needles, I have to deduce that depending on the number of nozzles, I must set the needle number equal to the nozzle number? I mean, if I put number 0.72 primary nozzles, should I put number 0.72 primary needles? I understand that in this way, the idling engine has the primary nozzles blocked with the primary needles, since they are of the same diameter, and that when accelerating and losing vacuum, the primary needles begin to rise, allowing fuel to pass to the primary jets, is that correct? all the best

[@mark_osborne]

I have never played around with changing nozzles, so I can't speak to their relationship (in size) to the primary needles. The primary needles do not block the jets, rather, they are a partial restriction. You are correct when you describe the operation of the needles in relation to intake vacuum

[@10calrockytop]

Mark, loved your detailed video. I have a problem getting the primary metering rods out to rebuild my carb. The piston seems to be stuck in the down position and there is no space between the two bores to pop the collar off. This carb should be original to my 1975 vette carb # 7045222 R6. Any ideas?

[@mark_osborne]

I just grab the metering rod holder thinggy that is sticking up and yank it out with pliers. But if it's corroded/stuck then spray some WD40 or something down in there to hopefully dissolve the corrosion a bit

[@benheffley6496]

Do you have any videos of rebuilding? Or a video of tuning when you first put it on? About to rebuild my first and could use the tips. Especially from you

[@GlennLittleford]

Great video, thanks. The primary metering rods adjustment screw ( between the metering rods piston and the fuel inlet seat ), any suggestions on a setting to start with? I've removed mine and forgot to count the turns.

[@mark_osborne]

Bottom it out and wind it back up about 3 turns- that will get you pretty close

[@guy1704]

Thanks for all the information. I’m trying to find out how to initially set the height of the metering roods. If you could tell me how I would greatly appreciate it. Thank you.

[@mark_osborne]

Are you talking about the downside stop ?, the brass screw that limits the downward travel ?

[@guy1704]

Yes. I screwed up and took it out. One of life’s lessons learned the hard way

[@mark_osborne]

@@guy1704 Sorry. I'd put it back in, screw it all the way down, then back it up 2-3 turns. Put the metering rods back in along with the spring and see where they stop. They should press down and almost stop before bottoming on the brown plastic cup/retainer that presses into the bore. Hope that makes sense. If it doesn't let me know. I'll shoot you my phone number.

[@victoroneill7924]

If the threads in an idle screw hole are slightly damaged and the idle screw won't go in all the way in can you run tap through to straighten up the threads?

[@mark_osborne]

I never tried but I'm sure you can !

[@Black0ysterPearl]

I hear that older carbs need some modification to be able to properly burn the new crap high ethanol fuels that have a different specific weight/density. I've got a '69 Buick Electra 430cu.in that doesn't seem to like the new fuel no matter how much I tweak it. Any ideas? I like my Quadrajet and want to keep the car as stock as possible. Right now, it's hard starting, requiring sever pedal pumps to get it running.

[@mark_osborne]

I am sorry you are having trouble. Personally, I don't believe that the 10% ethanol is causing the problem. It's just too insignificant IMO. Sure, it can hurt certain rubber components, but there's nothing in the carb that would be effected to my knowledge. Sorry I can't be of more help. I've got a 403 here that runs just great on the crap fuel :-)

[@yazmingamboa6834]

How about a rebuild on a 2 barrel quad? Any pointers will also be immensely appreciated. Thanks Yazmin Venice Beach 🌴

[@mark_osborne]

Everything in the front half of that carb is exactly the same as what's in this video- no difference. You're just missing the rear 2 barrels.

[@GarthThomson]

Great video, so much knowledge and experience! I just rebuilt my Qjet and it’s great except for the secondary pull off relay holding the secondary choke flaps closed. I’ve disconnected and temporarily plugged it (runs beautifully now) but I’m at a loss as to why it’s like this? Will the pull off relay release on hard acceleration? Doesn’t feel or sound like it on test drive. TIA

[@mark_osborne]

My suspicion is it's a back-up government required emission device - other than that, I'm with you, a complete mystery. Yes once the vacuum goes away, it releases. That that stupid thing off and throw it away..lol

[@GarthThomson]

Mark Osborne haha yeah I’ll leave it disconnected and have a look what it does on hard acceleration in the driveway (sorry neighbours) and maybe next time it’s on a dyno observe what it does there! Thanks again for the fast response and great videos.

