Quick answers for high HC at idle

Discussion in '40- & 55-Series Tech' started by xrock, Nov 7, 2005.

  1. xrock

    xrock

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    I did a search for emissions it brought back 8 pages and after looking through the first 4 and not seeing the answer, I just figured it would be quicker to ask.

    Sorry-

    So, I took the emissions test this morning on the new to me- 1972 FJ40 and it passed everything except for the Hydrocarbons at idle.

    Loaded reading: 94 - (400 is acceptable)
    Idle reading: 974 - (again, 400 is acceptable)

    1- Why would it vary SO much between loaded and idling? 94 to 974
    2- Is there a quick fix like pouring some of the cleaner into the carb to get it to pass real quick?

    Thanks for the input
     
  2. dfmorse

    dfmorse

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    Wow! I'm amazed it did that good.

    ...
     
  3. pbgbottle

    pbgbottle Forum Lifer

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    turn up the idle ? if you are allowed a maximum idle .i run mine through at about 950 rpm we are allowed a maximum of 1000 rpm at idle . thats in canada tho
     
  4. Pin_Head

    Pin_Head

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    High HC (and not CO) indicates that it is misfiring at idle. A common cause is a vacuum leak resulting in a lean mixture that is unable to ignite and a rough idle.
     
  5. xrock

    xrock

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    Thanks Pinhead- that sounds logical since it's ok when revved up, but not ok at idling speed.
     
  6. MandMAutomotive

    MandMAutomotive

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    What's CO at idle? If it's way low then it's to lean and you could turn out the mixture screws. Also check for vacuum leak.
    HTH
    John
     
  7. xrock

    xrock

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    CO was:

    Loaded: 0.23 (standard 3.75)
    Idle: 0.23 (standard 5.00)
     
  8. Pin_Head

    Pin_Head

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    You could try adjusting your idle mix to see if it smooths out. I just assumed that everyone does htat as a part of tuning it up.
    If it doens't smooth out, check for a vacuum leak.

    The other possibilities aren't good ones:
    The compression is too low in 1 or more cylinders to support reliable ignition at low RPM. Also leaky exhaust valves tend to show up as high HC at idle because the air/fuel mix (HC) leaks past the valve during the compression stroke.
     
    Last edited: Nov 7, 2005
  9. MandMAutomotive

    MandMAutomotive

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    CO is low, HC high. Backing out the mixture screws will rasie CO and lower HC.
    If you go to far you may fail CO. It's only guessing without a gas analyzer.
     
  10. xrock

    xrock

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    Good info. We checked for vacuum leaks- None!

    Checked the spark plugs and they're fine. Adjusted the mixture a bit, corrected the timing and raised the idle speed. We even cleaned out the carb a bit.

    Went back this morning and retook the test.

    HC
    Loaded: 74 - Standard 400 (was 94)
    Idle: 753 - Standard 400 (was 974)

    CO
    Loaded: 0.14 - Standard 3.75 (was 0.23)
    Idle: 0.59 - Standard 5.00 (was 0.23)

    So again everything is in line except for the HC at idle. It did go down from 974 to 753. I guess my question is: Should I just go in and adjust the mixture some more? I still have plenty of room on the CO side to overcompensate.

    Or is there something else I should try?
     
  11. MandMAutomotive

    MandMAutomotive

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    Yes.

    How many turns out were you and how many now??

    John
     
  12. petescoffee

    petescoffee

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    wouldn't a temporary catylitac converter fix the HC's.
     
  13. pbgbottle

    pbgbottle Forum Lifer

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    my thought exactly . or another option do they check vins there?? . i allways run my rig through for a friend with his plates on .they don't check vins here . HA! he can't seem to get his dialed in either ?? HC's can be snuffed out with a cat i run one on my small blocked dailly driver rig no big deal . straight through design .
     
  14. DSRTRDR

    DSRTRDR I can mangle anything ... SILVER Star

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    xrock,

    what's your idle speed now? We had exactly the same problem you describe, high HC at idle only, everything else way low. We found that idle RPMs were too low, now at 650-680 rpm, vacuum is 18-18.5. Haven't gone for retest yet.
     
  15. xrock

    xrock

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    I didn't do that part, so I'll have to ask.

    I'll go out and look at the idle, but I believe it's around 600 or a little higher. I tried to turn it up a little more before the exam but it appears to be turned all of the way. I was trying to turn it clockwise and it appeared maxxed out.

    What is involved in a "temporary" catylitac converter?
     
  16. Pin_Head

    Pin_Head

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    Does it idle rough and act like it misfires? If so, it still sounds like a lean mix problem. A cracked intake manifold bottom or a leaky EGR valve (do 72s have them?) can create a vacuum leak that is hard to fine. The ohter possibility is fuel supply, but after you have turned the needle out 4-5 turns, there is little change in the mix. The idle circuit could be plugged, but when this happens it usually won't idle at all.

    If it idles smoothly and this doesn't change when fooling with the idle mix screw, then check the compression.

    As a practical matter, the simple solution may be to bump up the idle speed to the maximum allowed and see if that passes.
     
  17. xrock

    xrock

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    It doesn't really idle rough- It does sound like it's missing a little bit though- that's why we looked at the spark plugs to make sure they weren't gunked up.

    I was able to turn the idle up a little more.

    For my problem though, should I turn the mixture screw clockwise or counterclockwise? (sorry, I'm new to carbs)
     
  18. MandMAutomotive

    MandMAutomotive

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    Turn them out, counter clockwise
     
  19. xrock

    xrock

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    OK- tonight, I'll:

    1- Raise the idle to just under 1000
    2- Turn mixture screw counter clockwise (any advice on how many turns)
    3- Rubbing alcohol in the gas tank (recommended by a friend- thoughts?)

    and try again tomorrow morning.

    If I Fail again, then I'll talk to a muffler shop about adding a catylitac converter.

    Thanks everyone for you thoughts and help- hopefully, I'll knock it out tomorrow.
     
  20. RHINO

    RHINO

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    the idle mix screw was out at least 4-5 turns at first,, i went to adjust but it wasnt making any difference like it should, so i screwed it all the way in and nothing, no kill.
    idle screw is at about 2 turns out right now.
    vacuum is also low at around 14-15".
    timing was advanced out the window, its set at 8* now.
     
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