Carb, idle, and dieseling issues
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The Classic Cadillac Forum Discussion, Carb, idle, and dieseling issues in Past Cadillac Vehicle Discussion; My 68 has the quad still on it but I'm thinking about swapping to a edelbrock or holley. With a ...
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    FoxRodder's Avatar
    FoxRodder is offline Cadillac Owners Fanatic
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    Carb, idle, and dieseling issues

    My 68 has the quad still on it but I'm thinking about swapping to a edelbrock or holley. With a couple searches I found people singing the praises of the quadrajet over everything else, and then praises of edelbrock over any quadracrap in existence. I've researched the quad stuff to try and figure it out but its got so many variables to cause problems. I need the thing to run reliably and right now its stalling out when at a light. I can't be stalling out in heavy traffic around this crowded city of maniacs. I was able to get it running solid one day with a somewhat high idle but the next day I drove it, wanted to stall at every stop. Goes down the road just fine otherwise. The higher the idle the worse the dieseling on shutoff.

    I'm considering using an adapter and putting a new carb to eliminate all the variables in the old setup. I don't know how old the carb is, if its the original, how many rebuilds, ethanol damage, modifications etc. I'm a bit worried about the rotary kick down switch and how to hook them up with the mechanical linkage since they are usually used with cable. I'm also curious if there is any other common way to actuate kick down since I don't see a source for replacement switches.

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    cajutila is offline Cadillac Owners Member
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    Re: Carb, idle, and dieseling issues

    I'm a bit of a stickler for staying with the O.E. equipment. I bought the book on Rochester carburetors by Doug Roe and learned a whole new appreciation for the the Quadrajet and how to set it up for use. That and the indispensable Factory Manual which can usually be found for sale online. Between the two, you should be able to sort most of your issues. Of course, this assumes you are not depending on the '68 for current transportation in which case you may find a rebuilt unit form Holley or some other rebuilder. In any case the two books will be a great help.

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    SWEENDOG1969 is offline Cadillac Owners Member
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    Re: Carb, idle, and dieseling issues

    I have had nothing but problems with rebuilt junk from holly. The latest reman carb the car wouldnt even run...just stack fires. was going to go the edelbrock route but the linkage wouldnt work with the kick down for the trans without mods because of the the spacer required to meet the new carb to the old manifold(spreadbore and squarebore).

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    FoxRodder's Avatar
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    Re: Carb, idle, and dieseling issues

    I do have the 68 shop manual which goes into good bit of detail but almost too complicated to understand and work with. I have found posts from other forums with people saying that the rebuilt q-jets have been junk as well. Jet Performance seems to have a good rep for doing them but I still question it. The linkage is still a mystery to me because I can't find any pictures or documentation of people doing it. The kickdown switch would not be a problem one way or the other because its just a matter apparently of sending 12v to that component in the trans. That can be done with the expensive Lokar kit, the cheaper B&M kit, or by some kind of simple temporary on button switch mounted under the gas pedal or its arm.

    I'm still undecided for lack of information. Would anyone happen to know where I could find a proper replacement fuel filter for these? The filter is designed to thread into the metal tubing from the fuel pump and outlet to the carb but also has a return back to the tank. I'm curious where I could get a replacement filter and also a pump that wouldnt require modification. I've heard of problems with older pumps not liking ethanol.

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    FoxRodder's Avatar
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    Re: Carb, idle, and dieseling issues

    Well I just found some extra goodness going on with my qjet. Had engine running and warm and it started stallingat idle. I had the aircleaner off and when the motor stalled out, I saw a fuel fog coming from out of the primaries. I then saw and heard fuel getting dumped out of the boosters. I started it again and watched it do it again for probably 15 seconds after it had stalled. I also found that the fast idle cam had gotten stuck from the last time I tried to drive it and couldnt get the idle down.

    So anyways, now something has to be done but I can't figure out which way to go. My buddy says he has some Holley spreadbore carbs that would need a rebuild. Otherwise its new holley or edelbrock if I could figure out the linkage. My other buddy lent me a used edelbrock 600. I found that summit has a fuel line adapting kit for steel line that comes together with the spreadbore adapter. Options are good, decisions are lame! I could send the qjet off somewhere for a rebuild but they are the same or more cost than a new carb!

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    Jaykeane is offline Cadillac Owners Member
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    Re: Carb, idle, and dieseling issues

    From experience, the engine running on and the stuck fast idle cam are likely related.. if you shut the engine down with the throttle blades open, you'll run on / diesel.. The throttle shafts could also need to be re-bushed to tighten them up..
    When I was a kid, i was a holley nut.. These offered excellent results at the drag strip once they were dialed in.. which took a lot of fiddling to get right (which entailed yanking the carb, popping it apart and changing things like jets, secondary vacuum diaphragm springs, squirt nozzle sizes, power valves and squirt cams.. don't expect perfection out of the box... I have tried the remanufactured q-jet carburetors from holley.. and never had any luck with them.. Edelbrock carburetors are usually pretty good out of the box, but are picky when it comes to fuel pressure.. These are basically Carter AFB carburetors which were OE on dodge Chrysler and plymouth cars of the 60's and 70's.. edelbrock bought the tooling and worked with Webber to offer a more user friendly / more tunable product.. These are fairly well tuned for common engines, 305/350 GM and 302 /351 Ford.. You're 1968 5000 pound car was not on Vic Edelbrock's mind when he thought to make good all around performance carburetor..

    I suggest sticking with the Q-Jet.. Having yours done.. I know of an outfit in New Hampshire (Hobb's Carburetor) who has done a few for me in the past.. this way you won't have any additional gaskets, intake adaptors, cobbled together kickdown and throttle linkage.. and your air cleaner will fit correctly without knocking it with a hammer.. also, your hood will close the first time!
    I do my own Rochester carbs now.. the kits are cheap, like 25-30 bucks..

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    FoxRodder's Avatar
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    Re: Carb, idle, and dieseling issues

    I've come to a decision that reflects what you are saying. I decided I'm staying with the q-jet. I actually had it running properly yesterday for 25 minutes and drove all around the neighborhood with no stalling. After a restart I began to show intermittent stalling/flooding but not as bad. I'm convinced that its related to the float/needle area and possibly to do with gunk or dirt. I'm going to play with it some more before I decide to yank it.

    What I did find on cadillacowners forums, was a reccomendation for a company called "Mountain Man Fuel Systems." They do their business through ebay if you have a more common model or over the phone to send yours in. They specialize in q-jets and its actually a husband and wife operation. I spoke with the wife about my 68 jet and she was very helpful and very very nice. They do rebuilds for I think 169 which includes rebushing the primary shaft. They have lots of good feedback, so if I pull mine off, thats where its going.

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