[@brianeidmann5941]

Taking you up on posting a comment with a quadrajet problem. I rebuilt mine, but did not file it down like yours unfortunately. I just saw your tips today. Anyway, my carb runs a little rich, so I hooked up the vacuum gauge to adjust the mixture screws, but when I adjust them, there is NO change. I can back the screws out and screw it all the way in and there isn't much change - no drastic change anyway. Any suggestions? It is a marine quadrajet - probably doesn't matter. The exhaust smells rather rich and I can see a little fuel maybe in the exhaust water discharge, but it seems to idle ok. Not as nice as my other engine idle, but it does idle alright. Also, very, very hard to start cold, but once it gets going, it is good. Maybe they're related...I dunno.

[@mark_osborne]

When you run those mixture screws in you are cutting off fuel to the idle circuit (as you probably know) and it should get so lean it stumbles. Because that's not the case, I suspect you're getting fuel from somewhere else and the most likely culprit would be if the fuel level in the float bowl was too high. Try looking down into the discharge boosters with a strong flashlight and see if you can see fuel dripping from a booster, check the secondary side too. A hard cold start (if carb related) means either the accelerator pump isn't shooting fuel when you pump the throttle, or the choke isn't closed all the way.

[@davidbowers6005]

@@mark_osborne I've got the same problem. I checked the float, now I'm looking for a vacuum leak. Only getting 14" of vacuum

[@shawnhostler1514]

My q-jet leaks out the well plugs when it sits. Have to add fuel to start it. Do I epoxy them? Replace them?

[@mark_osborne]

Take it apart, place the center section (body of the carb) upside down on a work bench covered in a thick towel. Then, take a small flat hammer (not a ball peen hammer) and go around each well plug and slowly hammer over the aluminum that holds the plug in place. Be careful, go slow, just try to do an even job all the way around each plug. I have had success doing it this way. You could also apply some gasoline resistant epoxy (as you suggest) over the plugs after you've given them the hammer treatment. Do NOT try to replace them, you will destroy the carb.

[@shawnhostler1514]

@@mark_osborne ok. Thank you very much for the info

[@setevn11]

I have a carter quad and was wondering what the square hollow is for on the back outside of the main body? Maybe .5 inch wide and 1 inch tall.

[@mark_osborne]

Some air filter assemblies had a tang that would index into that square hole holding the filter assembly in the proper rotational location

[@howardhagadorn9443]

You said some OLD stuff, so I was hoping I was gonna get some learnin lol I have a 52 Olds with the Qjet 7004300. I bought a kit for it and put it in and found before putting the lid on it that some idiot had taken the new accel pump out and put his old one back in my kit. It's got the old leather style accel pump and I'm having problems finding a replacement. I've checked my float levels and replaced one of the old brass floats but I'm still leaking gas somewhere and is always flooded unless it's sat for a long time in which case the float bowl seems to be dry..........

[@mark_osborne]

Those old leather accelerator pumps were not all bad and seem to last forever. Did you get the little black sponge that fits in the cavity between the main body and the throttle plate ? It's designed to stop the main wells from leaking gas down into the intake manifold. Start the engine, let it warm up, shut it off, wait about 6 hours then unbolt the carb and lift it straight up a couple inches and look to see if there are drops of gasoline hanging from the bottom of the carb. If so, that's the problem.

[@howardhagadorn9443]

@@mark_osborne I got nosing around to see if I could find out if it had the well plugs that seem to get a lot of noise about leaking. Little black sponge eh? It's been a while so I'm not sure at this point. Thanks for steering me in that direction

[@dustindustries42]

Hello so question I ha e rebuilt my q jet worked great for several days. They had it tuned at a shop and now it's flooding. I saw another vid with a q jet on a dyno and he was very adamant that with these new fuels you need to have a regulator with it set at 3lbs instead of stock 6 or 7 from the mechanical pump. Do you agree? Carb has had an issue with flooding and dying intermittently. Runs great gets warm then ideals and dies. Also when it gets warm it seems like the tune goes out the window and the fast ideal screw is out of whack where I have to tighten the screw back up to have it run. Anyway, I'm going to tear it back apart. If you have any questions any other tips would be greatly appreciated. Cheer thanks for sharing your tip and tricks.

[@mark_osborne]

I have never heard of having to reduce fuel pressure because of the addition of ethanol. Can't imagine why. But I'm all ears. Ask him why. In my opinion, there is only one reason the carb is flooding IE: the needle is not shutting off the fuel flowing into the seat. Why ? The most common reason is simply some tiny piece of debris caught in the seat (that got past the filter). Rare, but possible, a bad float. Try putting an extra filter in-line. You could have junk in the tank. As far as the tune goes, it's impossible for me to assess that situation from (over here)

[@dustindustries42]

@@mark_osborne kzbin.info/www/bejne/mWmzXmuYmbZ9gdk Here is the link to that guy who is talking about file pressure on a Rochester

[@SerpentineUsurper]

LEGENDARY 🇭🇲

[@jpninety3]

I will literally pay you to rebuild mine. I ordered a remanufactured one from Autoline and it was the most half assed garbage carb on the inside I could ever imagine seeing. The guys didn't even have a hanger for the needle. The needle was just sitting in the seat causing the carb to flood...majorly. worst 300$ I've ever spent. My carb on my 73 delta88 is overdue for a rebuild though, That's next on my list being as buying a remanufactured one was a big mistake.

