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Half my engine runs lean!

Discussion in 'The Garage' started by aksidentproan, Nov 30, 2003.

  1. aksidentproan

    aksidentproan 1/2 ton status

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    The driver side cylinders are all running lean. Ive adjusted the carb eight ways from sunday and still no change. I've got a rebuilt Q-Jet and an edlebrock intake manifold that has seperate inlets for the 2 sides of the carb. I'm not exactly sure what its out of but i know its a 350 from 69-74ish. Any info would be appreciatied.

    Evan
     
  2. k5guyva

    k5guyva 1/2 ton status

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    These carbs have 2 mixture screws. The newer Q-jets with CCC (computer control) have a solenoid in them for the mixture. But a 70s engine shouldn't have one of these. My bet is that you need to take the carb out of the engine and clean the dickens out of it with cleaning fluid. The mixture is done with needles and some dirt would stop it from adjusting.
     
  3. 84_Chevy_K10

    84_Chevy_K10 Banned

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    [ QUOTE ]
    The driver side cylinders are all running lean. Ive adjusted the carb eight ways from sunday and still no change. I've got a rebuilt Q-Jet and an edlebrock intake manifold that has seperate inlets for the 2 sides of the carb. I'm not exactly sure what its out of but i know its a 350 from 69-74ish. Any info would be appreciatied.

    Evan

    [/ QUOTE ]

    Are you sure you don't have an intake gasket leak?
     
  4. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Do you have a dual plane intake? With a dual plane it would be running leane on every other cylinder on both sides. With just one side you either have a single plane intake or you have a vacuum leak.

    I just had a simular problem with my FI 454 Burb. IU have dual plane so it was every other cylinder. It was a Bad gasket under the throttle body.
     
  5. thatK30guy

    thatK30guy 1 ton status Premium Member

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    What would the motor run like under a load? I'm asking because my truck seems to run lean on one side under load, but in neutral or park, it seems to run fine. Would this be a vacuum leak or possibly the vacuum modulator? /forums/images/graemlins/confused.gif
     
  6. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    [ QUOTE ]
    What would the motor run like under a load? I'm asking because my truck seems to run lean on one side under load, but in neutral or park, it seems to run fine. Would this be a vacuum leak or possibly the vacuum modulator? /forums/images/graemlins/confused.gif

    [/ QUOTE ]
    Is it a TBI motor? It plays hell with the TBI or TPI. The vac leak runs half the cylinders lean. The O2 see's a blend of the lean and proper running cylinder (if it is Dual plane or if it has a O2 for both sides). To get the reading back where the ECM thinks it belongs it runs 4 cylinder rich to adjust for the 4 lean to make the average read the proper mix.

    It would idle ok but had a slight miss. It ran ok under load as well but since none of the cylinders had a proper stoic fuel load it was down on power. I didn't know this because it was like that when I bought it. So once I fixed the leak it felt a lot stronger. MPG came up 1/2 mpg.

    It also fixed a high idle problem it had. It was idling 1,000 in gear. It now idles at 750-800 in gear. Lowering the idle helped with a heat up problem I had with both the engine and transmission when stuck in traffic. Oil temp would come up to 250-275 after getting off the hwy and the tranny would creep up to 200. The extra heat would start to overwhelm the cooling system (it had a plugged up radiator). Now my oil temp runs about 10-15 degrees higher then coolant temp. Transmission runs about 180 all the time.


    I went through this on my Supra. I had 1 bad injector that was running lean. ECM adjusted for it. Finnaly burned both exhaust valves on that cylinder. /forums/images/graemlins/rolleyes.gif
    Once I got that fixed it ran much better and got better MPG.
     
  7. sled_dog

    sled_dog 1 ton status

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    I didn't see anyone mention it, an exhaust leak at a header or manifold can make one side of the motor run lean compared to the other one. leak means ehxaust flows "better" that changes the rich/lean condition. happened on my dad's race car, replaced header gaskets and it went away.
     

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