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Thread: Carb newbie | Rear carb smoking?

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    Registered User TBone028's Avatar
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    Default Carb newbie | Rear carb smoking?

    I have yet to dig into the wonderful world of SU carbs and have a general question. What does it mean when a carb is lightly smoking?

    Right now, the carb closest to the firewall (I believe that is considered the rear carb, please correct me if Im wrong), smokes at idle. Its very light, and I can see just small wasps of white smoke. What does this indicate? There isnt any backfiring, and the car runs well. No hesitation and excellent drive-ability. According to my A/F ratio gauge, I'm running just slightly rich (exhaust mounted wideband o2 sensor).

    Any help/insight as to what this indicates would be greatly appreciated.
    1972 240Z - 3.1L with some goodies
    1974 260Z - SOLD!

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    Registered User Zforce's Avatar
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    Sounds like either an intake valve is burnt or way out of adjustment (too tight)

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    Registered User Terrapin Z's Avatar
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    Check the carb balance too, one could be rich and the other lean, giving you the A/F reading, but not not being correct.

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    Do you have a water or oil leak dripping on the exhaust?

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    Registered User TBone028's Avatar
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    No, its coming directly from the carb. I can see it. I do have a colour-tune, I should check to see where I'm at as far as mixture per carb, just havent dont it yet. I also have a sychrometer that I have yet to use as well. Just thought I would post to get some ideas while Im at work.

    And yes, I do think my valves need to be adjusted. I know its part of the tune-up process. Just havent had a chance to yet and dont have the correct tools to set them properly.

    Thanks everyone, I'll post back after I see whats going on.
    1972 240Z - 3.1L with some goodies
    1974 260Z - SOLD!

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    Registered User TBone028's Avatar
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    False alarm, the smoke was coming from the crankcase hose being vented back into the stock 240Z air filter housing...I'm pretty surprised that I had that much smoke coming out of it. Should I see that much smoke coming from the crankcase?!? Its very visible light white colored smoke. What is considered "normal"?
    1972 240Z - 3.1L with some goodies
    1974 260Z - SOLD!

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    I knew there was a reason I didn't want to jump into the middle of this one.
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  8. #8
    beandip beandip's Avatar
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    There is a vent hose that runs from the pan to the underside of the intake manifold. Where it attaches to the intake there is a PVC valve. It could be stuck . I cleaned mine with a small amount of gas in a soup can to dissolve any gunk. Just check it by sucking on one end and it should not allow flow but drawing from the other end it will. If it doesn't seal buy a new one. It is basicly a check valve. This draws gases from the crank case and they are burned by the engine. If it is stuck the engine will build sludge.
    this could be the cause of the smoke that you are seeing.
    Gary
    I'd rather die while I am living than live while I am dieing. CZC 1887 IZCC 12602 Member of NorthWest Z Car Club

  9. #9
    Registered User TBone028's Avatar
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    This is why I love classiczcars.com. Thanks Beandip! I will check it out later this evening/week.
    1972 240Z - 3.1L with some goodies
    1974 260Z - SOLD!

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    Registered User TBone028's Avatar
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    So after I replaced the PCV valve, I'm still seeing smoking from the valve cover breather. I know that it should be sucking air from the air cleaner housing, not venting blow-by gas into the air cleaner housing. The FSM says that engines with excessive blow-by will experience this type of venting in all throttle conditions. All of the other emission control equipment has been previously removed.

    My question is, would improper valve adjustment be part of the excessive blow-by? When I picked up the car, he told me it was something I should do in the near future. Also, the previous owner told me the motor was rebuilt about 5000 miles ago. I would think that the rings would be fine...any ideas or suggestions? All the lines are clear and unobstructed. Not sure why all the blow by is occurring.
    1972 240Z - 3.1L with some goodies
    1974 260Z - SOLD!

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