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Thread: off the line heasitation
          
   
   

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  1. #1
    kdogmcool's Avatar
    kdogmcool is offline CHR Member Visit my Photo Gallery
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    Car Year, Make, Model: 79 GMC street coupe
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    off the line heasitation

     



    ok so i got my truck running...(thank god)chev 350 edelbrock intake holley 570 cfm carb. anyways it runs great but i have a stumble off the line. It goes away when the secondaries open and seems to be quite resposive at higher rpm but off the line nothing. I have played with the fuel to air mix.getting the most vacume at the intake.timing is set to 12, have tried at 14,10,8,same. Float levels are good. could it be the pump shot or accel pump on the carb. i get a steady shot of fuel out of the pump shot. could it not be enough or to much? how do you tell?

  2. #2
    R Pope is offline CHR Member Visit my Photo Gallery
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    Stumble like that is usually caused by either a lean carb or retarded timing. Sometimes it's a weak spark, or bad plugs or wires. With that carb it isn't overcarb'ed, as long as the secondaries aren't opening too soon.
    Does it only do it when you floor it, or every time you give it a little gas to get moving?

  3. #3
    63BoxNova's Avatar
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    I had the same problem, I increased my pump shot and no more stumble. In my case it was a lean condition...if I remember correctly I went from a 31 to 37 pump shot. It was a cheap fix, which is a rare occurence

  4. #4
    erik erikson's Avatar
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    Quote Originally Posted by kdogmcool
    ok so i got my truck running...(thank god)chev 350 edelbrock intake holley 570 cfm carb. anyways it runs great but i have a stumble off the line. It goes away when the secondaries open and seems to be quite resposive at higher rpm but off the line nothing. I have played with the fuel to air mix.getting the most vacume at the intake.timing is set to 12, have tried at 14,10,8,same. Float levels are good. could it be the pump shot or accel pump on the carb. i get a steady shot of fuel out of the pump shot. could it not be enough or to much? how do you tell?
    You got it.
    Check you acc. pump.

  5. #5
    Dave Severson is offline CHR Member/Contributor Visit my Photo Gallery
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    And the old question, which port are you running your vacuum advance off??? Try the other one...see if that makes a difference.
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  6. #6
    kdogmcool's Avatar
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    It only happens when i go slow off the start. if i floor it then it seems to go away.... i have tried to go from timed port to full vacuum for advance. no change. spark plug wires, plugs, cap,rotor,coil, carb and intake are all new.

  7. #7
    skids72's Avatar
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    I recently went through similar problem... hesitation taking off normally from a stop light I could fix with about 2 degrees more advance. Launching hard (flooring it) I went up on pump nozzle size to squirt sooner (I'm assuming this is a double pumper?) from #31 to #40 was too far... #37 sounds about right 63BoxNova...

    Chris

  8. #8
    R Pope is offline CHR Member Visit my Photo Gallery
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    Is the acc. pump squirting with a very small throttle opening? Holleys use a cam to actuate the pump, can you move the cam so it works the pump sooner?

  9. #9
    Sidedraft Deuce's Avatar
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    Quote Originally Posted by kdogmcool
    ok so i got my truck running...(thank god)chev 350 edelbrock intake holley 570 cfm carb. anyways it runs great but i have a stumble off the line. It goes away when the secondaries open and seems to be quite resposive at higher rpm but off the line nothing. I have played with the fuel to air mix.getting the most vacume at the intake.timing is set to 12, have tried at 14,10,8,same. Float levels are good. could it be the pump shot or accel pump on the carb. i get a steady shot of fuel out of the pump shot. could it not be enough or to much? how do you tell?

    Every Holley that I ever checked for friend had the same problem. The pump adjustment is not set right. Have your Buddie hold the carb wide open because you need three hands to do this right. Now press the pump lever(the one that go's under the carb) until it is all the way down. With the carb in this position set the clearance from the cam arm at .015". Most novices set this adjustment at idle. If you still have a bog after this you most likely have a vacuum leak.

  10. #10
    Sinister's Avatar
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    Hey guys, What if he used lighter advance springs on the distributor weights?

    I thought the mechanical part of it got you from off idle to part throttle, then the vacuum took care of the rest of the timing. Please correct me if I'm wrong though.

    Adam
    I ain't dumb, I just ain't been showed a whole lot!

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