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rebuilt Q-jet tuning

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by aksidentproan, Oct 1, 2002.

  1. aksidentproan

    aksidentproan 1/2 ton status

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    I started up my new engine with my old Q-jet and she ran great. I took the old carb off and put a rebuilt Q-jet on it and it will run for 5-10 seconds and then cut off. I'm guessing its running to lean. There are 2 adjustment screws on the front of the carb. One with a spring which is closer to the driver side and one with no spring that is lower and toward the passenger side. Which screw is the idle adjustment and which one is the air/fuel adjustment. Which way do I turn them to raise/lower idle and to lean/richen the mixture. Sorry about all the questions and thanks in advance.

    Evan
     
  2. Burt4x4

    Burt4x4 3/4 ton status

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    The larger one near the linkage is idle adj. You can see it touches the stop on your linkage.
    The two screws on the very bottom plate.one on each side, are you mix screws.
    Turn them in,clockwise,to lean out or less fuel, turn out for more fuel,rich.
    The way I doit is witht he carb off you can see the little tips of the mix screws poking thru into the venturies(circle part) I turn them all the way in and then back them out about 3 full truns for a starting point, visually looking at the tips to see if they are even. Slap the carb back on and it should fire up as long as your float and needel are working. Next if you have a vacume gage hook it up to a main vacume source if no gage handy you can doit by sound. Start on one side and began to turn the screw in slowly pausing to listen to the motor and read the vac gage. you will hear it start to stumble or run ruff,stop now back it off until max vac is achived or the motor runs smoother. Do the same to the other side then adjust the idle and check the timming and now I do the same thing again and you should be all set!
    Hope this helps
    Good Luck
     
  3. florida4x4

    florida4x4 1/2 ton status

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    The rebuilt I just tried never ran better than the original. I finally took it back.
     
  4. aksidentproan

    aksidentproan 1/2 ton status

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    It turns out that sense I don't have power brakes the huge hole in the back that goes to the booster wasn't pluged in the rebuilt carb so I took the plug out of my old carb and it ran great.

    Evan
     
  5. Burt4x4

    Burt4x4 3/4 ton status

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    Cool man!
    Good Job!
    Late
     
  6. ak7

    ak7 Registered Member

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    Not sure if this is true all on setups but... That huge hole in the back of the carb, well I hooked it up to my booster and it did not have enough vaccum pressure for the booster to function. I was told the booster needs pure intake vaccum. That means you need to hook it up to the hole in the manifold that sits between the carb and the distributor. Just a little info for you that gave me an entire weekend headache. I would hate to see you run into the same problem if you installed a booster later on.

    ak7
     
  7. Burt4x4

    Burt4x4 3/4 ton status

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    That is how my booster is hooked up too, straight off the manafold. /forums/images/graemlins/thumb.gif
     

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