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Is rebuilding the carb myself a bad idea? I dont have any experience rebuilding carbs however I watched a 1 hour step by step video detailing a qjet rebuild and didn’t find it as hard as I expected provided with a rebuild kit. Has anyone ever done this without experience before? Might also purchase Doug Roe’s book for better understanding of these carbs
Last edited by Andrew Anatian; Oct 29, 2023 at 07:27 PM.
You can do it. Be super clean, methodical, take notes and pictures and follow the instructions PRECISELY and in order. Don't skip any steps or adjustments. Check the throttle shafts for wear, if they are worn you'll have a vacuum leak, it may be best/easier to have them professionally replaced if they are needed. Be careful not to strip the threads at the fuel inlet nut.
A cleaning solution and compressed air will be needed.
Replace the float, fuel filter and check the choke pulloff ahead of time and replace if needed.
A small stand will create stability while you're working on the carburetor. I have a wooden platform made from scrap 2"x4" boards. You could also fashion nuts & bolts together to create (support) a free-standing platform - slide the bolts through the base plate holes use nuts to secure (tighten) the nuts/bolts to the carburetor. Liberally spray (soak) everything in the carburetor with carburetor choke/parts cleaner. I have a set of carburetor cleaning wires (needles) of various sizes but I'm not 100% you'll need any of them. Depends on degree of dirt/grime/gum buildup. One of those dental picks (cleaning tools) works nicely to dislodge junk in the corners/crevices & a handful of Q-Tips. Recognize the names of the parts (a diagram helps). I'll provide you w/ a couple basic diagrams & a URL link (below). Essentially, there are three pieces from top to bottom:
(1) Air Horn Assembly, (2) Float Bowl Assembly, (3) Throttle Body Assembly (with a gasket between each). Pretty simple stuff, really.
I suggest you plan to do the entire rebuild in one day. It's not a good idea to leave the carburetor disassembled for longer than necessary. Too great a chance to loose little pieces or forget how it goes back together.
I rebuilt the quadrajets on both my '77 and '78 Toronados. Had never done it before, but it was not difficult, and it's very satisfying when you're done.
There are a zillion youtube videos you can find and watch.
I found this one to be the most helpful. The carb he rebuilds is from a '79 Malibu, but it was very similar to mine.
A pitfall could be disassembling more of the choke linkage on the right side than necessary when replacing seal #50 in VC/Norm's diagram because it usually swelled and caused sticky linkage after submersion in a cleaner. The first few were a challenge. Leaving the carb with the right side pointing upward and sliding the choke linkage straight up replacing the seal and sliding the choke linkage back down worked well for me.
I rebuilt the quadrajets on both my '77 and '78 Toronados. Had never done it before, but it was not difficult, and it's very satisfying when you're done.
There are a zillion youtube videos you can find and watch.
I found this one to be the most helpful. The carb he rebuilds is from a '79 Malibu, but it was very similar to mine.
I don't believe you've stated what the carburetor model number is which currently resides on your intake manifold. Since the Magic Eight Ball thing doesn't work, your absolute best bet is to state exactly what the carburetor number is which resides on your intake manifold. That should be your VERY FIRST order of business since you do have to order a rebuild kit - right? Hard to order a rebuild kit w/o a carburetor number even more difficult to address questions/answers when we don't know the model number.
This is the video i was referring to, do you know how similar it would be to a 1974 442 carburetor?
No, I don't, but I can't believe they're that much different, and any differences are likely to be something you can figure out on your own. The basic design can't be that much different.
I've found Tyler presents a very good & thorough tutorial for a Quadrajet rebuild - he's meticulous & explains things in very reasonable terms. Kick back w/ a large iced tea and enjoy the entire series.
How to rebuild a Rochestor Quadrajet - Tyler's Neighborhood Garage (YouTube)
Over the years I have rebuilt several Q-Jets. I think all of them were on Oldsmobiles. I rebuilt the Q-Jet on my 75 Olds and it was a total disaster. Maybe it is my age (75 at the time). I found out there were a number of changes in the Q-Jet in 1975. It is not one of the best carbs they ever built. I would up sending to a guy in San Antonio that was referred to me and he got it right on the money. For the most part if you watch the videos and read the instructions, they are not that difficult.
