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Back-firing through the carb, suggestions?

Discussion in 'The Garage' started by Okiemuddog, Jun 13, 2003.

  1. Okiemuddog

    Okiemuddog 1/2 ton status

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    Well, I got my pipes on my blazer and rebuilt my carb. I have got all my vac lines hooked up, but it is backfiring through the carb when you accelerate it hard, if you inch the throttle open then it does not do it. I am open to any suggestion as to where to start looking for the problem. I am still in the erly stages of getting this engine running correct, but would like to fix this problem fixed first.

    Oh, BTW I am running a stock 4bbl Q-jet from a '74 burb on a stock intake.
     
  2. Don

    Don 1/2 ton status

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    Check the timing with a light, vacuum disconnected and plugged at the distributor, sound's a little advanced by the way You described it. /forums/images/graemlins/eek.gif
     
  3. Twiz

    Twiz 1/2 ton status

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    Rule of thumb:
    Poping through the carb - it's lean, the engine is "looking" for more fuel to burn.
    Popoing through the exhaust - it's rich, the engine is still burning the fuel it has.

    Remember, a lean mix burns very-hot and quick. A rich Mixs burns slow and cool.

    [ QUOTE ]
    it is backfiring through the carb when you accelerate it hard, if you inch the throttle open then it does not do it.

    [/ QUOTE ]

    Based on the above comments.
    What do you think it could be ?
     
  4. Klink K5

    Klink K5 1/2 ton status

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    Timing could be way off or you might have a flat lobe on the camshaft on the exhaust side. My .02 cents.
     
  5. Zeus33rd

    Zeus33rd Smarter than you GMOTM Winner

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    About six months ago I had a problem with back firing from the carb. After much head scratching and parts purchasing- This is what the problem ended up being-

    This is the #6 exhaust lobe on the cam-
    [​IMG]
    /forums/images/graemlins/eek.gif

    This is the lifter that was on top of that lobe-
    [​IMG]
    [​IMG]

    My truck has been parked since and my big block is on the stand in the garage. /forums/images/graemlins/frown.gif
     
  6. XtrmChevy

    XtrmChevy 1/2 ton status

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    Check your spark wires, once I put them back wrong and the symptoms were similar... /forums/images/graemlins/tongue.gif
     
  7. sled_dog

    sled_dog 1 ton status

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    my K5 is backfiring throught he carb on acceleration to mine is becuase its running really lean and the accelerator pump isn't working right(its leaking actually) so its starved on acceleration.
     
  8. bigblock44k5

    bigblock44k5 1/2 ton status

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    could be timing but id have to say since you rebuilt the carb and it started doing it, fuel is the problem. my q-jet did the same exact thing. would pop unless i eased into. my solution...Holley!!! its perfect now.
     

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