[@jamesahr2634]

Don't forget the throttle shaft bushings. They wear out causing vacuum leak.

[@mark_osborne]

Yes, great tip. Funny, I've been through probably 1000 of these carbs over the years and never addressed that issue mostly because if you attempt to remove the throttle plate screws they tend to "break off" and you're left with a piece of unusable trash. A couple times I was forced to adjust some secondary throttle plates and was lucky enough to get some #6 machine bolts with nuts back in place, along with red lock-tight after breaking off the original throttle plate screws. Thanks for the memories !

[@grand73am]

@@mark_osborne Yes, the small screws holding the plates are staked on the ends, so those end tips must be ground off to safely remove the screws without damaging the shaft or breaking off screws. And primary throttle bushing kits may not have been available long ago, whereas now they're readiy available at q-jet parts dealers like cliffshighperformance.

[@reggiesasser3871]

Thank you so very much for sharing your knowledge. I have a 1967 7027202 quad that was missing the power piston. The kit came with the plastic ring however there is no counter bore so the ring will not press in. For this carb. is the piston held in w/ the gasket and air horn only? Reggie S

[@mark_osborne]

Yes, you have to hold the piston (accelerator pump) down into the body, while slowly lowering the gasket and air horn down over it. You have jogged my memory with your question. I have often taken a razor blade and cut out the gasket (in a circle) above the accelerator pump (piston) so the gasket can drop down onto the body before trying to put the top section in place. It makes it a bit easier. (not having to fight with the gasket as well as the top section while holding down the accelerator pump)

[@grabir01]

My Quad is not fat enough. I have a 69 Buick Skylark with the L77 350 4B motor 10.5:1 compression and a Crane cam. Runs like a scolded cat! Awesome power! Big block power!! My problem is once the motor is good and warm, it wants to ping some unless I back off my timing a couple of degrees. Doing this loses me a ton of power. I can not find Ethel fuel any more as 91 is the best to be found at the pump. I might put a gallon or 2 of E85 which seems to help a little but I do not like E85 because of its hydrophilic properties. My thought to overcome this ping which is only after it is warmed up and under load at lower rpm is to fatten up my carb as mpg is not a concern for me. IS there a way to fatten up this carb? Do they have jets for these quadrajet carbs? Slow jets and fast jets? I would like to fatten up both circuits to the next size larger and see if my ping goes away.

[@louiscyphre6049]

Working on my E4ME CCC carb on my 84 camaro again. I tell ya, without the gauging tools or basic settings it can be a pain. 😩 Great carbs none the less.

[@mark_osborne]

Yes they have a fair amount of things to watch, I "count" the turns of the mixture solenoid screw when I back it out.

[@louiscyphre6049]

@@mark_osborne I wish I did the first time I took it out, but the instructions say 3.5 turns from lightly seated. Because otherwise if you can't get the gauging tools that no one sells anymore your "screwed" lol. I finally did the air bleed valve too (took the plug out and new o rings) I'm hoping that was my richness problem I've been having cuz everything else was working from what I could tell.

[@mark_osborne]

@@louiscyphre6049 good deal. Were you able to remove the restrictor caps that cover the idle mixture screws?

[@louiscyphre6049]

@@mark_osborne yep

[@louiscyphre6049]

Unfortunately one of the mixture screws was seized and the head broke off so I could only set one of them. If this last rebuild makes it run better I'll just end up buying a remanufactured carb, even though my carb only has 116k miles on it it's pretty rough from sitting before I got it.

[@dansmith6990]

Hey Mark, great video! I just rebuilt my quadrajet today but the included instructions didn't have my particular model# to set the float... what height is a good one for my old 1984 motorhome quadrajet? Also, can you please elaborate on setting the idle screws? I didn't mess with mine, only cleaned them and put them in the way they were before but I'm sure it's running too rich

[@mark_osborne]

Basically, if your float is new (unbent at the adjustment point), install it and push down on the needle end (so the needle is shut off). The float (itself) should be parallel with the top of the carb. If it's not, bend it at the adjustment point. If your carb has not had the idle restrictors drilled out, your idle screws are only effective until about 3 turns out. Beyond that, they do nothing. So start at 3 turns out and you can go in a little, perhaps down to 2 turns. Play around with them until you're satisfied with the idle. You can tell if you're lean by placing your hand over the air horn and slowly restricting the air going into the engine (causing some fuel to be sucked out of the main nozzles). If the idle picks up, you're lean. Back the mixture screws out a bit. But like I say, anything past about 3 turns and you're doing nothing.

