Forums 🚥 PIT STOP 🔧 Hyosung Technical Help GV125 Running on 1 Cylinder at Idle

  • This topic has 4 replies, 4 voices, and was last updated 1 week ago by DAVID.
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    • #6346
      Moustache Man
      Member
      • Topics: 7
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      Jan 14, 2020
      @benjaminsmith
      Colchester
      GV125 2016

      Been starting to notice this whilst the bike has been idling, and whilst waiting at traffic lights.

      I understand that these bikes do not have the “iconic” V-twin sound, but you can easily distinguish between a single and a twin.

      Whilst the bike is at low RPM, it sounds like it is only running on one cylinder. I don’t know what could cause this, blocked carbs? Sooty plugs? Low power from the battery? Is this a common fault?

      The second I pull away, it chugs and jerks a bit, then I can hear the second cylinder fire up and it runs smooth again. Another reason to add to my list of “love-hate” things about my bike haha. I don’t want a new relationship, I want a long-term marriage, with little commitment or effort required!!

      Would anyone know any easy ways to fix this? I’m no mechanical genius, but I have a decent knowledge and some handy tools.

    • #6357
      Tom
      Member
      • Topics: 2
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      Jan 14, 2020
      @kernow
      Cornwall
      GV125

      I am no expert either but I would check these. Because bad cylinder fires up when you increase throttle I would not think it is piston or rings.  But I would check compression anyway. My gut says fuel or spark.

      Pull sparks and look at colour and put new ones in.

      See if you have spark on the bad cylinder by removing both and grounding tips against engine (bare metal) and turning over engine.

      I would also check battery voltage when engine off (12.4v ish) and then check voltage with engine at high idle 1800rpm (14v +). Might not have enough electrical juice at idle, but spark test will show that.

      If you have no spark then test coils. An easy check just swap them over (literally swap them not just leads to spark plug) and see if fault follows coil. If it does it could just be the lead or cap You can often solve that by removing cap from lead, chopping a 1cm off lead and replacing cap on lead.

      Doubt it is rectifier as one cylinder is good.

      If spark good then I would look to fuel.

      Doubt it is fuel lines or pump as fires up fine with throttle. Pilot jet on bad cylinder or float blocked. Just give it a good clean.

      A split or cracked intake can also mess up idle, spray carb cleaner (combustable type) on inlet rubbers when idling and see if that makes her fire.

      After that I would start scratching my head.  Hopefully Marcel sees your post and can solve this one.

      Good luck and tell us how you get on.

    • #6368
      Moustache Man
      Member
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      Jan 14, 2020
      @benjaminsmith
      Colchester
      GV125 2016

      Cheers Tom, that is super helpful. I shall find a couple hours tomorrow to run those checks, I think I have a spark plug socket that will fit.

    • #6372
      Carter
      Member
      • Topics: 0
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      Jan 14, 2020
      @carter69
      Llanelli
      GT125R

      Been starting to notice this whilst the bike has been idling, and whilst waiting at traffic lights. I understand that these bikes do not have the “iconic” V-twin sound, but you can easily distinguish between a single and a twin. Whilst the bike is at low RPM, it sounds like it is only running on one cylinder. I don’t know what could cause this, blocked carbs? Sooty plugs? Low power from the battery? Is this a common fault? The second I pull away, it chugs and jerks a bit, then I can hear the second cylinder fire up and it runs smooth again. Another reason to add to my list of “love-hate” things about my bike haha. I don’t want a new relationship, I want a long-term marriage, with little commitment or effort required!! Would anyone know any easy ways to fix this? I’m no mechanical genius, but I have a decent knowledge and some handy tools.

      first just start the bike up and don’t revs it let it warm up feel if both the cylinders are getting hot.. If only one your prediction is correct and is caused by either intake spark or compression so I’d start with compression test of all is good swap the plugs over if that cylinder still isn’t firing you should check intake manifold for cracks splits if that’s good clean your carb especially the pilot jet if it’s still not firing on idle your idle mixture is wrong on the carb going to that cylinder

    • #6374
      DAVID
      Member
      • Topics: 3
      • Replies: 15
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      Jan 14, 2020
      @bowie
      norwich
      GT 125R AQUILA

      Also never ever put in E10 fuel, into your bike,

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