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Thread: Carb Adjustment

  1. #1
    Senior Member TonyR's Avatar
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    I tried to follow this procedure last night. Thanks Shep for the image!







    On My other bike it is a single cylinder and the slightest touch of the mixture screw gives big RPM changes.

    On the CX I had it up to operating temp and all (side note the water return pipe will be hot and painful to touch... just so you know ) but when I turned the adjustment screw there was little idle change. I did not go more than 1 1/2 or 2 turns. I started from 2 1/2 turns out like Larry said to do. Seems to run and have power at that setting.



    Here :



    http://cx500forum.com/index.php?/top...dd-carb-issue/



    it is said that could mean a torn air cut off diaphragm. I replaced at least one of them, cannot remember which.



    Here:



    http://globalcxglvtwins.hostingdeliv...php?f=19&t=140



    it is said that the o rings in the air cut off diaphragm have a flat side. I did not notice an flat side on either of them. There may have been one but I did not see it. I looked very closely and remember pretty clearly because I was trying to be very precise.



    My question is how many turns should it take to impact the idle speed?

    Was I too shy about turning the screw. When I went in a lot (2 turns) the idle did drop and seem to falter but not like the little single does. I know two cylinders so the other cylinder will carry it that is why I am unsure how far to go.

    Thanks!
    1978 CX500 Running and Looking good
    1980 KZ250 LTD Single - Current paint victim... er ... project.
    1977 GL1000 NGW current project.

    Any day I ride to work is a better day than any day I drive to work.
    Any day I drive to work is a better day than any day I walk to work.
    Any day I walk to work is a better day than any day I am too sick to work.
    Any day I get to ride around all day and not go to work is beautiful!

  2. #2
    Super Moderator LRCXed's Avatar
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    Tony,

    The adjustment screws aren't so much an idle adjustment screw as they are a fine tuning mixture screw for the lower half of the rpm range. As an example, if they are set at 1 1/2 turns, idling fine, and you turn them to 1 turn, there may be no idle difference. But the difference it makes will be felt in the acceleration up the the 5K range where the main circuit takes over. Loss of power or hesitations will be felt. 2 turns or 2 1/2 turns out seems to be the optimal setting for most carb sets. But I have encountered several that needed to go 3 turns to smooth out any issues.



    The way I test the mixture screws and the low circuit is to turn them in until I hear the idle changing and note where that is before I turn it back out to 2 or 2 1/2 turns. Then I test the other side to see that it responds in the same amount of turns in. Sometimes I don't get an idle drop until it's around 1/2 turn out. But as long as they are near the same I know the circuits are clean and matched on both carbs.



    I start road testing at 2 1/2. If everything responds well, I'll turn it in 1/4 of a turn and ride it again. If that runs fine I'll turn another 1/4 in. I do this until I feel a difference in power then I'll back it out 1/4 to 1/3 and leave it there. There's no need to run them out any more than they need to be. A little rich is ok, but a little lean will be felt in power. This is why a plug will look black after sitting in the garage idling for a while while we work on the bike. They won't show the true color of the mixture until you take it out and ride it under a load. The plugs will reach full heat cycles that way and burn off any black soot that was built up while the bike sat running under no load. It may take 5 miles or more of riding to reach the heat range of the plug before you'll see the actual end results.



    It sounds like your set is clean and at it's best since they started to falter at 1/2 turns. Road testing around the neighborhood under 5K will tell you where the mixture screws need to be at for the bike to run it's happiest.



    Hope this helps explain why the screws didn't act like the single cylinder bike.



    Larry
    "If you're going to do something, "Do It Right" don't do it half assed"

    Carb rebuild book link, Book order link HERE

    78 CX500std.,GL650I daily rider, 79 cx500D, 78 CX500 restoration complete,
    many more waiting to get on the lift.

    Winter lowers order link.

  3. #3
    Senior Member TonyR's Avatar
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    Larry,

    Thank you again for an excellent explanation.

    The other write up made me think there would be a more obvious rpm change.



    I will monitor my plugs and see how they look.



    I am glad to hear from you on this I was confused.

    Tony
    1978 CX500 Running and Looking good
    1980 KZ250 LTD Single - Current paint victim... er ... project.
    1977 GL1000 NGW current project.

    Any day I ride to work is a better day than any day I drive to work.
    Any day I drive to work is a better day than any day I walk to work.
    Any day I walk to work is a better day than any day I am too sick to work.
    Any day I get to ride around all day and not go to work is beautiful!

  4. #4
    Super Moderator LRCXed's Avatar
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    No problem Tony. Sorry I haven't been on much to answer some of the carb questions. I've been very busy building the two bikes this last winter, and now am in the middle of doing a major spring cleaning of the shop and storage shed. But I'm trying to keep an eye on the board now and get caught up.
    "If you're going to do something, "Do It Right" don't do it half assed"

    Carb rebuild book link, Book order link HERE

    78 CX500std.,GL650I daily rider, 79 cx500D, 78 CX500 restoration complete,
    many more waiting to get on the lift.

    Winter lowers order link.

  5. #5
    Senior Member TonyR's Avatar
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    Quote Originally Posted by LRCXed View Post
    No problem Tony. Sorry I haven't been on much to answer some of the carb questions. I've been very busy building the two bikes this last winter, and now am in the middle of doing a major spring cleaning of the shop and storage shed. But I'm trying to keep an eye on the board now and get caught up.


    Larry, we all love seeing you here and appreciate all the effort you put in. No need to apologize about having a life off the forum! None of us feel you owe us anything.

    I may be out of turn by speaking for everyone but that is certainly how I feel and I imagine how the rest of us feel as well.

    Hope your bike projects are going smoothly!

    Tony
    1978 CX500 Running and Looking good
    1980 KZ250 LTD Single - Current paint victim... er ... project.
    1977 GL1000 NGW current project.

    Any day I ride to work is a better day than any day I drive to work.
    Any day I drive to work is a better day than any day I walk to work.
    Any day I walk to work is a better day than any day I am too sick to work.
    Any day I get to ride around all day and not go to work is beautiful!

  6. #6
    Senior Member DanCX500's Avatar
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    Dan

    My link to the cam seal delete plug
    '81 CX500c 41,000+ miles.
    CX/GL Wiki <------ Check here for help!
    Quote Originally Posted by Thumper View Post
    Always check the stupid stuff before panicking. This applies to everything in life.

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