We have a '67 Caddy Deville with the 429 and a Rochester Q-jet. The car was occasionally floating out a idle. Taping the gas would clean it out. We pulled it apart, cleaned it and rebuilt it. Now we can't even get the car to idle. We have to constantly give it gas. When the car dies you can here what I think is gas dumping into the intake and vapor comes billowing out of the carb. We notice that the brass needle seat in the rebuild kit came with longer threads and that the threads in the carb look terrible. It almost looks like the original brass seat was JB welded in. Are these threads failing common the Q-jet? You'll have to excuse me...I'm a chrysler guy.
the big problem with q-jets is the plugs under the metering rods, they leak. i know of people who have used all seal fuel tank glue to stop the leak. its been a while as i usually just put a 650 spread bore holley in their place .good luck
give my carb guy a call , he is reasonable on prices and is a f'in wizzard with quadrajets Dean Oliver 870 8305470
I've got a Holley Quadrajet replacement carb (spread bore w/large secondaries) that I bought new and ran only one summer before I did an engine swap to a FI motor and didn't need it any more. The carb has less than 500 miles on it and ran like a charm. It cost $375 at Summit Racing new. It's yours for $250 plus shipping if you want to go this route. PM me, email me at cbillelder@comcast.net, or call me at 970-330-6958 Bill
the tops of Q-Jets also warp because people crank those two long front bolts down too hard. the gasket wont seal right in the idle circuit and main nozzle area.
the early q-jets (up tp about '68) had freeze plug like plugs on the bottom of the main casting. They almost always leak, put some soapy water on them and spray air into the main jet holes. The best way to fix these are to tap the plug holes and make some threaded plugs. Also make sure to check the top and center bodies for warpage. These are the best carbs for street use and can be modified for performance too.
You can just put JB weld on the plugs and that will stop any gas from leaking through them. At one time most auto parts carried a repair kit for the stripped threads on Qjets. It was a new fuel nut that was self-tapping.
The seat threads are very rarely messed up. It can happen if a carb has set for a long time dry, the two metals can corrode and pull threads when removing the old seat. Just take a tap and clean out whats there and start again. It could be that the threads are indeed messed and epoxy was the only to save the carb. For the needle and seat to work, the float pivot pin must be held down by the top when assembled. You bend the pin apart so hits the top if the seat is lower then it should be. Just check the top gasket for a dimple where the pin hit, bend it some if you can't tell for sure. Double check the float if its brass to be sure it doesn't have a hole in it, the black plastic ones seldom go bad. It doesn't hurt performance much to lower the float a 32's or so, GM set some of them really high. A really good fuel pump can over power a float slightly, and if its set high to start with, it doesn't take much more to flood a engine. 4psi is all one needs to run good. The leaking fuel wells on the secondary's can not leak fast enough to flood a engine. They leak over night draining the float bowl causing a long crank start each morning. JB Weld is good for this also. Did you clean the vent holes and tubes really well? Thats the down fall of Q-jets, they like to be clean. Once clean, you won't find a better carb for milage and performance. Joe
>the plastic floats do sink replace it<was very common[i;m old enought to have worked on qj's check the float squezze it with your finger nail for gas/the float is a foam stuff with a plastic coating that the gas eats thru they [real parts guys] gave you a float with each rebuild kit
Some good advice already, I agree the composite floats quite commonly get heavy. Unless it was urgent and one was not available, I always replaced the float when rebuilding.
This was our initial thought. When we pulled the carb apart the float was 1/2" from the top of the casting and the instructions said to adjust it so that it is 3/16" from the top of the casting. This makes it parallel to the surface. So we adjusted the float. The float is not leaking or sinking. We adjusted it back to the 1/2" it was at before and it still floods out. Bad. It runs down right awful. Even when giving it gas it kills itself eventually. We're going to have to change the oil after this one. I appreciate the advise. I honestly didn't think JB weld would hold up against fuel that well. I think what we'll do is JB weld the brass seat into the threads and see if that helps.. yuck! I don't think retaping it would fix anything. And a helicoil would probably just make it worse. As for the plugs leaking: I've read a bit about this. It was having some long start issues before. The rebuild kit cam with a piece of foam to put under the the plugs as though it is suppose to help. Should I put some JB weld on the bottom of those plugs to be sure?
you can put jb weld on them but check them with air and soap after they're dry. If it's the freeze plug style, I would just o straight to the tapping the hole. If it's the lead plug then you can try jb weld. The foam piece will get soaked and leak past it. I would double check everything, make sure there's no vacuum leaks, make sure the primary piston is ok and all check balls are in. also this is a great book for info. http://www.amazon.com/gp/product/1932494189/ref=pd_lpo_k2_dp_sr_1/177-2976325-5105504?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=lpo-top-stripe-1&pf_rd_r=1Z1HPR3WZA9C8MQ05QR1&pf_rd_t=201&pf_rd_p=486539851&pf_rd_i=0895863014
Is the Q-Jet correct (by identification number) for the engine, and did you acquire the correct rebuilding kit? One of the most common causes of seeing the vapor after you shut off the engine, is using a carburetor/gasket/manifold combination that do not match. As to the carburetor fuel valve seat, MANY different, not-interchangable designs were used. However, the use of expoxy to hold in a valve seat is not recommended. As stated by others, the 1965~1967 bowl-style lower plugs do leak. An aftermarket threaded replacement is nice, but BE CAREFUL!!!!! The casting cylinder holding the plug is quite thin. We have received for rebuilding a number of castings where enthusiasts tried to thread the casting and split it instead. 1968 was a transition year; with some castings receiving the bowl-style plugs; but most using a different, thicker casting that was spun OVER a flat plug. We have not seen leakage from this style plug. And the book pictured above by Cliff Ruggles is an excellent investment for anyone even considering rebuilding a Q-Jet. While Cliff is a friend, and the following might be taken with a grain of salt; this book is the most "user-friendly" of any carb book I have read in the last 50 plus years. Jon.
I gave up pissing around with Q-Jets about 10 years ago. I have a local carb shop that is very good and reasonable. I also have a Holley Q-Jet that I move around from car to car, works like a champ all the time. Bob
please don't ditch it... i am a Chrysler guy too but, Q-Jets when set up right are an awesome carb, the problem with Q jets is mostly the people working on them, there a pain to set right to say the least, do what i do with them, send em to someone who knows them inside and out.. you wont be disappointed...
The two bigest problems with Qjets are screwdrivers and pliers in the hands of assholes who think they know how to adjust them. Also the composit floats are easy to check out. They don't fill with gasoline like brass ones with a hole. Put the float in a small pan of gas that is about 1/4 inch,put the float in it and let it sit for 10-20 mins. If the float is bad the gas will go up the sides of the float and sit on the top,which would make the float sink if it was in the carb.
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