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Rich or Lean Carb?

Discussion in '40- & 55-Series Tech' started by preacherman, Mar 17, 2003.

  1. preacherman

    preacherman

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    My carb is either running to rich or too lean. It backfires when cold (untill it warms up) and pings on the highway at about 2400-2700rpm. I just moved from high altitude to low and I am thinking the carb now needs adjusted. I need advice to rich or too lean? And when I adjust it how do I adjust it just right? I have a 1987 FJ60 and the carb is only two years old.
     
  2. JasonH

    JasonH

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    Just a guess here, but have you checked your timing? Your distributor has a dual advance with the smaller diaphram being a high altitude compensator (HAC).
    From your description, it sounds like your timing is too far advanced - and since you just changed elevations that might make sense. It could be that your HAC isn't working and didn't retard the timing back for the lower elevation.

    ???
     
  3. theo

    theo

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    The amount of fuel being metered into the intake is the same as it was before you moved because it's based on liquid volume, which doesn't change much with elevation.

    But the air got thicker when you moved to lower elevation, because gases become denser with increasing pressure. So, you are lean (same fuel but more air).

    You can change the idle mixture screw(s) to get a richer idle, but you probably won't be able to change the off-idle mixture without rejetting.

    Pinging, especially under load, usually indicates timing too far advanced. Try retarding the timing a degree or two.

    **Oh, what a dope I am. Try Jason's tip first. ** :p
     
  4. landcruiser

    landcruiser

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    Back firing when cold and pinging when warmed up are both symptoms of a lean condition. Lean mixtures will cause your engine to run hotter and that creates hot spots and pinging. There is a possibility of engine over heating or other damage occurring especially when the weather warms up. Better have FJ40Jim look at your carb.