Hello all! I have a q-jet off a 74 LeSabre I am thinking of rebuilding for the experience. I've heard that it is not too bad of a job for someone of limited mechanical experience (such as myself). From what I have gathered in reading, basically what you do is take everything apart, clean it, and put it all back together. Is that all there is, or is there more to it than that? Thanks for the advice. - Freed
carb kit If it were going on a car, then I would get a carb kit and new float from NAPA or carquest. That costs about $30, but if you are just doing it to learn and don't plan on usuing it, your plan should work. The carb kit has everything in their to rebuild a carb from gaskets to springs. It does not have a float though. I think a little secret it to bend the float up a little to keep more gas in it, for quick slams of the throttle. The carb kits also has directions, but they can be overwhelming. (I know its just a carb - how complicated could it be) But you'll see what I mean when you look at them. Especially if it is your first time. But say you got good at it, guys pay alot of money to have somebody rebuild their q jets. My first q jet I paid $100 bucks to have done, and it worked real well though so I didn't mind. A buddy of mine pays a guy $200 bucks every couple of years to freshen his q jet up. There is a magazine article that must be around 30 years old, and it shows you how to get almost 30 HP more from a stock q jet. The write up was done on a carberated corvette, so It must be pretty old. Maybe somebody on this board knows what I am talking about. That would be good info to look at. Good luck!
Me too Me Too Freed: I am in the same boat. Bought a '73 750 off E-bay for 12 bucks. I've been reading a book dedicated to Q-Jets which includes function, rebuild steps, and performance mods. It is a black, thin, soft cover book available at Borders and B&N. Lots of pictures.
Q jets have a bad rap, IMO, from folks who rebuild them wrong. Not saying you're gonna do it too, I'm just saying that yes, they are a bit complex, but not exactly rocket science. The only Rochester I bothered to rebuild myself was on a Regal, so it doesn't apply, but I will say the instructions that come with the rebuild kit should be called "vacuum instructions"...because they SUCK. I will cast a second vote for getting a book on Q jets. Personally I find a manual or book that gives instructions plus multiple diagrams PLUS theory of operation turns the "Step one, step two" process into something I understand as the rebuild progresses, rather than what happens when I use the instructions that come with something like a rebuild kit- even if it works when I'm done, I don't really know what just happened. I like to know why it happens- handy when something doesn't work, because you know where to start troubleshooting.
Make sure you know exactly where every part goes and how it was positioned...such as the linkage for the choke and butterflies. If you put one of those in backwards you'll screw it up and have to take it back apart. Be careful with the metering rods...they're fragile. Find a good carb cleaner such as Gunk in the gallon cans or some berryman B12 chemtool in the spray can. Buy some carb and choke cleaner so you can spray the jets and all the little crevices out before you slap it back together. The float... I tried leaving the float bent up so that there will be more gas in the body, but when I ran it the first time, gas spewed out the gasket in between the air horn and carb body. So I took it back apart...cursing all the way...and bent the float where it is SUPPOSED to be...for mine it was 3/8 in from the top of the casting. That solved my problem. Now I am still playing with the secondary butterflies to get the right spring tension for the air valve. Still have a slight bog when I jam the throttle at about 40mph. Let us know if you have any questions regarding the rebuild.
Q-jets only seem complicated because there are probably twice as many parts (and even more if its an emissions carb). But you can make them run very well with a few mods. I'll agree that you'll need a good carb kit (never used napa before though) and a gallon can of Gunk carb cleaner. An air compressor is nice to have, also. I suggest that you get the book Rochester Carburetors by Doug Roe published by HP Books. This is an excellent read. It gives a little history, gives you pictures of the different rochesters and, most importantly, it gives instructions on how to get a little extra from your carb. Q-jet parts are reletively easy to find if you know where to look. Edelbrok sells rods, primaries and a couple of other doodads. If you have part #'s you can go to your local GM dealer and possibly get parts (never done it myself) It would be a good idea to go to the junkyard and get a few extra carbs. I'm not sure if the 74 is an emissions carb or not. I usually stick with the ones with a divorced choke. I like the Pontiac ones since the 800 cfm Buicks are so hard to find. These will have pull over enrichment tubes for the primaries. Originally they were for emissions, but can be modified for a good top end charge. Good luck!!
75 started the emissions fiasco with the 800's. I have a 76 that runs very well on my 350. I really can't tell too much difference in the way the carbs work...little things I suppose. I always have fun playing with toxic chemicals though!:TU:
The Q-Jet is to carbs what Buick is to Performance. Under-researched, unknown, and a real killer on the street in the right hands. Chris is right on, they have a really bad rap when not done right, and not tuned afterwards. A Qjet may not be the king at raceday, but nothing drives as smooth as a well done Q. Some simple mods and it'll hit like fuel injection, pull into the secondaries like a holley, and idle with your evil camshaft in there. Definitely pick up the Doug Roe book if you plan on doing any performance tweaks. Some learned tips not in the book: For tools, add a numbered drillset to your collection. For $10 I was able to drill out idle restrictions, secondary well tubes, and upper pump shot ports. A good rebuild kit comes with spare gaskets to let you rip into it twice. Removing the top takes about 5 minutes after the first few tries. Head down to the local wrecker and strip down a few Q-jets for practice. Take out the jets, primary rods, secondary rods, and hangars for your collection. You'll get charged 1$ for all the "junk" and learn how to strip the Q without hurting it... I've run 71 and 76 Q-jets, same jet & metering area, on the same car with.... no difference! Buicks had a phenolic delete for the 75-76 carbs that eliminated the altitude adjustment, which means its identical to the 71... Float level and Inlet size go hand-in hand, if you increase the inlet you'll have to lower the float. Otherwise it'll spew, stall, and die. If you get a bog on acceleration you might be lean OR rich! Idle and primary acceleration are closely linked (same metering) so... if idle improves after cupping your hand over the choke your jet/rod combo is lean. Hope that helps!
