I have a 70 GS Stage 1 that has been sitting with very little running time for over 20 years. There is a lot of crud built up on the outside of the carb and I'm guessing junk inside too. It seems to work okay, with the exception of the idle going up and down a bit until it warms up, but nothing major, I just have to hit the pedal and the idle drops back to normal. I've seen the big cans of carb cleaner that you can buy, would it do much good to soak the whole carb in that stuff? I'm mainly wanting to get rid of any junk that might be built up inside. Once the fall rolls around I'm thinking of rebuilding the carb or having it done, just to make sure that there won't be any issues next spring, and was wondering how hard is it to install a rebuild kit? I saw a printout of the carb, in exploded views, and it looks a bit intimidating. I don't need any mods, just to be reliable. Thanks, Scott
This issue sounds to me like the choke coil is not heating up correctly. The result is that the air flow around the coil is cooling it enough to partially close the choke. make sure that the heated air cleaner is working; this heated air is necessary for the choke to heat properly. You might also check that the vacuum passage in the choke housing is open; you should feel a slight vacuum on the large opening at the bottom of the housing. If you don't before condemning the vacuum opening, make sure that the choke housing seal on the choke cover is ok. Two points to check. Ray
Unless you are having problems with this carb, 90% of the time, repairs can be made without a rebuild. Rebuilding can be tedious; I do not recommend this for the faint of heart. If problems ensue, you should know how to troubleshoot this carb to find the problem, without undue damage to the carb. Ray
I agree with Ray, Check out the choke, linkages, etc, to see what's sticking. Spray Carb cleaner can work wonders, just keep it away from plastic and rubber (and paint). If/when you rebuild: It isn't that big a deal, if you TAKE YOUR TIME, and pay close attention to how it comes apart. Cleanliness IS Godliness with carbs. I like to spread out a sheet of butcher paper or something, and lay the parts out in order, like they came off, makes it easier to re-assemble. Q-jets are fairly simple, once you get past all the linkages, and keep track of which way they go. The cans of carb dip cleaner are great, but I usually end up using a spray can of B-12, compressed air is also a great thing to have for blowing out passages, etc. You ought to be able to get a rebuild kit for under $20.00 at your local parts house. Take your time, and have fun!
isnt a 70 a divorced style choke with no vacuum passages in the choke mechanism? seems to me that the 70 choke coil is located inside a cavity in the intake manifold and has a sheet metal cover over it. i could be wrong but i highly doubt that the heated air off the exhaust manifold has anything to do with choke function. it simply allows the engine warmer air to aid in fuel atomization and prevent puddling in the intake on very cold startups.
Yes, that is how mine is. The choke seems to be working okay, I think one of the issues is a vacuum leak somewhere along the way. I'm redoing the vacuum hoses and got a diagram last week, so once I get everything back to the way it should be, I'll see if that helps with the irratic idle. The idle isn't real bad either, just enough that I can hear it. It idles high after a few minutes, until I hit the gas pedal, then it slows down to normal. The main thing is, the carb looks horrible from all of the sitting and dirt accumpulation. I figure, if it has that much crud on the outside, the inside probably isn't much better. These may be things that I have just never seen before and may be normal. This is my first muscle car, so I'm not sure about a whole lot of things. Scott
Quadrajet Rebuild The Quadrajet is the one of the easiest carburetors to rebuild. There are only two main problems with them, one the bowl wells leaking and top vent warpage. I have a source for the thicker top gaskets for the second problem, AL.
I don't have any real experience with the q-jet. My GS has a spreadbore Holley on it that was on the car when I purchased the it. I will also have to rebuild the Q-Jet someday as I wish to get it back to original equipment. I would not recommend any so called carb cleaners that are added to the fuel tank if the Q-Jet has neoprene floats. I did this and I suspect I ruined the neoprene float in the Holley - I soon had to rebuild and replace the float because it swelled and absorbed gas making it heavy and the result was flooding the bowl. The mechanic that did the rebuild suggested that the float was bad due to gas additives. I have not added any such additives since and I have not had any problems since the rebuild that was probably over 10 years ago.