[@marald64]

Mark, I've found this video to be very informative...Thanks . I do have a question regarding the quadrajet living under the dog house on my 1985 Chevy P30 motor home chassis, which I'm in the process of rebuilding. Are there any additional tips you can offer regarding a balance of drive-ability and economy, as this fleetwood behemoth doesn't get the greatest mileage, nor power when you need it. This carb sits atop a chev 454. Any help would be greatly appreciated...Marty

[@mark_osborne]

Sorry sorry - nothing that I am aware of will give you both better drive ability AND better economy. They are exclusively at odds with one another :-(

[@joseantoniomendezhumero9428]

Dear sir: I own a 1977 chevrolet Corvette with the L82 engine After suffering a gasoline fire in my garage due to a broken glass bodied fuel filter. Needless to say I had one of the most scary moments of my life until I was able to put out the fire. Anyway the damage to distributor, wires, carburettor was extensive. My mechanic and I decided this could be the time to make a long needed overhaul of the engine and I went ahead and bought a new distributor and a rebuilt quadrajet carb. My problem now is as follows: Thr engine starts easily and after warmed up and going to idle it dies. Something looks wrong with the idle circuit.The only way to keep it running is to accelerate to 2000 rpm or so What do you make of this. Your experience is invaluable for us. Thank you in advance

[@mark_osborne]

Yes, I agree, the idle circuit is most likely the problem. As a test, place your hand over the carb inlet, slowly restricting the air flow at an idle, and if you can correct the problem, the idle circuit is almost certainly the problem

[@georgemccune8502]

Great video! Got any tips for stopping the MCS from ticking? I've heard this is normal on the 87 Chevy's

[@mark_osborne]

It's supposed to 'tick', it's a duty cycle solenoid - the longer the pulse width, the leaner the mixture and vice-versa

[@lau12342]

Good info! I have a 76' Chevy truck Q-jet and it has a warped air horn (approx 1/8" from corner bolt hole to sec. rods area). Do you think it could be repairable? It had no idle and been sitting some time... Thanks!

[@mark_osborne]

I think so. grab a large coarse file and just work it, trying to focus primarily across the front (where it's warped the worst) first. Then slowly work it around and make sure the file is hitting across the entire top. Don't worry if it's it's a tiny bit spotty, meaning, not hitting as hard everywhere. You're just looking to get it flat, not perfect. You're not by chance related to a Bob (Robert) Jokinen who lives in Michigan ? I went to college with him back in the 80's. We sort of lost touch

[@lau12342]

@@mark_osborne Okay, I have to try and see how it turns out. Thanks! I live in Finland so I'm not close related but he's grand parents or great grand parents could be from Finland. There are many Finns livin in the lakes area US and Canada.

[@Blakep7704]

What would cause my Q-jet to run my primary boosters to drip @ an idle? I can't run my throttle blades to square my T slot before it will die so i have to speed up the idle screw. What would be the solution?

[@mark_osborne]

Is this a large displacement engine ? I assume you do not have restricted idle circuits (starving for fuel). I assume your float is set to a reasonable level. Given that, if you need that much throttle opening to allow the engine to idle, then I wouldn't worry about it.

[@Blakep7704]

@@mark_osborne yes mark, chevy 396BB 12" of vacuum at idle. The problem is i have no idle screw adjustment.

[@mark_osborne]

@@Blakep7704 Ok got it. Large cam, large engine. Completely normal. No worries. Take your hand and slowly restrict the air flowing into the primary side (hovering over the choke), if the idle picks up or gets smoother, you have restricted idle circuits. If the idle doesn't change, or gets worse, you are getting enough fuel. But either way, with only 12 inches of intake vac at an idle, you have a bunch of reversion and yes, it would be normal to see fuel dripping from the nozzles

[@scottsarver779]

I have a question and hoping you can help me. Just bought an 84 ss monte with a quadrajet. The secondaries do not work because the cam on the metering valve hanger is gone. You open the secondaries and the hanger does not move at all... cam gone. I'm going to purchase one but no one seems to show how you get the air door butterfly shaft out to replace the cam, which is in the middle of the shaft. I just want to repair the carb for now as I don't plan on having this setup for long. Any help is greatly appreciated!

[@mark_osborne]

Because the cam is missing, we know the screws that attach the butterfly(s) to the shaft will likely come out (because they've already been out), and that is the biggest challenge to removing the shaft. (getting the screws out of the butterfly(s)) Beyond that, you'll have to study the return spring carefully before disassembly so you know how to put it back together. With that said, you should have no problem putting the cam back in :-)

[@scottsarver779]

@@mark_osborne ok so take the secondary pullooff off. Remove butterflies and shaft should come out. Thx for mentioning the spring and your help!

