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Sputtering at low speeds

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by kburnett, Apr 10, 2003.

  1. kburnett

    kburnett Registered Member

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    I just replaced the engine in my 71' Blazer and the thing runs like a top at idle and high speeds. However, when I am in neighborhoods driving slow or accerlerating slowly it sputters and misses, not real bad but noticeable to me. I have the electronic ignition from a 75' or later and the spark plugs to match at a .060 gap. I have also tried plugs from a 71' with a .035 gap. It also has a new edelbrock intake and carb. The plugs all look good carmel/tan in color and the timing is set at 12BTDC. I have changed the timing from 8BTDC all the way down to 16BTDC with no affect to the sputtering. I have changed out the distributor with a spare and changed out the cap and rotor and plug wires when I replaced the engine. I can't figure this thing out and the only recommendation that friends have given me is "Drive it like a race car and you won't have a problem". Do you have any ideas??

    I originally posted this in the wrong thread for 4x2's.

    thanks
    kent
     
  2. Roostr84

    Roostr84 1/2 ton status

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    There are alot more experienced guys here than I but my first instinct is to look to the carb for the problem. Do you know what kind of curve your distributor has?
     
  3. Topdown

    Topdown 1/2 ton status

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    I had a somewhat similar problem for a while... try moving the accelerator pump arm from the middle to one of the other holes. One hole will either make it worse or it wont change, the other will make it better. I moved mine to the top hole and the sputter/stall all but went away.

    -Ryan /forums/images/graemlins/k5.gif
     
  4. 69K5

    69K5 1/2 ton status

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    i agree with topdown.

    nathan
     
  5. kburnett

    kburnett Registered Member

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    I will give that a try tonight. I will post my results tomorrow.

    Thanks for your help.
     
  6. kburnett

    kburnett Registered Member

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    Ok, well I looked at the pump arm and it was already on the middle hole. I moved it to the bottom hole and the top to find out which one works best. One of them did indeed make it worse and the other made it better but the sputtering did not go away completely. I changed the timing around a bit and messed with the needle valves and that helped some but it is still there a little. I guess I just need to keep messing with the adjustments to find that "sweet spot".

    One question though. If I can't find that "sweet spot" would I need to replace or change out needle valves or anything inside the carb to get it right? For the most part it is a stock engine with an rv cam.

    Thanks for all your help.
    kent
     
  7. Anthony72K5

    Anthony72K5 Registered Member

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    I had a slightly bent valve and my motor was acting similar.

    It would idle fine, and tach up with no problems, but taking off would sometimes make it sputter a bit.

    At higher RPM it wasn't a problem. I imagine having one cylinder not firing right has a strange scavenging effect on low RPM performance with a load on the engine.
     
  8. kburnett

    kburnett Registered Member

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    A bent valve may may sense as I just removed my plugs and all but one looked normal. The one bad one looked wet with oil, extra carbon buildup and the threads were wet as well. I think I may have bought a bad crate motor. It's under warranty so not too big of a problem except that I will still have to remove the head(s).
     

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