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Carb Troubles, have ?'s

Discussion in 'The Garage' started by Hossbaby50, Sep 18, 2003.

  1. Hossbaby50

    Hossbaby50 3/4 ton status

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    Carb Troubles, have ?\'s

    '85, 350 w/Qjet, MSD (box, coil, wires), all emissions equip.

    I have tried changing cap, rotor, plugs, checked wire, adjusted timing, played with the idle mixture, changed the fuel pump & filter, and I still can't nail down the problem.

    My truck is running pretty bad. I think I have narrowed it down to the carb or possibly emissions equipment. I was having problems with my truck trying to die at idle. I could feel it stumble and see the RPM's jump around on the tach. I played with my timing and idle mixture, but it didn't fix the problem. I have tried my timing all over the place and adjusted my idle screws all the way in and then backed them out.

    Adjusting the idle mixture out cured the idle jumping for the most part, but now I am getting my truck to die at light throttle and cruise. If I punch it then it runs fine, but if I try to cruise or lightly accelerate it jumps around or dies. Anyone have any idea on what could be wrong?

    What will a truck run like with a bad EGR valve? I know my carb could cause this, but what is wrong? THanks

    Harley
     
  2. 88Silverado

    88Silverado 1/2 ton status

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    Re: Running like crap, need answers (carb?)

    Sounds like you may have a vacuum leak.
    May also try changing the O2 sensor. Theyre pretty cheap.
     
  3. Hossbaby50

    Hossbaby50 3/4 ton status

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    Re: Running like crap, need answers (carb?)

    No O2 sensor. I am not fuel injected.

    I have also looked over my vacuum lines pretty well and can't see any damage to them.
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    Re: Running like crap, need answers (carb?)

    Bad EGR can weak havoc at idle and all other engine speeds.

    A decent test is to push up on the underside of it while the truck is running. It *should* kill the motor.

    A problem with this test is that if the valve is "stuck" partially open, it still introduces exhaust gas at idle, but it could be just enough to cause problems, not enough to kill the engine. Even disconnecting the vacuum line won't change that.

    Might be able to manually "cycle" the EGR valve by depressing the underside of the valve completely, then letting go. Carbon builds up on the stem and can limit its travel.
     

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