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How do I adjust my fuel/air mixture on my truck?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by weisel, Mar 19, 2001.

  1. weisel

    weisel 1/2 ton status

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    How many turns out, or however it goes? I have a 77 k5 with a 400 engine, and stock carburator. I can really smell the truck running too rich.

    Insurred by Smith & Wesson
     
  2. muddin4fun

    muddin4fun 3/4 ton status

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    are you blowing black smoke out the exhaust?

    [​IMG]


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  3. Blue85

    Blue85 Troll Premium Member

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    You can only adjust the idle air/fuel mixture unless you change jets. The problem could be a sticking choke or vacuum leak, too, so check those first before changing the settings on the carb. If it's also idling rough, it could be an ignition problem. The carb is usually the last thing that you want to adjust when "tuning up"

    <font color=green>Stupid tourist at Mammoth Cave, Kentucky: "How many miles of unexplored passages are there?"</font color=green>
     
  4. RaisedK5

    RaisedK5 1/2 ton status

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    Like the previous post said, check out everything before playing with the carb, but if everything checks out heres what you do, first warm it up, then remove the vac line from the evap can and plug it, remove the vac advance from the dist. and plug that, then look at your aircleaner lid, it should have a sticker with some numbers, timing, gap, idle etc. my idle is 800/700 which we'll get to in a minute, mine you leave in park, read the sticker to be sure, then with the idle stop screw, (or solenoid if it has one) set idle (you'll need a tach, by the way) to the higher of the two numbers, now slowly back out the mixture screws equal amounts 1/8 to a 1/4 turn at a time, idle should increase, keep going until it stops increasing, then reset idle with the idle stop to the higher number, now reverse the process, screw the idle mixture screws in in equal amounts 1/8 to 1/4 at a time untill idle drops to the lower of the two numbers. and thats it, i just did mine this past weekend, and man does it run better and cleaner, (my smog checks comming up).
    have fun,

    RaisedK5

    "Friends don't let friends drive Fords"
     
  5. weisel

    weisel 1/2 ton status

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    I was just playing with it today, and got confused. I don't know what any of this junk is on this carb. This is my first Chevy, so I don't know what everything looks like. I think I'm just going to buy a rebuild kit and spend a day becoming friends with this new gizmo. After I do all the other tune up stuff. Who sells a good rebuild kit with good instructions?

    Insurred by Smith & Wesson
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    Idle mix is adjusted by the two screws at the front base of the carb. Depending on year, they can be phillips or flat blade, or on later ones, they will be flat, and you need a 12 point socket of the right diameter or a piece of crushed tubing to adjust them. Turn them all the way in, and 3.5 to 4 turns is a good starting point. Gotta make sure idle is set too. Unless you know someone has messed with this setting, don't hit it first. If you want to rebuild the carb, then go for it.

    NOTHING controls idle mix but these idle mix screws. Primaries have nothing to do with idle.

    Dorian
    My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
     
  7. muddin4fun

    muddin4fun 3/4 ton status

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    I've got an edlebrock (carter) 600cfm on a 350. There are two screws on the front. On mine I tightened them all the way down and backed them out one and a half turns.

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