I get the impression from the Qjet experts that your era Qjet is an excellent design and shouldn't be too difficult to rebuild. The things people complain about on Qjet's were mostly dealt with by 1974. The big ones being the sheet metal plugs within the body of the carb. Your vintage Qjet has much more reliable plugs from the factory and do not leak very often. Hopefully you have an unmolested one that is correct for the car.
I believe one of the other big items was the fuel inlet fitting. The thread design was changed to a much sturdier design that didn't strip out the threads nearly as easily (although it could still be done if you reefed on it without using two wrenches). If it strips, the only acceptable repair is a large heli-coil. Not the end of the world but a little bit tricky and a little pricey.
So the big things to watch out for is as follows:
1. The fuel inlet fitting
2. Vacuum leaks at the electric choke housing,
3. Vacuum leaks at the primary blades shaft
4. Don't bend the arms of the power piston where the primary rods go.
Did I miss anything fellers?
Post the PN of your Qjet. We can get you lots of reference info if you need it. Pictures would be helpful too!
I’m another one of those “had to teach myself” guys.
What wears in these carbs, as noted (& not) are
1) Well plugs - these get a bad rap. This is solveable. But if they leak, your carb won’t work right. If they leak, your engine will run rich as the well plugs leak gas into the intake which is not supposed to be there. Unmetered additional fuel.
2) Primary blade shaft vacuum leak. This is solveable, but you’ll have to shim the shaft to eliminate the vacuum leak. Test for this by shooting Berryman’s B12 chemtool at the shafts and listening for an RPM rise. If it rises, or changes, you have a leak. You’ll have to drill (very, very straightly), install bushings, then reinstall the primary shaft. I’ve never been good at this. Consider using a professional.
After that, you may have a misbehaving choke, bogging secondaries, and other stuff people give the qjet sh*t for. Across millions of vehicles with many thousands of differing displacements, the fact is that the qjet works well ——If it’s tuned —-. If not, you get all this garbage about quadrabog & qaudraslop, etc.
What these people are really admitting is that they don’t understand how it works. Therefore it’s bad.
That’s wrong.
GM had so many displacements & designs to fuel they built a carb that could work on d*mn near any engine. But it will not work well if you take one jetted for a Cadillac 472 cu.in. & slap it on a Chevy 236 straight 6. Or vice versa.
Many restorers, just slap on one that’s “close enough” and when it isn’t, “the carb is bad”. When, in fact, they just haven’t spent the time to tune it.
The short version of the qjet is is that it’s a d*mn good design. But it evolved from 1965 to roughly 1985. When released, GM realized that they could improve fuel economy by having small primaries where street drivers spend 90% of their time, and big secondaries when drivers want power. Only _some_ drivers nail the throttle a lot, so most customer were happy.
Around 66-72, emissions got more tightly regulated. So GM had to work under tighter constraints. GM reacted by tuning the fuel mixtures leaner & hotter. Engines ran hotter too. Until fuel injection, the qjet worked o.k., or maybe very well, under these new requirements. What’s cool is that the emissions stuff came in after the initial design and it was good enough to work up to 20 years or more with few modifications to the basic design. I’m no engineer, but that’s amazing to me.
The competing Holley square bore (same size primary & secondaries) didn’t meet the new emissions requirements, so it was used mostly in racing and off-road, where it did very well. I tried a Holley 780CFM vacuum secondary in the 80’s and got a tick more power, but cr*ppy gas mileage, so I ultimately returned to the qjet. Holley’s are great if you want pure power, don’t mind gas prices, & like simplicity. I’d use it again, but at this point I know more about qjets.
It’s a little like the MacOS vs Windows debate/war. Undnearth both operating systems using binary language to tell hardware what to do. But as users get more experience with one OS or the other, they get religious about what they think is “best”. Probably because they understand it, not because it’s better. I saw the same effect in business with statistical programming languages: what you know becomes the best _because_ you know it…
This is getting a little dull. But here are my cliff notes:
1) Use a 170- series (75&up) 800 CFM qjet. They’re safer & more CFM than the early designs. And more tuneable. By ‘75, GM had tons of experience with these things in the field. Not only can the later ones meet emissions requirements, but they can also produce more power than the early ones by virtue of slightly bigger (but significant) primary & seconary bores.