[@mark_osborne]

@@scottsarver779 oh, you might have to take the top of the carb off and put the cam in from the bottom side, I can't remember

[@kainestefaniak2751]

What about warpage? Is there a tolerance I can use, I tried to unwarp using heat and trying to finesse the body by assembling it no gaskets and such. Worked abit but my secondary flap in the airhorn is getting hung up now in the process of "bending" things but I still have a high spot in the middle section ( housing I suppose) should I try individually bolting stuff to a bench with heat and apply force on the centres?

[@mark_osborne]

Usually you must file the opening where they secondary air doors are catching. I place the entire top section upside-down in a vice and take a large file and make passes until I'm just tickling it in the middle. They worst part will be where the 2 front bolts go through.

[@kainestefaniak2751]

@@mark_osborne the flaps are only hanging up due to what I did they were smooth as silk otherwise it's the rod itself is binding and moving in its groove but I think flattening it will help. I will try bokting down to a very solid piece of timber w heat and try again and if not I'll try that method

[@mark_osborne]

@@kainestefaniak2751 Yeah you may have this thing torqued out of shape. They typically only warp in the front 1/3rd due to the 2 large front bolts- which is usually correctable with a large file. Sorry you're having so much grief

[@kainestefaniak2751]

@@mark_osborne as expected with older items, no problem I will slowly get it, I really appreciate the feedback and will be watching again when i get it sorted. Carby is supaa clean just waiting on some parts. Wanted to help the old man getting his hq Ute running. Seen a few different methods but seen you were fairly active in the comment section so multiple opinions is always thought of and appreciated

[@harleys2u]

Here's my situation. I am helping a friend with his motorhome that has a 454 and a q jet. It's an 87. I have mediocre mechanic skills including engine rebuilds and a few ASE certs. My q jet knowledge is very limited. The issue is his vapor canister was filling with fuel. I know about the purge and vent valves, which appear ok. The tank pressure valve is questionable and I don't know if his model actually has one. I am suspecting that the vapor hose coming off of the carb at the bowl vent nipple is supplying this unwanted fuel. My guess is what I need your opinion on. My guess is that his float is bad or the needle is stuck open and allowing the bowl to pressurize with fuel and exhausting it through this hose, thereby flooding the evap canister. What do you think? We will remove the carb top plate tomorrow to verify the condition of the float and needle parts. Does my theory hold fuel, I mean water? Thanks for you informational video. Kramer.

[@mark_osborne]

Just pull the hose off the carb and see if gasoline is dripping out of the open tube. I doubt that is the problem tho because if the fuel level was that high in the bowl, you'd have (rich) running issues. I have seen flooded canisters over the years but never really sorted out the cause, usually we would just block them off and call it a day

[@alejandrohernandez-co8zy]

mark Hello, greetings from Venezuela, what could I do to save fuel? I have a dual jet but it is a dragon, yes it canbio chicler and how could I lower consumption? What do you recommend? Greetings and thanks for your help. You are a master in this I congratulate you I also discovered when I was cleaning it that it did not have the control ball that goes under the screw that you explained what problems it brings me that increases the consumption of gasoline for not having it

[@mark_osborne]

The check ball allows the accelerator pump to function properly, it will have no effect on fuel consumption. Make sure your float is not set too high, if it is, you can get 'spill over' effecting fuel consumption. Beyond that, there's nothing easy you can do that will cause it to use less fuel. If you have an Oxygen sensor make sure it's working and plugged in.

[@terrycain1920]

I've fooled with Quadrajets for years also. The newer ones have me puzzled in that on the front pass side across from the accelerator pump is a BIG black plastic "cup" (if you will for lack of a better word) which I'm having a hard time understanding what this is engineered into carb for. Could the cup also be left out to help with more fuel storage since Quadrajets have a small fuel/float bowl area.

[@mark_osborne]

Yes yes, I see absolutely no reason you can't leave it out. It never made sense to me why it's there. In some of the Cadillac carbs, there is an altitude enhancement thinggy that fits into that pocket, and it's adjustable.

[@jrgiltrdo]

Mr Mark I rebuilt Rochester Quadrajet put it all back together but would not stay running i could here a vacum leak but i can"t not find it.'

[@mark_osborne]

Take a piece of vacuum line about 4 feet long, put one end of it at the opening of your ear, take the other end and start moving it around the base of the carburetor, intake manifold, etc. You will instantly find it.

[@13mopar]

trying to get an old SBC running after a decade of neglect, part of the plan is rebuilding the carb. curious if there is anything i should be looking for that says i should chuck it in the bin and find a different carb?