Quadrajet Rebuild Sorry Adam, if you need a good source on "Q- jet" parts contact Bob Stone at ClassicCarb@aol.com , or PO Box 212 Line Lexington, PA 18932 or carbdoctor.com , this guy is the best on these carburetors and his handle is Carb Doctor on some sites, AL.
My apologies, guys. The seventies were a mutable decade, with changes coming fast and furious. Though the execution may use a divorced choke, the problems with the choke coil are the same. If the coil fails to fully heat, the result can be a coil that partially closes the choke after a long run in cool temps. Typically, these problems were fixed by the coil mounted on the housing, and the thermal air cleaner. This was done in the emissions era as a necessity to control emissions. Ray
Where did you get a vacuum diagram? I have been looking all over. Is there any way you can post it or e-mail it to me? I am sure a lot of people would be happy to find it.
I need the vacuum diagram for a 1975 Buick Lesabre with a 455 going to a rochester Q-Jet 4B. I am not sure all the vacuum lines are hooked up right as the secondaries fail to open. Also if any one knows why they would not be opening and have advice, I would love to hear it. Thanks.
If your carb is dirty on the outside, and you want to clean it, spray it with aerosal B-12. The Berryman carb cleaner in the bucket is good, but the carb need to be dissasembled to be soaked. Kyle, your holley spreadbore is probably only 650cfm, so you need to get your Qjet back on and get back to 750cfm. Your Buick will love you for it.
another thing that can cause surging is a pin hole in the vacume diaphragm of the vacume advance in the distributer....this would ad vance and retard the timing over and over.....:Brow:
I'm not sure how familiar you are with the Q-jet. The secondary throttle blades open mechanically. The secondary air valves are located on top on the secondary portion of the carb. If you open the air valves by hand and then open the throttle all the way, you can verify that the secondary throttle blades open all the way. The air valves open as a result of the low pressure area created when the secondary throttle blades open. The air valves will not open if you wing the throttle with the air cleaner off. A lot of guys mistake the air valves for the secondaries. They expect to see the air valves flap open if they rev the engine in neutral. The air valves size the carburetor air delivery to engine demand. They open in response to engine demand. There are 2 control mechanisms for the air valves. The first is that they are spring loaded. The second is that there is a link from the primary vacuum choke break on the passenger side front of the carb. Those 2 controls slow the air valve opening. If the air valves open too quickley, you get the Q-jet Bog. If you tip in the air valves with your finger, with the engine off, they should snap back closed when you remove your finger. You should not be able to open the air valves with the engine running. The vacuum break should hold them closed. The vacuum lines under the hood really don't have much to do with secondary opening except for the the choke break mentioned above. Most of those vacuum lines are unnecessary except for emission control. You can remove them and simply run a line from the carb to the distributor vacuum advance. There are other full vacuum lines that operate the climate control doors and the air cleaner. The best source of vacuum diagrams are the Buick Chassis manuals. Here's one on E-bay: http://cgi.ebay.com/ebaymotors/_Man...arms=39:1|65:1|240:1318&_trksid=p4506.c0.m245
Larry's got it...that post should be a sticky. As Larry described, the Q-jet is actually a variable venturi carb. The secondary air valves regulate cfm's due to demand. They also create the venturi effect over the fuel inlet pipes, as opposed to the primaries that have a fixed veturi. The shape of the carb body(secondary barrels) helps create this venturi effect.
Well thanks for all your help, I actually had the vacuum lines hooked up correctly and plan on taking a bunch of pics for everyone else here. I took the car to my father in law's and he explained it all to me. The primary choke on the passenger front of the carb held the secondaries closed and we had to adjust to open the front barrels 5 degrees. When the vacuum drops off and you punch the accelerator (even with the air cleaner off) the secondary barrels open and God's vengence is upon us! But then the vacuum rises again and the lock goes back on those secondaries and you have to wait until the vacuum drops again to punch it. It was tricky to understand but after my father in law showing me what to do, we did a few burn-outs and it was great! Well hope that helps a few people and I will get those vacuum line pics up as soon as the next time I have the air cleaner off again, which I will give a couple hours if past experience is anything. As soon as it's drivable, it is time to put it away for the winter!
They are pretty easy carbs to take apart if you take your time. Cleaning everything and adding new kit should really help. Of course throttles always need bushings and well plugs epoxied.