2) Build a tuning box which contains all the jets, rods, gaskets, springs and whatever you need to make them work as you’d like.
3) The center fuel inlet models are a welcome safety change as compared to earlier side-inlet. To me, this is as big as front disc vs. front drum.
So i just checked the carb and it has #7043250 stamped on. Now the question is, can i have an idea of the condition of the carb by opening the choke plates and looking in? Honestly it doesn’t seem so bad for a car that has been sitting close to 30 years. According to my uncle, he and my grandfather who was a GM mechanic rebuilt the engine and carb but didn’t drive it due to paperwork problems. I know I’m probably gonna need to replace gaskets and seals but I would have a clearer view on the engine condition too by knowing if the carb is clean.
To specifically answer your question "...is the carburetor clean..."? Based solely on your images, the answer is no - the carburetor is not clean. Don't base engine condition on carburetor condition - they're two entirely different beasts. The carburetor needs a good cleaning and a rebuild. Rubber, nylon, gaskets, the accelerator pump, the fuel inlet spring, fuel filter, etc. all need replacement and come w/ the rebuild kit. I've already provided recommendations on cleaning. That carburetor needs a good cleaning. Additionally, you need to spray the linkages thoroughly and basically follow (once again) the recommendations I already provided.
From 1974 Olds Chassis Service Manual. If you don't have one yet it should be your next order of business. The CSM covers a complete teardown, assembly and adjustments on your QuadraJet. Along with about any other service procedures your 442 is likely to need.
Going by this, if it's a 350 car sounds like it still has its original carb.
Last edited by rocketraider; Nov 2, 2023 at 01:50 PM.
BTW, if you want to gain a general overall warm & fuzzy regarding the basic health of the engine after having sat for 30 years, run a simple compression test on the engine. It does not need to be running. You just need to crank the engine several revolutions. Depending on the environment (in particular) it's a solid recommendation to gain an insight on the compression of the engine. Perform both a dry and a wet compression test of each cylinder. It's a simple process and you'll gain some good insight. Here's a link to a basic compression test. You can often rent or borrow a compression gauge from a auto store. If not, they're not too expensive. You'll learn a lot doing this test in particular: could there be wearing of the piston rings, possibility of valves not seating. If your numbers are good, you'll feel confident the basic health of the engine is good.
With just a little research, you can find out how to evaluate the compression readings. If you have questions, just ask. You can hopefully expect to achieve a compression ratio somewhere between 125psi to 150psi for all cylinders.
Make a simple chart. This is my 350 cid (1971) engine in a 1971 Cutlass Supreme.
There are tons of videos on performing a compression test, here's one:
This is the video i was referring to, do you know how similar it would be to a 1974 442 carburetor?
The 1979 carb has a couple of emissions tuning pieces the 74 carb doesn't. You can ignore the video's sections on the APT jet and the secondary choke pull-off vacuum break; not used in 1974.
Ensure the rebuild kit you order comes w/ a new accelerator pump; if not, ensure you replace the accelerator pump for smooth consistent fuel delivery. Older accelerator pumps don't hold up well to today's alcohol/ethanol fuel blends. The rubber cup on yours is most likely cracked & torn in addition to the springs having collapsed. Below, a review of your accelerator pump & a daily driver rebuild.
Your carburetor accelerator pump Off the shelf carburetor (reconditioned) Daily Driver (rebuild kit) New Accelerator Pump
Ensure the rebuild kit you order comes w/ a new accelerator pump; if not, ensure you replace the accelerator pump for smooth consistent fuel delivery. Older accelerator pumps don't hold up well to today's alcohol/ethanol fuel blends. The rubber cup on yours is most likely cracked & torn in addition to the springs having collapsed. Below, a review of your accelerator pump & a daily driver rebuild.
Your carburetor accelerator pump Off the shelf carburetor (reconditioned) Daily Driver (rebuild kit) New Accelerator Pump
Thank you for your help, your knowledge is appreciated.
Last edited by Andrew Anatian; Nov 2, 2023 at 06:33 PM.
but I will say there are some limitations of DIY. Good rebuilders can get nasty *** chemicals and also have ultrasonic cleaners.. I send mine out because California has too many restrictions to really get good chemicals to get the carb passages clean..