[@mark_osborne]

There are many more videos similar, if not better, than mine on this wonderful platform of information sharing. Use them to your advantage and bring your carb back to life !

[@georgekazimierczak9294]

Maybe because there 🤔 where millions q jets out there ,that you lucky enough to have worked on ! Thanks for sharing 👍 information, young whipper snapper need help.

[@lindseysteele1436]

What about the ideal compensation on the back of the rodchester

[@mark_osborne]

You see them on Cadillacs, but very rarely used on other models

[@bobc.5698]

Have you ever had to file the secondary doors down to keep the from sticking?

[@mark_osborne]

Absolutely

[@kevineley465]

Do u hav video on a Electric Quadrajet removed and replaced with the four barrel Edelbrock

[@StarlightWorkshop0z]

Hi Mark, great explaining. I have a qj on an aussie holden v8. I just set the choke to lean as we dont get that cold here. Its been running rich and chewing fuel. I noticed the secondary air flaps on top seem to be fouling on the carby body or shaft. Also my secondary vacuum pull off isnt working as i tried to suck test it. Nothing. Any advice please? New fan down under

[@mark_osborne]

The air flaps are hitting the top because the top 'distorts' over time from the pressure of the screws. If you look close, you can see where the door hits. Just file the top in that area a bit with a rat tail file. Stuff some paper towel down into the barrels first. As long as your primary pull-off is working, you're good. The secondary one is just a back up from what I can figure. As far as it running 'rich', are you certain your choke is completely opening ? It's common for chokes to get lazy and WOW will you eat fuel. The heat (exhaust) cross over in the intake can get plugged with carbon and your choke won't get enough heat. That's just one example of WHY a choke can get lazy. Check those things and let me know. Your choke should completely open with zero tension, and that will also allow your secondaries to become operative.

[@StarlightWorkshop0z]

@@mark_osborne cheers chief, i will look into it and report back. 👌👍

[@richardriehle4159]

interesting . thank goodness for efi.

[@mark_osborne]

Hey Richard, did you know the next generation Q-Jet employed electronically controlled metering rods, a 36 mhz computer, throttle position sensor, oxygen sensor, MAP sensor and coolant temp ? That's right, it used all the same inputs as GM's first DFI, only instead of driving fuel injectors, it used the feedback loop from the O2 to PWM (modulate) the metering rods in attempt to maintain the proper fuel/air ratio. The system worked amazingly well ! However, once DFI (throttle body injection) hit in 1982, the complexity (vacuum lines, wires, etc) was vastly improved.... and the beloved Q-jet was part of history

[@richardriehle4159]

no, i did not know that ! that's really interesting . what years did gm do that system?

[@mark_osborne]

@@richardriehle4159 To my knowledge it started in 1981, and ran thru 1988, the final year for passenger car and light truck applications. Everything after that was EFI. BTW, they referred to that carb as the E4ME :-)

[@ApostleDavids8w]

I could use some help. And thanks for the tips. I have 3 quads that came off a 305s. I want to rebuild 1 and put it on my 496. I’m worried the carb will be to small. Any thoughts.

[@mark_osborne]

Ok a 496 turning 5000 rpm consumes ((496/2) x 5000)/1728 = 717 cubic feet per minute of air. But then we reduce that slightly by the volumetric efficiency. 90% is considered good, so 717 x .9 = 645 CFM. So yes, it will work. But if it's off a 305, the secondary air door is restricted from opening all the way. Just saw off the stop so it flops all the way open (90 degrees) when you press on it. If you're spinning it harder than 5000, you'd probably want to find an 850 Q-jet off an older big block Buick or Olds, but even at that, it will still work just fine if you don't. You'll just lose a little horsepower right at the very top. But nobody should be spinning a 496 faster than 5000 anyway unless you like rebuilding the thing every other week...lol... I've been down the road with those engines more than once.

[@ApostleDavids8w]

Thanks for the reply I ended buying the HR750 quick fuel. But later I like to experiment and mount 2 quads on it. Thanks again.

[@laurensiemens1436]

I have a question. After cleaning the carb can you paint the carb to get a good look under the hood or look at edelbrock

[@mark_osborne]

I've never tried but I can't see why not. I'd start with primer suitable for aluminum (let it dry real good, stick it in the oven at 160 for a few hours) then finish with your color coat. Be sure your color coat is gasoline resistant. A 2 part epoxy might work. My gut tells me you want to "brush" it on because if you try spraying it on, you'll get paint in places is should not be. Stay away from the throttle shaft, choke plate, accelerator pump, any linkage..... If you do, please put up a video of the finished product !

