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Bad stumble/hesitation

Discussion in 'The Garage' started by 454k30, Apr 7, 2007.

  1. 454k30

    454k30 1/2 ton status GMOTM Winner

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    Just replaced my lifters and added some new msd wires. Set up initial timing at 8 degrees. When I connected the vacuum advance the timing advanced of course. With or without that hooked up I have a really bad engine stumble when I hit the throttle coming off idle. Makes city driving nearly impossible with the big surge. I calibrated the carb to max rich and that helped but it is still stumbles pretty bad. I am thinking that the carb itself might just be too small for this motor. I have a 454 with a 600 cfm carb. I had it running fairly well before the new lifters and wires but now it straight sucks. My thinking is that with these new parts I either got it mechanically sound and am finding out that the carb is too small, or I have a massive air leak somewhere in the manifold gaskets. I am thinking more towards the too small carb as I seem to have a ton of vacuum but I am not sure. its an Edelbrock 1406 carb, comp 4x4 cam. Initial timing 8 degrees, with vacuum hooked up at idle it jumps to 20.
     
  2. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    Sounds like a good old fashioned manifold leak to me!
     
  3. Thunder

    Thunder 3/4 ton status

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    I dont think your carb is the problem unless the accelerator pump is not working. Have you checked that?
    Also double check your plug wire fireing order. I have crossed a couple of wires and had similar problems
     
  4. 454k30

    454k30 1/2 ton status GMOTM Winner

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    Took the carb apart and found that the accelerator pump had no fuel in it. I suspect that the level the floats were set at were not reliably getting fuel into that chamber. I set the floats to allow a little more fuel in and problem is solved, so far no flooding. I do have a new problem though and that is carb related. I hadnt noticed before but while the engine is running there is a trickle of fuel constantly coming into the fuel filter. If the floats are up this shouldnt be happening. Thought at first it is bad needles and seats but when the motor is shut down the trickle stops. I have an electric fuel pump and yes it runs when the engine is shutdown. I am almost leaning toward a crack in the carb body that when the vacuum from the engine is applied leaks fuel into the intake manifold. Anyone seen this before?
     

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