Tuning Assistance

Discussion in 'The Venerable Q-Jet' started by jhems17, Jun 16, 2019.

  1. jhems17

    jhems17 Well-Known Member

    Hello and Happy Fathers Day to all the Dads out there. I am trying to tune up my newly refurbished Quadrajet from Quadra Jet Power. The instructions say to turn in idle air screws until engine stumbles then back out until I get highest vacuum or RPM. The more I back the screws out though the higher those two get without a limit. The screws are all loose and I'm concerned they are about to come out. Is there a different way to adjust the carb or a step or something I'm missing? Thanks for the help. (Also a whole run down on carb tuning would be great seeing as how the choke and other things are also out of tune:D) Thanks again.
  2. jhems17

    jhems17 Well-Known Member

    I am adjusting one side at a time. Should I be doing both screws at the same time? Also when I get the idle to where it sounds nice its at 700 plus but bounces from say 712 to 734. Should idle jump around that much? I can't get it lower so I must be doing something wrong I think I'm supposed to be 600 or 650 RPM at idle.. My vacuum bounces from 15 to 20 then it gets to the point where it bounces from 18 to 20 "Hg. Once again any help is greatly appreciated and the more info the better. Thanks.
  3. jhems17

    jhems17 Well-Known Member

    Okay, so I turned the idle air screws all the way in and of course it wouldn't start and stay running I went from 1.5 then 2 and it wouldn't start and run till 3 turns out. Then I kept turning them out (I turned them both half turn at a time going back and forth and giving a few minutes in between adjustments) until the RPM's reached 760ish and the vacuum was bouncing from 19 to 21 "Hg. That was the best I could get. So then I turned off the car and restarted it. RPMs are now at 850ish and I cant lower them. The idle crew is not even making contact with the throttle. Am I doing something wrong or is there some other issue. Once again thanks for any help.
  4. jhems17

    jhems17 Well-Known Member

    I just took the Riviera out for a cruise and I must say it was very nice. The idle was low and strong sounding. From a stop I pushed the pedal and it went forcefully. If I gave it W.O.T. it went faster no bog. I asked for power it gave power. If I gave a little more throttle I got a little more power, very responsive. After the cruise I checked idle RPM again and I'm still at around 800. Do I need to be lower or will this be fine? The engine has around 104,000 miles on it, I plan on a rebuild later, maybe with an old worn engine this is where it wants to be? I checked timing and at the 4 degree mark my timing light is at 15 and at the 0 mark I'm at 29 degrees. No vacuum plugged or anything so I don't know if that matters but just want to give as much info as I can. Thanks.
  5. BYoung

    BYoung Stage me

    Is it at 800 rpm in gear or in park or neutral?
  6. hugger

    hugger Well-Known Member

    Put the timing light on 0 and leave it there then check the timing with the vac hose disconnected and plugged. Put a second mark on the balancer 1.75 below the factory mark,...then read the power timing sticky.
    BYoung likes this.
  7. Dr. Roger

    Dr. Roger Stock enthusiast

    Don't adjust the idle screw (or the mixture screws) until the engine is up to temp as it will be on fast idle when the engine is cold and you can't adjust the regular idle screws. Idle should be set in drive. My 350 idles about 750-800 in park, but idles at 650 in drive.
  8. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    What you need to do is slowly back out the idle screws to get the best vacuum and RPM. Start with the screws about 1 1/2 turns out. When you go too far, the idle starts to "roll" a bit. When the RPM goes up more than 50 or so, back the idle screw out to lower it. Then fine tune the idle mixture screws. Turn them in and out in small increments and then see how the engine responds. It is time consuming. The engine, IF IT IS STOCK, should idle at 600RPM IN DRIVE (1971). Try adjusting it in gear. What I do is find a parking lot with a suitably high curb and let that hold the car in gear.

    I have no idea what you are describing when you talk about your ignition timing. The 4* initial timing is for the 1112077 stock 1971 distributor. In a nearly 50 year old car, parts get changed out all the time. You may have a different part number distributor in it. The only time an engine runs at the initial timing is at idle. Off idle and higher RPM, the timing increases. If there is a different distributor in it, the ignition timing specs for when the car was new goes right out the window. What you need to do is learn how to use a timing light and map out your advance curve to optimize it.

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