[@markhuffstetler9009]

Are you kin to john osborne who builds 455 Buick motors , Tennessee or Kentucky

[@mark_osborne]

I am not - I bet he's an interesting guy !

[@markhuffstetler9009]

Oh OK , well nice to see you know about the best carburetors I think on the G M automobile, and John knew alot about them also lost of knowledge like yourself.

[@markhuffstetler9009]

Lots of knowledge

[@dougmrak784]

i am on board with this .but mine dies on a slow stop

[@dougmrak784]

but why does it as does every thing else right ...Vacuum stall not set up

[@prestonobs]

Hey mark just got a 85 c10 with a 4.3 with this carb,its been sitting but not that long,what would you recommend?should i clean it or rebuild it,the truck start runs good and idles pretty good but since its been sitting.i dont know just a 17 year old trying to learn,should i mess withit or leave it alone

[@mark_osborne]

Drive it, see what you got. Those old 4.3's with 4 barrels ran good !

[@prestonobs]

@@mark_osborne alrighty what about the granny low four speed those run pretty slow or get up and go

[@juanchoman9824]

I'm really scared to rebuild the truck is running good but I dont know how long it's been on the truck and want to redo everything so I know when it's been done. Am I going to have to retune or do any timing after I rebuild or can I just slap it back on and go?

[@mark_osborne]

Just mark the choke spring to the housing (assuming you have a integral choke). You can count the number of turns the idle mixture screws are turned out and set them back to the same setting if you're worried about that. Beyond that, there is nothing to worry about.

[@rodgerstwr]

I have a qjet with electric choke that's leaking fuel on side near choke. Can I fix it without total rebuild it runs well just leaks.

[@mark_osborne]

Don't know, the float level might be a big high or the gasket between the top and the mid section could be worn out. Wishing you good luck.

[@rodgerstwr]

@@mark_osborne thank you

[@jeremysmith4655]

I'm suffering from hard starting, before and after the rebuild. If it sits for a while I have to prime it. I've read about the well plugs leaking, have you seen this often?

[@timmthirty7928]

My marine quadrajet won't idle at all. Took it apart and rebuilt it cleaned everything reassembled but zero idle. Will run with anything above idle or if choke is fully closed. Btw this is why I rebuilt it in the first place. Ideas? I tried the two air mixture screws and made no difference

[@timmthirty7928]

Any thoughts on the no idle situation?

[@mark_osborne]

Sounds like a blockage in the idle fuel feed circuit. It's not likely in the throttle plate as you can literally see the circuit, rather, almost certainly in the body of carb. I'd take it back apart and using a rubber blow-gun nozzle, blow air down through the holes that are next to the primary venturi (s)- both sides. This is the idle fuel well. Take a small wire and see if you can dig around as well. Also, make sure the top section of the carb is not warped. If it's warped, fuel won't flow properly through the idle circuit as it takes a trip up- then back down through the top plate right next to where the 2 small bolts secure the top plate at the venturi (both sides)

[@timmthirty7928]

Thanks I will try that. I forced carb cleaner through all passages and it seems to flow thru but did not use high pressure. Carb did have water in it and sat a couple years, was a dunked up mess when i took it apart. Good news is everything past idle works great now, don't believe the secondaries worked at all before, always bogged down and had to pump the throttle to get it on plane. Greatly appreciate your insight, great viedo!

[@mark_osborne]

@@timmthirty7928 water is the worst, almost certain there is corrosion in the idle wells. You could try some CLR, squirt some down the the holes into the idle wells and let it sit, blow it out, repeat, you might clear the blockage

[@donjenkins2052]

correct me if i'm wrong, but i was told the quadrajet only came in 750 and 800 cfm. thoughts from you on that.

[@mark_osborne]

I believe you are correct

[@scottwheaton9689]

@@mark_osborne Chevy only used the 750cfm q-jets on their Sbc & bbc motors. It was caddy,olds,Pontiac,Buick that used the largest q-jets (approx 800cfm) on their larger displacement V8 motors.

[@Robin_Gobblin]

Mark, can you give any advice about the hot idle compensator? Information is limited I can’t seem to find anything. Can it be eliminated if it’s pulling a constant vacuum?

[@mark_osborne]

Yes you can block it off by tapping, and threading a bolt into the hole. You'd see them on Cadillacs, mostly. It was used to offset the vapors coming out of the fuel bowl due to high under-hood temps - which caused a rich idle. It provided make-up air. Unnecessary for most applications.

[@PhillyBatts]

Do you rebuild these for people? If so how much would you charge to rebuild one? Great video btw!

[@mark_osborne]

no really interested, but thank you

[@PhillyBatts]

👍

[@kevlar7556]

Hey Mark, greetings from Bolivia. I wanted to ask you if you have any experience in high altitude settings, I live around 13000 ft. above sea level and we are always struggling with getting a/f ratios correctly. Thanks in advance and have a great day.

