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Throttle stumble (cough, backfire through carb) at acceleration

Discussion in 'The Garage' started by Topdown, Jan 6, 2004.

  1. Topdown

    Topdown 1/2 ton status

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    Ok... I have nearly had it with these damn carberators.

    Brand new crate motor (less than 3k miles), I got the 350 HO Deluxe - carb to pan complete.

    It was running great the day before yesterday, today its running so bad its nearly undrivable.

    I can accelerate from a dead stop just fine, doesnt seem to be a problem. However, while "at speed" or 1/3 throttle I try and accelerate (2/3 throttle) and the damn truck all but dies. RPM goes up a little then down significantly and the truck seems to be starving out then it will backfire through the carb and catch back up.

    WTF?

    Help?
     
  2. big k5

    big k5 Registered Member

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    posssibly your choke is not getting enough power to operate correctly. my holley carb calls for a full 12v ??? maybe your distributor is loose and it's not quite in time ???? good luck, let us know how it turns out.
     
  3. chevystepside

    chevystepside 1/2 ton status

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  4. 72beater

    72beater 1/2 ton status

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    I have used some troubleshooting charts that have helped me in the past. here's one:

    http://www.recarbco.com/technical/newtrouble.html

    I have a better one at home that I'll post after work. I would check your vacuum first. If it is low look at timing. It's common for the distributir to slip in the yoke and throw timing off, which will cause problems similar to what you are describing. It also might be a malfunctioning choke. I have a manual choke and I see similar issues if it is not positioned excatly correctly.
    Ernest
     
  5. Topdown

    Topdown 1/2 ton status

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    Thanks for the info guys... I will start looking. /forums/images/graemlins/confused.gif /forums/images/graemlins/crazy.gif
     
  6. ZZ4x4

    ZZ4x4 1/2 ton status

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    So this motor and carb ran good for 3K miles then started doing this? Important to know in order to figure whether it is a set-up problem or a failure problem. Also, what carb do you have? If it's a Holley, the number is stamped on the air horn by primary inlet. Typically a carb backfire means too lean a mixture, or timing is too advanced. Can you provide more info?
    Jeff /forums/images/graemlins/usaflag.gif
     
  7. R72K5

    R72K5 Banned

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    does it do this all the time or just when colr, or just when hot ?

    without that info id have to say bad acclerator pump and/or low fuel bowl float adjustment and or ful delivery problem, IE weak pump and or line hose probolem somewhere from tank to carb.

    quadrajet are easy to take apart and clean out and put back together, it might just need a good cleaning out, thats all mine needed on the 83 after having sat drive never run for almost 5 years or longer maybe,

    if you could get a hld of a vacuum guage then i would connect it and make sure you are getitn 18-22 at idle speed and not irrgeular needle movements, if looks good there, then is most likely carb issue, carbs are great when are in godo shape taken care of and clean inside, also run an inline filter external and rid of the internal element small filter inside the front of carb, they like to plug up and sometimes the rubber valve in them jams up partially or completely and messes up fuel delivery.
     
  8. Confedneck

    Confedneck 3/4 ton status

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    how about vacuum advance hose? crossed up??
     

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