'87 Q-Jet Adjustment Question
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5.0 and 5.7 Discussion, '87 Q-Jet Adjustment Question in Cadillac Engine Technical Discussion; Alright, so I've rebuilt and nearly retuned my Q-Jet on my '87 307ci Brougham. Before finishing the tune, I stupidly ...
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    FrankieSixxxgun is offline Cadillac Owners Fanatic
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    '87 Q-Jet Adjustment Question

    Alright, so I've rebuilt and nearly retuned my Q-Jet on my '87 307ci Brougham. Before finishing the tune, I stupidly threw away the sheet on tuning it that came with the rebuild kit. Specifically, I need to know the proper adjustment to make to the car at high RPM to get the fuel mix right. I've done the adjustment with the idle air screw to get the dwell rocking 30 +/- 5 at idle, but I believe there's an adjustment to one of the 2 remaining screws at the top of the carb to get 35 +/- 5 (I think) at 3000 RPM. Anybody know what I'm talking about?

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    FrankieSixxxgun is offline Cadillac Owners Fanatic
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    Re: '87 Q-Jet Adjustment Question

    To answer my own question:


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    Re: '87 Q-Jet Adjustment Question

    I have done full adjustments to mine, but I don't have my book handy.
    .
    I don't remember any adjustments at 3000 rpm other than high idle, which I never allow that high, it is just too much.
    .
    Basically in a nutshell you disconnect the alternator (I think on those cars, but forget for sure, my 91 Cad you did) and adjust for idle to be at 50% dwell at idle. (Center of the spec). You have to do the min adjust then the max, and then the air bleed adj if I remember right (the picture you scanned isn't very readable).
    .
    90% of the time the factory adjustments are still dead on. Don't mess with the idle adj unless you have a very good reason to, I have never been able to get one to actually change from stock settings to be correctly adjusted. Rochester was very good on this adj.

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    FrankieSixxxgun is offline Cadillac Owners Fanatic
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    Re: '87 Q-Jet Adjustment Question

    Whoever had my car before me took it for a, "tune up," and whoever touched the carburetor was a complete and total idiot. Everything is so completely out of whack on the thing that I was almost ready to buy a new one and start over, but a rebuild and putting everything back to stock like the rebuild kit suggested was a big improvement. Right now I have the idle adjusted to rock back and forth at +/- 5 from 30, which is center, on the dwell meter, so it idles like a dream.

    The only problem now is that it starves out at cruise RPM and starts to knock. If I stomp the pedal and hit the accelerator pump it'll stop knocking, but it comes back pretty quick. Same thing happens if I let off the gas and stop delivering air. I'm thinking a quick 1/2-1 turn on the rich stop screw should help. My guess is that the computer just can't adjust rich enough at throttle because the stop screw is rolled too far in.

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    N0DIH's Avatar
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    Re: '87 Q-Jet Adjustment Question

    sounds like you are on the right track. If the rich or lean stops are hosed it will screw it up. Not easy to "watch" on these cars though. You can keep the dwell meter hooked up and bring it in the car and watch it as you drive.

    Make sure the pinging is not due to EGR blockage, which 307's are notorious for. They EGR tube extensions under the carb often get blocked with carbon deep in the intake, and it will ping as you describe.

    As for the rich/lean. There is a tool that you have to insert into the carb to measure the rich stop and then the lean stop, and the distance between. And it is referenced off of the air bleed at the top. It used to be available at parts stores. The carb kit doesn't come with it. I have it, I bought them after I got the car and had to replace the carb because a gorilla tighten the carb down to around 30-40 lb fts. Needless to say when I figured it out I wasn't too pleased. I may have done it (but REALLY doubt it), or it was one of the shops dad took it to to do a water pump or intake manifold years ago. I couldn't adjust TPS. It was crushed.

    I can look for my tool and see if I can copy the dimensions for you. I don't know if it will help much, it had a place to settle down in the carb to make accurate measurements. It was needed. And took a special carb tool to adjust it.

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    FrankieSixxxgun is offline Cadillac Owners Fanatic
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    Re: '87 Q-Jet Adjustment Question

    I found the tools online. The gauges are ~$10 and the toolset is ~$15, so I'll probably just order them. I'd love to get this car running without knock because I really want to sell it and but this '53 Buick Special I saw

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    FrankieSixxxgun is offline Cadillac Owners Fanatic
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    Re: '87 Q-Jet Adjustment Question

    Damn, I got the adjustment tools, but I was unable to get the gauges. Does anybody have a set of gauges or at least the specs that I'm supposed to adjust the stops to? I'm sure I can just use a piece of cardboard that I measure out with a ruler to get the adjustments, but I can't quite make out the measurement on the picture of the manual I downloaded.

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    N0DIH's Avatar
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    Re: '87 Q-Jet Adjustment Question

    Which gauges? The one to set the M/C solenoid stops? It is a bent 1/8" rod with a plastic piece to put it in a calibrated position in the carb. I can take pictures of mine, if that would help.


    Quote Originally Posted by FrankieSixxxgun
    Damn, I got the adjustment tools, but I was unable to get the gauges. Does anybody have a set of gauges or at least the specs that I'm supposed to adjust the stops to? I'm sure I can just use a piece of cardboard that I measure out with a ruler to get the adjustments, but I can't quite make out the measurement on the picture of the manual I downloaded.

  10. #9
    FrankieSixxxgun is offline Cadillac Owners Fanatic
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    Re: '87 Q-Jet Adjustment Question

    That's the one. I just got the tools to adjust the stops and need to see how the gauges work. Do you remember the spec for adjustment? For some reason 7/16" is sticking in my head.

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