[@mark_osborne]

I do not but I can appreciate what you are dealing with. Do you have a wide band A/F gauge installed ? You could always play around with thicker primary metering rods (Q-Jet) or smaller jets

[@kevlar7556]

@@mark_osborne thank you for responding, the other "thing" that we have to deal with is incredible high shippings and taxes rates to get whatever so, most of the time, mechanics and enthusiasts only rely on little tricks to make things work. The point that I'm trying to explain are the difficulties we have to go through to get a couple jets and needles to play with and make things right, lol! Have a great day, sr.

[@mark_osborne]

@@kevlar7556 I understand ! You at least have the beautiful Andes Mountains to look upon, I am jealous of your beautiful landscape :-)

[@SlanginBeatz]

Do the jets need to be reset

[@mark_osborne]

Nope

[@edgarhelm3795]

getting ready to do one and I think there is issues with the linkage. The secondaries do not open up. After removing the carb I noticed a lockout for the sec. What is that for? Where do I find the specs for the linkage? Thanks

[@mark_osborne]

It's there to prevent the secondaries from opening while the engine is cold. It's pushed out of the way when the choke opens (fully). You can eliminate the lock out by removing it. Your secondaries will open while the engine is cold, possible "bog"... but it's all good if you are prepared and compensate with your driving style. Once she's warmed up- it's all good. If you want to keep the lock out, just be sure the choke opens all the way once she's warmed up - that will push the lockout out of the way. Otherwise, there are no specs.

[@edgarhelm3795]

@@mark_osborne Thanks for getting back to me. Starting on it today hopefully.

[@ajslawns8393]

what should i look for,.. on the long debated dieseling issue. 84-86 454 bounder breaking bad r.v. that sat for way too long. i may be the first to pull the carb but will know soon

[@mark_osborne]

The only way it can 'diesel' is if it's getting air. So you want to make sure the throttle plates are closing, and especially check the secondary plates by pushing forward on the lever (driver's side of carb). Be sure those secondaires are completely closed and if not, figure out why. It's a common issue. As far as the primary side, just be sure the choke is completely relaxed and the high idle cam is flopping down out of the way and not holding the primaries on a partial high-idle. If all of that checks good, and your dieseling persists, I'd install an electric step-up solenoid on the primary side. You'd see them on Cadillacs, I assume to solve dieseling. They simply pop out when you turn on the key and push the primary throttle plate open to the base hot idle setting. They are adjustable. Then you back off the primary throttle stop screw (driver's side front of the carb) until the throttle plates close completely in the bore. Then, when you turn "off" the key, the step-up solenoid collapses and the throttle plates completely shut off all air entering the engine. You can see the step-up solenoid I'm referring to on this carb on ebay www.ebay.com/itm/17084208-Rochester-Q-jet-Carburetor-camaro-monte-carlo-dtd-2733-Sept-30-83-/202105377408

[@thatswhy11]

Mr. Osborne I sent you the pics you wanted.

[@hansentom50]

How far did you stretch that spring?

[@mark_osborne]

25%

[@hansentom50]

@@mark_osborne thank you

[@garyanderson4462]

Do you have or know where I can get a dash pot solenoid bracket for a 1970 chevy quadrajet

[@mark_osborne]

is this the one that smashes down with fingers onto the front of the float bowl ?

[@garyanderson4462]

@@mark_osborne yes

[@garyanderson4462]

@@mark_osborne yes

[@mark_osborne]

@@garyanderson4462 I am sorry, I went upstairs and looked though all the Qjets on the shelf. I know exactly what you need and would have sent it to you at no charge had I had it.

[@garyanderson4462]

@@mark_osborne try this again, Thank you Mark for taking time to look for me. I appreciate it. I know they are getting hard to fine. love the videos. Gary Anderson

[@PEDDALIT]

What about the problem of gas “leaking” out of these carburetors when they sit for awhile. I’ve been told to epoxy those plugs on the bottom?

[@mark_osborne]

You could - but the problem is rare. Some kits come with a black spongy thing you stuff in the cavity under the plugs. It's shaped to fit in the cavity.

[@PEDDALIT]

Thanks!

[@thatswhy11]

These two green little gaskets, I see where one goes that sits in the bowl part of the carburetor. I'm know trying to figure out where you said the other green gasket goes. Is it right behind the screw and sits in the cavity of the choke housing where the green rod goes through it from the back of the choke hosing? Very good information, but I just need to know about the 2nd little green gasket location in the choke housing.

[@mark_osborne]

send me an email with a photo of the 2 green gaskets [e-mail]