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Backfiring through the Carb on acceleration

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by dlferry, Apr 9, 2006.

  1. dlferry

    dlferry Registered Member

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    I have a newly rebuilt Chevy 355 Gen 1 block. It runs and idles great however it from time to time backfire through the carburetor on acceleration. I currently have the timing advanced 24 degrees. I am thinking it is carburetor related but not sure. Am I on right track?
     
  2. OrangeCrushK10

    OrangeCrushK10 1/2 ton status

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    Wouldn't be a Carb problem I don't think. Sounds like an intake valve issue. I'd say burnt intake valve, but you said it was just rebuilt?

    Perhaps the valve is sticking or not closing all the way?
     
  3. littlejimmythatcould

    littlejimmythatcould 1/2 ton status

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    Once in a great while mine would do that when it's cold. But I put a new carb on it and it fixed it. i don't know how but it did. Plus the carb I was running was probably eight years old and had vaccuum leaks all over it. Swapped a new one on and now everything (especially my brakes) work better. Now I'm just having trouble with detonation.... trying different metering rods. Maybe your timing is too high. Mine only runs at I believe 12 to 14 degrees advanced, but I have points ignition.
     
  4. farshot1

    farshot1 Surrender the Booty

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    Possible that the vacuum advance is bad.
     
  5. 1985_K5_Silverado

    1985_K5_Silverado 1/2 ton status

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    Which brand and model number is your carb? Does it do the carb backfire thing on light acceleration, but not when you really punch it?
     
  6. 73k5blazer

    73k5blazer Unplug the matrix cable from the back of your head Premium Member

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    Mabey running too rich, or getting to much gas too quickly. My holley was like this when I put it on my 4.3lv6 (390cfm holley), i had to put A smaller shooter and a different pump cam in to get rid of it.
     
  7. 78Suburban

    78Suburban 1/2 ton status

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    24* sounds like Alot of initial advance. Are your valves adjusted properly?
     
  8. mrk5

    mrk5 The Sticker Guy Moderator Vendor GMOTM Winner Author

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    Here's something I found:
    24* is a lot. I have mine advanced 15* and I live at 5000ft.

    Where is your vacuum advance hooked up?

    HEI dist? From what year?

    I'm asking because I'm wondering if you have your initial timing set really high and it is compounded by vacuum advance making it even higher.
     
  9. johnathan

    johnathan 1/2 ton status

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    Mine used to do that from a lean condition Chek for manifold leaks and could just be the carb.Does it surge any at light acceleration?What carb?
     

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