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Need carb help - continuously backfiring

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by schwinnd, Mar 8, 2002.

  1. schwinnd

    schwinnd 1/2 ton status

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    I have a stock 350 with a very old quadrajet. It is backfiring almost continuously. I can get it to run smoothly for a couple of minutes, then it starts backfiring. I just put new heads on the motor, the distributor is in correctly and the timing is fine, new plugs, old wires, new dist. cap rotor. The motor ran fine for about 30 minutes to get it timed and adjusted, then I took it out for a drive and it ran great for about 15 minutes of highway and in town driving then it started backfiring and missing and hasn't ran since last Sunday. The sound it makes is a short 'pop.....pop.....pop....Kind of like its out of time but it's not. Any help would be very appreciated. I'm not opposed to going to buy a new carb, but would like to know if that is really my problem.

    Thanks,
    Dave
     
  2. Stomp

    Stomp 1/2 ton status

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    This may sound silly, but, I'm serious not being an a$$. Did you check the plug wires to make sure they hooked up right? I bought my first chevelle with a simular problem to yours, took it home and found that was the only problem
     
  3. TopOff

    TopOff 1/2 ton status

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    Since new heads... could also be valves are too tight.

    But I am leaning to the wires too.

    Good Luck.
     
  4. schwinnd

    schwinnd 1/2 ton status

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    yep, I checked the wires, everyone is going to the right place. Could bad wires cause this?

    Thanks for the quick responses.

    No, the valves aren't too tight. I pulled the valve covers also, to check that I hadn't done any damage to the push rods or valve springs.
     
  5. 502Burban

    502Burban 1/2 ton status

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    You may want to check your distributor to see if the advance weights are sticking. Might have a broken return spring on the weights. This would have your timing fluctuating, causing the backfiring.

    Just an idea...
     
  6. Skigirl

    Skigirl 1/2 ton status

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    Mine did the same thing until a friend of mine found that the distributor had been put on one tooth off. Of course, there would then be no way to advance the timing enough.
     
  7. mdm365

    mdm365 1/2 ton status

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    yes bad wires will cause that and the firing order is off . here is the order 1-8-4-3-6-5-7-2 the way the dist turns i belive is clockwise. hope this helps---- mike m
     
  8. garagelogic

    garagelogic Registered Member

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    Didn't say what year the engine is, but it could be the catalytic converter.
     
  9. Redfrog

    Redfrog 1/2 ton status

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    maybe a flat lobe on the cam? just a thought....
     
  10. k30gambi

    k30gambi 1/2 ton status

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    My dads 76 ran like crap all of a sudden one time. I re-adjusted the valves and still would backfire up through the carb at any time. He bought some new spark plug wires and its run fine since
     
  11. chevyracing

    chevyracing 1/2 ton status

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    If you checked the wires and all is okay look for a bent push rod on the exhaust side of the valves. During the intitial fire up you may have had one too tight and it took a whack by the piston causing the exhaust valve not to open.

    John
     
  12. chevyracing

    chevyracing 1/2 ton status

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    one more thing too. Check to make sure the carb did not get any crap down it when you had it all apart. If the jets got something in them that will also cause the problem as well, especially on an Edlebrock carb if that is what you have. The Edlebrock is very touchy to crap in it.

    John
     
  13. schwinnd

    schwinnd 1/2 ton status

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    Re: Need carb help - continuously backfiring **UPDATE**

    Thanks for responding everyone. It turned out to be a valve that I forgot to adjust and the rocker arm was loose./forums/images/icons/blush.gif I get the retard motor building award/forums/images/icons/frown.gif But it runs great now, thanks for the help. I just drove it about 15 minutes ago and it just hauls. Those new heads make it run like a dream/forums/images/icons/cool.gif. BTW I did put new plug wires on it.
    Thanks guys!!
     

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