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xs400 dies on idle

Discussion in 'The Garage' started by Jaredg222, Mar 13, 2022.

  1. Jaredg222

    Jaredg222 XS400 Member

    Hey there. I just bought a 1981 xs400 Special. My first older bike. I have always had newer street bikes. So I'm pretty new to this. It ran ok when I bought it. The seller told me he rebuilt the carbs and went through the bike. It died on his way over to sell it to me. He brought it back home and fixed it. he said it was a connection on the battery. Anyways. it ran fine when I test drove it. So I bought it. Ran good the next day. Then the day after it would barley start and or idle correctly. I bought a new battery and plugs. Also replaced the fuses. Now it starts up no problem %90 the time. But the bike will only idle with full choke on. And when it does idle sometimes it will go high and stay at a high rpm. Wants to sputter and die out without full choke. I connected the battery to my truck battery and the bike runs pretty much perfect while connected to it. It idles perfect and will idle without choke. Would this mean I have an issue with the spark? I'm also considering it to be a vacuum leak somewhere. The left side plug looks black and the right side a brownish color. Also I'm in the process of messing with the mixture screws today to see if that helps. Thanks
     
  2. Jaredg222

    Jaredg222 XS400 Member

    OK. Messed with the mixture screws and throttle screw. I got it to idol now better. Still wants to die though without choke on. Sometimes will run for a few minutes fine without choke. Then will just stumble and die
     
  3. Jaredg222

    Jaredg222 XS400 Member

    Update. Got the bike to idol perfect pretty much and no dyeing at idol. When i ride the back it rides great other than low RPMs then it will want to or does die. I switched it to PRI and the bike runs perfect pretty much. Is it bad to ride the bike on pri? Do i need a new petcock?
     
  4. tstidham

    tstidham XS400 Addict

    Usually running only with choke on tells you it's a lean mixture. If everything inside the carbs is clean and flowing properly, keep enrichening the idle jet screws (turn them out) to increase idle speed and then drop the idle speed screw to keep the carbs off the main circuit. Once enrichening starts making the idle drop, turn them back in 1/4 to a 1/2 turn.
     
  5. Jaredg222

    Jaredg222 XS400 Member

    Since i got the carbs tuned in and messed with the idle screw the bike has been running great ever since
     
    tstidham likes this.
  6. Jaredg222

    Jaredg222 XS400 Member

    Also it needs the petcock always on as mentioned above to have it run correctly. Rode it about 2 hours 1 way the other day and 2 back with no issues
     
  7. Jaredg222

    Jaredg222 XS400 Member

    Also threw in a brand new Fuse block which helped it. The idle fuse was really not connecting perfect causing it to want to die sometimes
     
  8. Jaredg222

    Jaredg222 XS400 Member

    Only issues now i have with the bike is the blinkers stopped working after installing new bars on the bike
     
  9. JPaganel

    JPaganel XS400 Addict

    Are your bars painted? If so, there might be a ground issue.
     
  10. Jaredg222

    Jaredg222 XS400 Member

    They are. I did sand them down pretty good. but...maybe i do need to do a 2nd sand down on the blinker side. that is the the only thing I could think of. But my back brakes just snapped on me today after a long ride....the bolt that connects the assembly to the brake drum broke in half. most likely original. so blinkers will be after the brakes haha.
     
    JPaganel likes this.

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