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Discussion in 'The Garage' started by Scotty4, Aug 15, 2020.

  1. Scotty4

    Scotty4 XS400 Member

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    Update. Put in the oem plugs it calls for in the manual, check out everything else and its looking okay. I moved the needle clips to the 4th notch but the upper not lower. It ran worse but did kick over way easier. Put the clip on the 4th from top and got it going again.

    Took it for a spin and it hits redline but with a lean surge at 4-6k then takes of like a top after that. It also died twice at idle once warm. 75mph is max at 7k rpm or so in 6th.

    My idle does seem a tad low after I reset the sync. Tank vent and idle adjustment? I'm at 2.5 turns out on both.

    Still amazed at how nice the bike sounds and how well it handles.
     
    motoTrooper likes this.
  2. ATXSOUTHAUSTIN

    ATXSOUTHAUSTIN ATXSOUTHAUSTIN

    There's another knob/screw under the throttle shaft (SOHC) that controls idle only. It's a flathead screwdriver on the DOHC, and on the side.
    Almost there!!
     
  3. Scotty4

    Scotty4 XS400 Member

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    @ATXSOUTHAUSTIN so there is one idle mixture screw on each carb, engine side. Onw big knib for idle, and the sync screw in the middle. Where is the other???
     
  4. ATXSOUTHAUSTIN

    ATXSOUTHAUSTIN ATXSOUTHAUSTIN

    Scotty!


    Ooohhh. The idle knob? It controls both carbs. Is that what you meant? That knob will be the last thing you adjust to get your idle right after you dial in the mixture screws? Where are you starting them? Try 2.5 turns out after lightly seating.
     
    Last edited: Sep 20, 2020
  5. ATXSOUTHAUSTIN

    ATXSOUTHAUSTIN ATXSOUTHAUSTIN

    You should look at a diagram whenever you get a chance. I know it can be intimidating, but someday you'll be giving advice. Until you take it off and apart for the first time, a picture is worth....
     
  6. Scotty4

    Scotty4 XS400 Member

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    Ive had tbe carb off and apart more times tha I count. Only recently did I start to understand how it worked. Before was just to clean as I had no clue (like 10 years ago). I set both to 2.5 and blocked both 1st holes halfway with the butterflies then synced on the bike at idle, then up to 5k and allowing it to drop.

    My idle is 1200 but that changes as I adjust the sync so I am fiddling with both. The rpms hang which I read was too much air so tried 3 and even 4 turns out but its just not coming out of it. I have a new set of points for it incase so will see how they look and my need to time it.
     
  7. ATXSOUTHAUSTIN

    ATXSOUTHAUSTIN ATXSOUTHAUSTIN

    Sorry, didn't know you had them apart I guess I meant separated, but I see you've synched them. I totally understand what your saying about understanding. Can be confusing at first. Have you sprayed wd-40 around the boots?
     
    Last edited: Sep 20, 2020
  8. ATXSOUTHAUSTIN

    ATXSOUTHAUSTIN ATXSOUTHAUSTIN

    Don't know if you've tried this, but make sure the throttle cable isn't binding on anything, too. Even move it around while moving the handlebars. You're doing everything right; it won't be long. Make sure the boots are tight. Spitballing here.

    Do you have a manometer? If you put your hands behind the pipes, feel the pressure to see if it feels the same, or 9nes pushing harder.
     
  9. Scotty4

    Scotty4 XS400 Member

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    I will check the cable. Thanks. I sprayed with carb cleaner around the boots while running and got nothing. Boots seem tight but I will check. And I made a manometer to sync, just two bottles with ATF in them. When I got it fired first, the left was pushing harder, now its the right. But only slightly.
     
  10. ATXSOUTHAUSTIN

    ATXSOUTHAUSTIN ATXSOUTHAUSTIN

    Good job, man. You are so close! Yes slightly is ok. You will need to do it again when it is fully warm after a 20 minute ride to hone her in. Some of the earlier bikes are different; I think you should try turning the mixture screws clockwise to richen the mixture. Or begin by going for the highest idle with the mixture screws, then I go back slightly. then the other side. Now use the idle knob to lower RPMs. Something ez to check.
    Make sure there's a vacuum line to your petcock or plugged....... I'm sure you did this when synching. oOhhhhh.....You may need a new o ring for your mixture needles. Mike's has em
    Let me know and good luck!
     
    Last edited: Sep 21, 2020
    Scotty4 likes this.
  11. ATXSOUTHAUSTIN

    ATXSOUTHAUSTIN ATXSOUTHAUSTIN

    Check the cable while moving it around, too.
     
    Last edited: Sep 21, 2020
    Scotty4 likes this.
  12. xschris

    xschris a lifestyle not a trend Top Contributor

    Pre 80 bikes use a different style of carbs. No o-rings with them. Make sure you pilot mix screws tips have not broken off in the carb bodies. This is a very common thing on the 77-79 carbs.
     
    Scotty4 likes this.
  13. Scotty4

    Scotty4 XS400 Member

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    Would I tell this by taking the screw out fully? I have not tightned them further than feeling a kiss of tension.
     
  14. Scotty4

    Scotty4 XS400 Member

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    The vacuum line is definitely there. Made that mistake with my buddy's KLR and I will never forget!

    Could the cable be sticking due to age? WD40 work for lube or what is recommended? Graphite?
     
  15. xschris

    xschris a lifestyle not a trend Top Contributor

    I use cable lube for cables. But any regular oil would do. The tips are easy to break. Could have happened before you. I would pull them out and post pics. A look down the hole with the carb off would tell for sure.
     
    Scotty4 likes this.
  16. ATXSOUTHAUSTIN

    ATXSOUTHAUSTIN ATXSOUTHAUSTIN

    Xschris, do the pre 80 bikes also turn the mixture screws in the opposite direction? Never owned one before 80. Still learning every day. Also, could he be missing a washer?
    Long shot, but bikes can run lean with low fuel in the bowls. Not lean enough for this condition. I don't think it's float height, but I'm brainstorming here.

    Scotty4, If you used the manometer you should have tapped into the same fitting used for the petcock(also one on the other side) Double check that line isn't sucking air on the other end of the petcock line. When you said one was slightly more than the other I thought you meant ATF...... the exhaust should be even pressure on both sides. The manometer checks this via vacuum pressure.



    Yes, just unscrew them all the way out. Count the turns and seat them lightly so you know where you were.
     
    Scotty4 likes this.
  17. xschris

    xschris a lifestyle not a trend Top Contributor

    Turning them out for richer. 77-79 just uses large spring and needle. Nothing like the 80-82 bikes. Float height will greatly effect tuning.
     
    Scotty4 likes this.
  18. amc49

    amc49 XS400 Addict

    If the mixture (fuel + air) screws are between the carb slide and engine then they richen going counterclockwise. If they are between slide and back of carb then they are not mixture screws but air only and counterclockwise is going leaner.
     
    Scotty4 likes this.
  19. Scotty4

    Scotty4 XS400 Member

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    I may get a new rubber cap for the left side and a new line for the right to petcock. Just want to rule that out.
     
  20. ATXSOUTHAUSTIN

    ATXSOUTHAUSTIN ATXSOUTHAUSTIN

    Thanks amc. It's all coming back now. If they're behind the slides they obviously aren't getting fuel. The air only screws are commonly referred to as mixture screws despite the fact, just to confuse people...... Or is it so people don't get confused..... Things that make you go hmmmmmmmmmmm?
     

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