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Emissions and adjusting the Mixture?

Discussion in 'General Truck Info' started by misterturbo, Sep 19, 2007.

  1. misterturbo

    misterturbo Member

    Hi guys,

    I have a 91 Honda Acty which is having trouble meeting emissions up here in Canada..

    Since these trucks weren't equipped with catalytic converters, I installed one in however when I went to retest, the numbers were the same! A catalytic converter should reduce emissions by a large factor I thought..

    I am having trouble passing the CO portion, my numbers on idle are 1.77% with a limit of 1.50%, HC is also high, but passable 250 with a limit of 300..

    I have read that high CO is usually due to a rich mixture.. Does anyone know how to adjust the mixture?

    On my Honda, there is a plastic box on the top of the engine with two plugs. One plug has a screw which controls the idle, the other is a smaller screw covered by a cap.. I assume this would be the mixture screw? If so, do I turn it clockwise or counter-clockwise to lean out the mixture, and by how much should I turn?

    I did a search on the net for mixture adjustment, most sites said turn clockwise to lean.. But on a few, I read that you should turn counter clockwise?

  2. unclejemima

    unclejemima Member

    very good question. I have the EXACT same truck, but i live in alberta, where you can drive anything with wheels on it. Emissions, what that??? ;) Typical Alberta style!:eek:
    Regardless, i would like to help you solve your problem, as i'm having a problem to...bad gas mileage. To lean out the mixture would defiantly help solve both our problems.
    I played with my carburetor quite a bit now, mainly to lower my high idle. I did some big time adjustments on one of the adjustable thingies(tech talk:D) inside the carb, the one being the idle (mine was waaay to low, so i raised it) and the second the high idle problem on a cold start. I fixed the cold high idle by playing with the only other adjustable thing i could find shy of the regular idle screw.
    I adjusted it to the max, it was PITA!!!:eek: tiny 6mm socket and a tiny alen key was needed to do it, but now instead of 3300rpm when i fire it up cold, it only rev's 2500rpm now. Much better.
    I have a picture(not a very good one thou) at work of the internals of the carb, i will post it tomorrow morning. Perhaps some of the knowledgeable chaps can this forum can shed some more light. Mabey i just adjusted the mixture screw???
    Talk to you tomorrow,
  3. unclejemima

    unclejemima Member

    here you go. The pics are pretty bad, i might have to take another one.

    Attached Files:

  4. unclejemima

    unclejemima Member

    Well, i dunno if anyone has taken a look yet, but its been raining here the last few days, so i have not had a chance to take a better picture of the carb. Anyone else care to do so on an honda acty?
    Wolfman, i think my acty only has one rubber plug on the top of the carb cover, and i believe it is just to adjust the idle. Can you by chance take a pic?
    Best of luck with the emissions, how long before you have to get re-tested?
  5. misterturbo

    misterturbo Member

    Thanks for the input and photos unclejemima..

    I actually took the truck to my local Canadian Tires and they hooked it up to a gas analyzer and the tech adjusted all the screws including the one that you mentioned. Couldn't get the truck to pass after fiddling for an hour..

    Seems the truck runs nice and low under normal use.. but after coming back to idle it takes too long for the CO and HC to settle back down..

    No clue anymore, I don't even think the cat is doing anything, because readings are the same before and after cat installation. Got it nice and hot and still no difference..

    I am going to test my second truck and see if results are different..
  6. unclejemima

    unclejemima Member

    Yes please post the results. Very interesting. At least you have a second one to use as a guinea pig. What year is your other Acty? I know there are more Actys in Vancouver area, i wonder how they passed?
  7. Wolfman

    Wolfman Member

    Since the numbers didn't change, that just means that your old cat was fine. Since you have a guinea pig, try swapping out the oxy sensors if they'll swap across. If it's bad, the the feedback carb will keep the mixture turned up, thinking it's running too lean.
  8. misterturbo

    misterturbo Member

    I have two 1991 Acty's both basically the same..

    Wolfman, the Acty never had a catalytic converter from the factory, nor did they have any O2 sensors..

    I welded in a Cat. myself, but the numbers did not change, before a cat and after the cat was installed
  9. unclejemima

    unclejemima Member

    It does not give you much option to fix the emissions with these things. Far as i'm concerned, it can only be a carb issue. Perhaps a carb rebuild, or mabey it needs to be re-jetted? I am only familiar with motorcycle carb's, i know you can run bigger or smaller jets and adjust the needle clip to fix emission and fuel consumption, can the same be done to automotive style (acty) carburetors? To bad there was not an easier way to actually adjust the mixture with a simple screw!
    My acty is being a pig, approx 25mpg :( I need to get mine fixed, and i bet my emissions are HORRIBLE. Good thing i dont have to pass any aircare.
    Let me know how you make our misterturbo.

    out of curiosity, how does yours start? Do you need to use the gas pedal to help start it when cold or does it start on its own?
    Last edited: Sep 24, 2007

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