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Thread: Quadrajet

  1. #1
    Senior Member RACING JUNKIE
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    Quadrajet

    Starting resto on 327/motor in my Chevelle... trying to keep it bone-stock looking. I noticed it had a older Holley econo PUKE MASTER carb someone put on it back in the day... original Q J carb is long gone.

    It looks like I can get the correct QJ original carb pretty easily. I know NOTHING about them... nothing. Do I just buy the one that the car originally had, or should I get a little different one that might perform better? Remanufactured okay? Motor will be stock except for mild cam, stock pistons, w/ Edlebrock int, etc... I want everything to look bone stock when the hood is opened. Even the Edelbrock intake has been stripped & painted Chev orange. It is not a carb I would seek out, but it is what it came with...

    Are they as complicated as they look?
    "I would walk through hell on Sunday before I fear the enemy"

  2. #2
    Senior Member DYNO OPERATOR
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    Quadrajet

    Quadrajunk, Quadrareject, are names people used to call them back in the day. They were maliagned for their many problems. I have rebuilt a blue million of them, and I liked every one of them. Also ran few in class racing.

    Get the exact same Rochester number as listed. It will have the proper throttle linkage, choke style, and jetting. Most Chevys had the same linkage, but there are 3 choke styles and many jetting combinations.

    The primary side has replaceble jets and metering rods. The secondary has fixed orifices and replaceable rods with a lettered hanger for fine adjustments.

    Numbers were like 7029203

    702 is the series, also 705, 708, 1705, 1708

    9 is the year 1969

    203 is the number for the exact engine combination. This is the one that will get you the right fuel metering set up for your stock engine.

    They are easy to rebuild once you see someone else do it. I have seen lots of bent metering rods on ones 1st timers tryed.

  3. #3
    Senior Member RACING JUNKIE
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    Thanks Mark!! Way to break it down! That helps. I will proceed w/ the correct one w/ divorced choke.

    Is there are way to minimize the slight stumble from the secondaries kicking in or is just because they are so big??? Can any mod be done kick them in more smoothly?
    "I would walk through hell on Sunday before I fear the enemy"

  4. #4
    Senior Member MASTER BUILDER
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    Rigsby,The air valve on the top of the secondaries that looks like a choke plate has a small adjustable spring.Tightening that spring will slow the opening and fix that,most times.A small adj at a time is best.Bill.

  5. #5
    Senior Member DYNO OPERATOR
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    quadrajet

    The air valve shaft has a screw on the passenger side. Hold it with a small screwdriver and loosen the vertical allen set screw under it. Like said, only tighten spring 1/16 of a turn at a time. Not more than 1 1/2 turns total tension or the spring will stretch. You might want to mark its original position in case it slips. With the car running at idle, if you open throttle quickly, momentarily, the air valve should just barely tip in.

    Also the choke pull off diaphram has an orifice in the end that attaches to the vac hose. There were several different size orifices originally. Or you can measure the hole with a number drill bit, epoxy it shut and then redrill it a smaller size. The smaller the hole, the longer delay till opening. .026" was a commom orifice size.

  6. #6
    Senior Member RACING JUNKIE
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    scooter mark is dead on.take his advise.i use to run qjets back in the day. i was one of very few who really like them. one you have them dialed in i believe you couldnt beat them. track or street.with my holleys i was always dialing them in for different conditions.but with my qjets once i had them they seem to stay. never had to dial them in at the track even after runnin them on the street.and my times seem to stay consistent.once you build one they are really easy to build. atleast for me.

  7. #7
    Senior Member RACING JUNKIE
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    Gentlemen thanks. I have printed this thread & I am going to do exactly as you said. I have always FEARED the Q-Jets.... only worked on 4150 Holley style carbs mostly. I am trying to keep everything on this car as "1968" as possible... even going to keep the points dist (I think) & still run stock exhaust manifolds... so it looks bone stock under the hood. This is my first virgin/bone stock Chevelle... all the others were whores.
    "I would walk through hell on Sunday before I fear the enemy"


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