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Original settings:Mixture screws (CV) and pilot screws (VM).

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    Original settings:Mixture screws (CV) and pilot screws (VM).

    I don't know why I have'nt figured this out before. Even our manuals don't mention this. We've all been told you can't move these screws and then put them back to their original settings. This may help you if you've moved the screws from their original factory settings and want to put them back, but you can't remember where they were.
    When the factory sets the screw, they "more often than not" put a "nick" in the carb body that's in line with one side of the screw slot. If your's don't line up, then they've been moved before. This nick will not tell you the # of turns out a screw is, but keep in mind on the VM carbs, the pilot screws (underneath) are generally 3/4 to 1 1/4 turns out FROM THE FACTORY. The side air screws are generally 1 1/2 to 1 3/4 turns out. The mixture screw on CV carbs is generally 1 1/2 to 2 turns out. I have yet to see factory settings of a full turn under or over the above settings, so you can see that the nick should help you in putting the screws back to where they were.
    As a side note regarding the VM carbs. The factory/emissions people don't want you to turn the side air screws but they are actually intended for fine tuning, especially when you ride in higher elevations. If you have trouble with re-starting and low speed riding in high elevations, try turning the screws OUT about a 1/4 turn or so. Return them when out of the high elevation.
    The mixture screw on CV carbs can also be adjusted to help with elevation problems, except you would turn the screw IN to counter the richening effect high elevations have on jetting.
    Of course if your bike has engine mod's and has been re-jetted correctly, these screws will not be in their factory settings. When tuning, the side air screws (VM) and mixture screws (CV) should be set to achieve the highest rpm possible and then re-set the idle to about 1,100 rpm with the idle screwknob. With the VM carbs, adjusting the pilot screw (underneath) will effect the mixture, so you have to re-tune the side air screws after making adjustments to the pilots screws. You may not notice any change in settings, but you should always do the re-check anyways.
    And on the seventh day,after resting from all that he had done,God went for a ride on his GS!
    Upon seeing that it was good, he went out again on his ZX14! But just a little bit faster!

    #2
    Keith wrote:

    The mixture screw on CV carbs is generally 1 1/2 to 2 turns out. I have yet to see factory settings of a full turn under or over the above settings,


    Two of mine were more that a turn off from the factory.
    I drilled out the caps myself so I know a previous owner didn't mess with
    them.

    #1 and 4 were 1 5/8ths turns out. ( in line with what you say)

    # 2 and 3 were totally bottomed out!

    Mo

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      #3
      #1 and 4 were 1 5/8ths turns out. ( in line with what you say)

      # 2 and 3 were totally bottomed out!
      I can second this, from my experience on my ZX-9 this spring. I put a Dynojet Stage 1 kit in it and had to drill out the stock caps, so I am 99% sure the PO did not touch them. The mixture screw settings ranged from 1.25 turns out to 2.25 turns out, with no consistency at all 8O . No wonder it ran rough and was a bit funky off the bottom...


      Mark

      Comment


        #4
        Well, I can't speak for every bike ever made, just the ones I've worked on. I'm just trying to help and pass along my experiences.
        If any mixture screws were buried, do you think the emissions test was done correctly on that bike? I don't think so. People make mistakes or do poor work all the time. Maybe the screws were never adjusted? A completely buried mixture screw could also indicate a cylinder that was running excessively rich during the test and an attempt was made to correct the mixture. If the bike fails the emissions test, and I think buried screws would be a sign, do they just cap the screw and pass the bike? I don't know what they do, just what they should do.
        On a stock, correctly tuned bike, the mixture screws wil be about 1 1/2 to 2 turns out, give or take a turn. So a range of 1/2 turn to 3 turns is their common factory set range.
        By the way mark m, these screws are for fine tuning the pilot circuit to supply the correct mixture to each cylinder. No two cylinders are alike as far as emissions is concerned. These screws regulate a second fuel passage into the carb throats. Because of differences in each cylinder, it's common to find these screws set differently from each other.
        And on the seventh day,after resting from all that he had done,God went for a ride on his GS!
        Upon seeing that it was good, he went out again on his ZX14! But just a little bit faster!

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