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Thread: Tuning S&S card on FXDL after rebuild

  1. #1
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    Adjusting S&S carb on FXDL Dyna after rebuild

    1997 Dina FXDL Lowrider

    My S&S super E carburetor was leaking from the overflow tube and it turned out the accelerator pump diaphragm and boot were both torn. It was almost same cost to get a complete rebuild kit and I figured it could use it so that's what I did.
    I then followed the instructions to put the Idle mixture screw, Idle speed screw, and Accelerator adjustment screw at the factory settings before warming up the engine to make the idle adjustments.
    But now the bike fires up fine but revs high like crazy even after warming. And turning the idle mixture adjustment screw either direction and turning the Idle speed screw all the way out doesn't seem to do anything.
    Any advise?

    Other possibly relevant (or not) pieces of information:
    1) The kit came with two different idle mixture needle screws. The one that looked exactly like my old one seemed to have bad thread and I did not want to force it. So I tried the other one. But after seeing how the bike was running put the original old one back in, which doesn't seem to have anything wrong with it, and it's still doing it.
    2) Did NOT change any of the jets. But did clean them thoroughly with brake cleaner. They seemed to be already okay except hairline slit in the ejector nozzle which was spraying unevenly, but now spray fine (did not mess with it. Just soaked it in cleaner until it was spraying through it evenly)
    3) I did, however, remove the nozzle tip from the ejector tube in order to clean it and then put it back on. It doesn't have thread or anything but does seem to fit on pretty snuggly. Can't imagine that it popped off inside.
    4) did not change throat plate and rod because I did not want take off the whole carb and there did not seem to be anything wrong with them
    5) did add a cleanable in-line fuel filter before the carb
    Last edited by imsoevil; 07-11-2019 at 02:10 AM.

  2. #2
    Administrator AdminSenior Member Wide's Avatar
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    Do you have a small vacuum leak anywhere? That would cause it and I found most likely suspect
    Smoke testing is the best way to tell
    .-/c-.,_ /
    (_)'==(_)

    "Logic will get you from A to B. Imagination will take you everywhere"

  3. #3
    Junior Member Just broke my cherry!
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    Quote Originally Posted by Wide View Post
    Do you have a small vacuum leak anywhere? That would cause it and I found most likely suspect
    Smoke testing is the best way to tell

    thanks. Looking at some videos right now and how to do that.will post what I found

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    Quote Originally Posted by Wide View Post
    Do you have a small vacuum leak anywhere? That would cause it and I found most likely suspect
    Smoke testing is the best way to tell
    All the videos I could find about smoke testing are about cars, not bikes. And I could not think of where I might disconnect the hose to blow smoke into.
    But there are plenty of videos on how to do it on a bike using starter fluid spray or propane. I tried it with propane and noticed no difference regardless of any of the spots I tried to blow propane into like around the hoses and also any places where I opened the carb during the rebuild. Not even when I took off the air filter and blue propane directly into the intake.
    Still revs around 3K or 4K RPM

    Can's say I'm surprised because I didn't actually mess with any of the vacuum hoses during the rebuild, so I don't see why anything would have changed.

    One question, though: how far is the idle mixture adjustment screw supposed to be able to go in?
    I have the version that has threads going all the way and no O-ring. But it only screws then maybe a little bit less than half way before feeling like it came to a stop and I don't want to force it.
    Are you supposed to be able to screw it all the way in until you see no thread before it comes to a full stop?

    Another possible hint: when I started with the choke open and then push the choke down about halfway the RPM slows down just a bit, as expected. But when I lower it even farther all the way down, it actually speeds up again, at least when the engine is cold. Don't know if that's a clue.

  5. #5
    Administrator AdminSenior Member Wide's Avatar
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    put screw all the way in and out 1.5 turns will get you ballpark
    Leaking intake gasket also may do it or if the mixture screw dont do anything you just may be way off on jet size. Lots folks over jet them without a dyno or some sort of wideband 02 to read what the actual mixture is

    Hope this helps
    .-/c-.,_ /
    (_)'==(_)

    "Logic will get you from A to B. Imagination will take you everywhere"

  6. #6
    Junior Member Just broke my cherry!
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    [QUOTE=Wide;577507]put screw all the way in and out 1.5 turns will get you ballpark

    Yes, I know that. What I'm asking is how far in is this crew supposed to be able to go before it is all the way in? Is it supposed to be able to go in all the way to the end of the thread before you turn back that one and a half turns? Is it supposed to be to the end of the thread or only about half of it?


    [QUOTE=Wide;577507] Leaking intake gasket also may do it or if the mixture screw dont do anything you just may be way off on jet size. Lots folks over jet them without a dyno or some sort of wideband 02 to read what the actual mixture is


    I wondered about the jet too. I did not change it and it was raining fine before I had to do the rebuild.
    But as I mentioned the accelerator pump diaphragm was torn and I think it has been for some time judging from the way it accelerated. It's possible the previous owner put in a bigger/smaller jet trying to compensate for it or something like that. What is the standard size jet that usually comes with it?
    I'm in San Diego, so we are at sea level.

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