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New K5 Problem

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by BlueKnight, Apr 11, 2000.

  1. BlueKnight

    BlueKnight 1/2 ton status

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    Someone I work with drives a 83 Blazer. Motor is a 350 with a 4bb quadrajet carb recently rebuilt (1yr). We were at lunch yesterday and we were driving on the freeway. Under mild load going up a small hill. Suddenly the silly thing backfired through the carb. He let off the gas and we both looked at each other in dis-belief. So he put more pressure on the pedal mild load and it did it again. So he held it there and it kept doing it. He got upset and a mashed the accelerator and no back fire just power.Im perplexed. I was thinking stuck lifter or timing out of whack. But then again it could be the vaccuum advance. It was tuned up about 6 mo's ago Im confused.

    <font color=purple>79' K-5 396cid 600hp, TH350, NP203</font color=purple>
    http://79blueknight.homepage.com
     
  2. Goose

    Goose 1/2 ton status

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    Since the carb was just rebuilt, I wouldn't start there. It sounds like the vacuum or mechanical advance is sticking or messing up. I once had some mechanical advance weights rust enough that they didn't move and therefore didn't advance. (Too many water crossings I guess) When was the last time the distrubutor had any work done to it?

    '73K5,SM465,NP205,33"BFG,4"TuffCountry,3.73:1diffs
    350.4bolt+mods,Warn8000#,Factory skidplates
     
  3. Truckfan2

    Truckfan2 1/2 ton status

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    Check the timing, that happens when it's too advanced.
     
  4. SVBlazer

    SVBlazer 1/2 ton status

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    As an option, you might check the plug wires. They might be cross firing. HEI systems start dropping voltage above 3500rpm or so. This might explain why when WOT the backfiring stopped. The HEI wasn't putting out enough to bridge the air gap. Just a thought...
     
  5. BB454

    BB454 1/2 ton status

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    Go straight to the HEI. Had that problem before aswell. Can't remember what the "gremlin's" name was but-- found it inside the HEI I remember

    BB454
    IF IT DOES NOT HAVE 8 PISTONS - IT'S BROKEN !
     
  6. BlueKnight

    BlueKnight 1/2 ton status

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    all the above is possible. I will convey this info to him. Im thinking Dist for sure. Only thing that has nt been worked on.

    <font color=purple>79' K-5 396cid 600hp, TH350, NP203</font color=purple>
    http://79blueknight.homepage.com
     

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