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Idle Mix Plugs Stuck

Discussion in 'The Garage' started by Italianzero, Aug 16, 2020.

  1. Italianzero

    Italianzero XS400 Member

    Greetings all, I’ve been unsuccessful in the drilling method of removing the factory idle mix plugs despite reading all the forum commentary and miscellaneous guides out there.

    On the #1 carb it actually sank a bit deeper, and on the #2 the screw to pull it out just won’t bite strongly enough.

    Any advice short of going to a machine shop?

    Attached Files:

  2. amc49

    amc49 XS400 Junkie

    If that's where you are at now you simply haven't gone far enough, I'd have those out in seconds. That type plug is so lightly in place it's not funny.

    Of course, individual skills fit in there doing the work.
  3. Italianzero

    Italianzero XS400 Member

    Update: multiple drill bits and screws later and I was finally able to get the plugs out. The settings were very strange though...#1 was 1.5 and #2 was 2.6. The screws don't seem to be loose. Anything I should be double checking?
  4. xschris

    xschris XS400 Guru Top Contributor

    Yes, those can be very hard to remove. I have done dozens on xs400 carbs and xs650 carbs. In rare cases they do pop out. I use ever increasingly larger drill bits till all that is left is a tiny ring. Some people use a sheet metal screw then pry it out. I have seen the aluminum carb body snap from pressure so I avoid doing this. Make sure the hole is clear from metal bits. I put a little oil in the hole then screw the mix screws till they lightly seat. Clean and oil the hole again then back the screws all the way out. You should find a spring, washer and o-ring at the end. The o-rings get stuck in the bottom so take care getting them out.
  5. amc49

    amc49 XS400 Junkie


    Man I yank that same plug type and size all day long on other carbs with never an issue ever. But then I've yanked a thousand freeze plugs on engine blocks and heads too.

    With both mixture screws LIGHTLY bottomed then flip carb bank to look inside the front bores to see how far the mixture screw tips extend into the bore if they do at all. It can be a big indicator of how hard somebody has bottomed them out. Both if showing should be close to the same amount sticking out.

    The problem can be one of not knowing if you need to set both the same or not, normal is yes but if one has been driven in to damage the seat then the normal 'turn them in to bottom then back out X amount' may be wrong, the damage may damage the seat to where that is no longer correct. The seat flow area being now messed up to tilt the flow amount. Sometimes enough to mess up carb sync, one cylinder seems to be off when dead even.
  6. amc49

    amc49 XS400 Junkie

    On the two screws being different setting, one could have vibrated to slowly move or somebody could have actually preset idle HC or CO by a gas reader to make sure emissions were hit then they plug the holes. You never know. New engines are never fully carbon coated and I've found you can often alter the needle settings a bit to make an engine idle much better after 2-3 hours of engine running. I remember my brand new DOHC 750 beginning to idle lopsided after a few hours of use, I defeated the idle limiter screws on that one and then readjusted to a perfect idle that then stayed that way.

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