Clint, Good info there...appreciate it! I just spent the morning under the hood in 10* weather trying to figure out why my electric choke isn't working. I think I reinstalled one of the parts backwards. I'll figure it out eventually.
Joe and Clint are right, that Doug Roe book is something else. I bought the book before I rebuilt the carb on my old GS455. I never did get it tuned right (actually I had it tuned real well, I never got the choke working properly). I was running an edelbrock carb on it, and the difference between the primaries and secondaries on the edelbrock is not nearly the difference of the Qjet. When I got the Qjet tuned right the car pulled like a freight train. I think I may follow Clint's advice, and make a run to the yard to pick up some misc Qjets to rebuild, and strip a few of the parts....
I think most of the yards around here have been ravaged of all the good QJets...I got mine from one and it was the last decent one there. I'm still having trouble with my choke. It doesn't seem to want to close the primary butterfly when it engages. I wish someone who knew all about it could look at it. When it's cold, it die 4 or 5 times before I can get it to stay running. Then I can sit there with my foot on the pedal for a couple minutes to warm it up. All the linkages are connected...there's one thing I'm not sure about, though. There's a bracket that is behind the choke housing that stops the secondary throttle blades from opening. Can I remove it without problems? I think that is what is causing my problem. The parts are getting tangled and the choke can't close the primary butterfly. I might have that secondary stop bracket on backwards. It's a huge pain in the butt to remove it though.
So this brings up the obvious question... What are the good Q-Jets to get from the boneyard? What cars have them? - Freed
Look for QJets with model numbers beginning with 704xxxx. It's more complicated than that, but do a search on this site for 800cfm quadrajet...there are a couple lists of card model numbers listed by some of the members. Also, in there are some good pointers for searching the yards for good carbs.
If I could figure out how to use this damn digital camera I'd show you a picture of the ones I like. As I said earlier I like the Pontiac carbs. They will have rectangle shaped slots in the secondary butterflies (upper), and will have extra metal on the air horn in the primaries for the pull over enrichment tubes (there is a picture of this in the Doug Roe book). Most of the carbs with the number 70xxxxx will have a divorced choke, not the round shaped thing with the plastic cover. In a junkyard that I frequent, I usually find the carbs in school buses and old pole buildings (it used to be a farm, and it still has cattle that chase you around). The ones that I like to get are covered in oil or are greasy. These have a better likelyhood of coming apart without breaking things. I try to get the most complete ones. About 90% of the carbs you'll find (or at least in my experience) will be 750's. This is pretty much why I've given up in trying to locate 800's. I'm sure the 800's came on something other than Buick BB's. Can't imagine the Cadillacs not having one. In another carb post I was involved in I think Kerry posted a link to a pic of a 750 and a 800. It shows the primaries and there is a pretty noticable difference. Happy hunting!!!
Here's the link to the other post ://www.v8buick.com/showthread.php?s=&threadid=10816&highlight=carbally Actually, Clint posted the link to the carb picture. I clicked on it, but apparently my browser can't find it. Kerry posted a link to another thread.
OK I screwed up. How do I make that link clickable? Do I need to put it in the attach file or somewhere else to make it work?
Make sure to get some epoxy or JB-Weld to put on the bottom of the metering well plugs! They have a nasty habit of leaking.ou: If you have a tough time getting your car to start in the morning or after sitting for several hours - that could be one of the culprits. Also, before you buy a carb out of the junkyard or elsewhere, move the throttle blades back and forth - you want to see if the throttle bushings are OK or shot (real sloppy). I would also recommend the book by Doug Roe (mentioned above) - very detailed, with alot of pictures!:TU: Always make sure to run some wire thru all the passageways and blow it out with compressed air when available. At the very least, use the red spray nozzle to get into those passageways and make sure you see the cleaner coming out the other end. Don't forget the goggles!!!:Smarty: Your eyes will thank you!:TU: If you're unfamiliar with the Q-jets, make sure to write down or otherwise mark, which hole you took the linkage out of - sometimes, there are more than one hole there. You'd better make a note which end of the rod went where also! It helps to have a small punch on hand, to get the tiny roll pin out of the accelerator pump linkage on the top. Your rebuild kit should have a new one (make sure first - so you know whether to save the old one). On re-assembly - don't overtighten the screws!!! Not only can you easily strip the threads - you run the risk of warping that soft aluminum!! Make sure you have a large CLEAN bench or table available to lay everything out on! Keeps the job well organized! You can keep all the parts layed out in sections, as to where they came off. Don't forget where the small one way check balls came out of...and go back into!! Take your time and follow the book! They're really not that bad!!:TU:
i think the 800's had it Didnt the 800cfm Q jets have 2 rings, one on top that is obvious, and then another down in the bottom of the back barrels, That denotes it from other 750's. Some one want to refresh my memory. Thanks
The 800's have a noticeable bulge in the primary venturi that the 750's do not. The bulge was breathing room for passageways that were routed so they were slightly "in the way" of the venturi so it was bulged.
Adam, You can indeed grind, pull, cut, or swear at that tab until your air valve opens to 85*. One of the ways GM made the Q-jet universal for smaller engines was to limit the air valve. Your Q can be opened all the way, but don't exceed 90* or you'll mess upthe airflow. Hmmm... that link seems to have gone down. I'll try and find a link. The bulges are on the outboard rear quarter of the primary venturi's.
