Forums 🚥 PIT STOP 🔧 Hyosung Technical Help Hyosung 125cc gv running slow when warm

This topic contains 4 replies, has 2 voices, and was last updated by  Trevor 1 year ago.

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  • #1202

    ♠️ MARCEL
    Administrator
    • Topics: 32
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    Joined:
    Apr 30, 2018
    @mf448kxn6
    Location:
    North UK
    Riding:
    GTR
    Points: 2,710

    This question was asked before on the facebook group,  so what i would say is this:

    Idle Speed.
    When the bike is warming up, set the idle to 17500
    1550 is a bit weak in my opinion.

    Fuel system:
    – Change up to 8mm fuel lines = This lets more fuel in the pipes to the carbs, so it’s less likely to starve off at high speed runs.
    – Inspect your fuel filter , if it’s the factory small one.  Upgrade a large filter the size of 2 golf balls (size wise)

    Even though the large filter will last probably 20K miles, the extra weight & fuel helps with gravity assist (that means fuel drains down faster from tank)

    Standard grey lines on hyosungs last about 2yrs before needing to be changed,  braided lines last many years.

    Carburetors:
    If you can, remove the carburators off the bike,  then unscrew their “Float Bowls”
    – Unscrew 2x Skinny Pilot Jets  = They should be size 15 each & unclogged
    – Unscrew 2x Main Jets = They should be 87.5 x 87.5   (identical) & clean then.

    Put a jet up in the air  (away from the sunlight!). If it’s not clogged , your eyes will see a light through that hole.

    You can use Carb Cleaner to clean the carbs.

    Power tip = If you change your main jets to the following 90 Front & 90 Rear = This may use a bit extra fuel, but your bike will maintain top speeds much better.

    Also, before putting the carbs back on the bike,  put your fingers on the black-diagphragm slides.  Push them inside & they must “retract/bounce-back” quickly.

    If they get stuck at any point or are very slow to slide down.  You may have some dirt inside the diapgrhams.

    If screwdrivers fail, use mole grips and unscrew the TOP MUSHROOM COVERS of the carb  (x8 screws again).  Clean out the insides & make sure the diaphragm slides don’t have any particles clinged to them.

    Once the carbs are back on the bike, it should run much better here on , also with the aid of improving the rest of the fuel system.

    Your bike sounds starved a bit and isn’t getting what it needs at high gears

    =======

    Electrics

    At 3,000 RPM = Battery should say “MINIMUM” 14v =
    Any 13v readings means the regulator is probably gone, and wont cope with extra demands at high gear.   Idling the bike doesn’t cause much stress to it.
    Hyosung books state 14 – 15v as normal operating state.

    Coils
    1. Get a multi meter & switch to KILO OHMS
    2.  RED wire of your meter =  Inside the HT LEAD
    3.  Black wire of your meter = ON SPADE TERMINAL of the Coil
    4. It should say  5.0 – 6.2K Ohms  absolute maximum.  Any more, the coil is failing or may cause weird behavior when it gets warm.

    Battery
    12.8 Volts when it’s Off.

    I hope this helps ,  if you need extra help or pictures on anything , just let us know  & I’ll post them up on here!

    // Meditation doesn't mean you have to sit still....

  • #1203

    Trevor
    Member
    • Topics: 4
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    Joined:
    Apr 30, 2018
    @bigtrev1969
    Location:
    Lisburn
    Riding:
    Hiyosung Gv125 aquila
    Points: 198

    Many many thanks for all that info even tho im not very technical woth bikes. Will get someone to check carbs as havent a clue. Will renew plug leads to. I notice my battery dies after 2 days if i dont start the bike each day.

    Regards Trevor

  • #1215

    ♠️ MARCEL
    Administrator
    • Topics: 32
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    Joined:
    Apr 30, 2018
    @mf448kxn6
    Location:
    North UK
    Riding:
    GTR
    Points: 2,710

    What battery do you have ?

    Commonly it’s the regulator that fails and is the mother of the bike’s electrical system.

    Switch on the bike.  Switch your meter to DC Volts.  Rev up to 2000 – 3500 rpm

    You should see 14.6v at least.  The books for the GV engine state norminal running rate is 14 – 16v max.

    Any 13v readings? The regulator is probably gone.

    HT leads normally are ok & it’s insulator – Usually it’s the black coil itself, that goes out too.   If you ask me,  Coils & regulators are usually the biggest let downs on electrical side.

    As for your fueling side. A good carb clean is handy always.    I am going to publish an article that shows step-by-step  Jet Swapping & some extra info for owners looking to self-maintain their carbs.

    // Meditation doesn't mean you have to sit still....

  • #1216

    Trevor
    Member
    • Topics: 4
    • Replies: 9
    Joined:
    Apr 30, 2018
    @bigtrev1969
    Location:
    Lisburn
    Riding:
    Hiyosung Gv125 aquila
    Points: 198

    Many thanks for tge reply. Havent tested the battery but if i don’t start the bike for 2 days i need to charge the  attery as goes flat. Will try battery first and see if that helps. A real pain as i have the bike looking well after a guy ripped me off saying he had done everything. A found by by doing it all myself he hadnt as much as changd the plugs.

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