Forums 🚥 PiT STOP 🔧 Hyosung Technical Help GV125S-EFI Only sparking on 1 cylinder

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    • #8877
      Lee
      Member
      • Topics: 4
      • Replies: 10
      @gibsondude78
      NE Lincs
      GV125S

      Hi guys,

      Back at the beginning of september I got caught in quite a heavy rain storm whilst riding home early hours in the morning from work. I made it home ok, but my bike started to feel a bit groggy. I left it to dry out under cover for the weekend and then I was back at work for 4pm on the monday. I started the bike up but it sounded a little off, not the usual purr… Whilst sat on the bike I pulled the HT cable from the front cylinder to see if the engine noise dipped… It did… I put the lead back on and the engine picked up again… I did the same to the rear cylinder… Engine dipped… Put the lead back on… Nothing… Engine sounded the same with or without the rear lead connected… I shut off the bike and left it a few minutes, pulled the front HT lead off and left the rear on and then tried to start the bike… Nothing… Just kept trying to turn over…

      I initially though I’d damaged the spark plug or lead somehow, so I drove over to halfords and picked up a couple of NGK iridium plugs and whipped home and replaced them… Still nothing from the rear… So I went online and bought a replacement coil pack thinking this might sort the issue out… After 6 weeks of waiting for the delivery the coil finally arrived and I swiftly fitted it to the bike… Still f*****g nothing!… I even tried to swap the old rear coil with the front coil… Nothing happening from the rear cylinder but the front one worked fine with the rear coil?!

      By this point I was ready to find a big open field and a rather large jerry can! I called the dealer where I bought the bike from, and as luck would have it… My warrenty had expired on the 9th of september… But they said they’d have a look at it for me anyway… for a cost… Hmm, yeah… Think thats gonna be a last resort!

      Any ideas what else could be causing the no spark issue?

      Any help would be highly appreciated!

       

      *Edit*

      I forgot to mention, the rear coil gets very, very hot to touch whilst the bike is running, so it’s obviously getting a charge…

    • #8878
      ♠️ MARCEL
      Admin
      • Topics: 44
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      @mf448kxn6
      North UK
      GTR

      Hello Lee,

      Welcome to the site! Please do not panic and set the bike on fire. I totally understand the frustration believe me i do! It is a lovely bike to be fair but, there is a general consensus that hyosungs can act strange after a blizzard of a rain situation if you notice:

      – Water getting to the HT caps
      – Water getting to the plug holes (older models that had missing dust covers by previous keepers taking them off)
      – Water getting to the air filter, regulator plugs , and such.

      Korea did mitigate ways to avoid this happening but it can happen to other motorcycles though, so don’t worry your situation is easily fixable i guarantee it.

      Hyosung 125’s dont really like “IX Iridium” plugs (the blue box) because they are overhyped junk. They are really good then they wane fast, after they wane, they don’t produce their peak power anymore.

      So for spark plugs, it is advised to use “Laser Platinums”
      See below

      NGK LASER Iridium Spark Plugs x2 – Hyosung GV125-S (Injected)

      These plugs can even last you 2yrs (unlimited miles) if taken care of (meaning the electric system must not give them a reason to give up the ghost, like any plug would or bad fueling system) However, the throttle based on feedback i get from other GV125-S owners is that there is no speed gains but the bike starts faster and throttle feels sharper.

      Next up, which is 100000000% recommended to all GV125-S owners is to use an HT Cap with a race lead attached to it.
      See product details below for deeper explanation
      And also study pictures please, because it shows that the owners “KEEP” the rubber dust caps that go to the coil itself. to stop water getting in between.

      NGK Uprated HT Lead Spark Plug Caps (x2) – Hyosung GV125-S EFi (Injected Models from 2020)

      Also NGK products for HT Caps rarely fail. Hyosung’s black caps are likely made in china. (as was the case with older bikes having HT caps made in china and they failed a lot in various ways, not just because of weather, heat was their enemy too)

      Now speaking of heat, can you share the picture of the coil you purchased? was it genuine?

      If you swap coils, does the back coil still get hot again ?

      Lastly, as it’s important — Get a meter, check the battery is 14.5v at idling and 15V max around 5k revs.

      Go under the bike, take a picture of the regulator/rectifier. If it has a part number printed on it. Copy it.
      Also follow its plug under the seat, get a photo and show me.

      I may see about stocking up a better regulator for these bikes like i already do for the 650, 250s on the shop and the older “carb models” of 125cc , with good success. It has been an old consensus

      Keep us posted

      You got this!

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

    • #8884
      Lee
      Member
      • Topics: 4
      • Replies: 10
      @gibsondude78
      NE Lincs
      GV125S

      Thanks for the reply Marcel,

      My brother-in-law has just been to have a look at it, he’s a car mechanic with little experience working on bikes, he thinks it could be the Stator?

      I’m guessing I’m going to struggle finding a new one that fits a ’21 plate 😥

    • #8885
      ♠️ MARCEL
      Admin
      • Topics: 44
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      @mf448kxn6
      North UK
      GTR

      The stator will be fine as it will be too young to have issues at this rate,  if the stator was failing, the bike simply would not start whatsoever.
      Also it will not produce any power to the regulator to feed 14V to the bike.

      Stator is multi purpose
      – EFi Pulse Sensor will tell the ECU that it’s okay to start running and the ECU is constantly communicating with the Pulse Sensor of the stator.
      – Charging Element – the second part of the stator will be sending AC power to the regulator so it makes DC power for battery (charge) & electronics  (general running)

      Your bike dropping 1 cylinder will be most likely what has been on my previous comments 🙂 ,    Your bike is too young right now to have a fried stator.

      Though, the stator may still be working fine, i’d treat it to a better regulator incase the current regulator is fishy as was the case with older hyosungs.

      Infact he can test the stator himself now for his own peace of mind.
      1. Bike stays off. Do not turn on the dash either.
      2. Get a meter and set it to 400 ohms max. or 200 ohms max.  (not 200K / 200,000)
      3.  Grab the stator’s “2-Pin” plug,  and probe it.  Both meter leads inside it.   = Get ohms reading and tells us on the forum what it says and ill confirm it’s okay or not.

      4. Part 2……….
      See the “3 Pin” Yellow Plug for the stator ,  right then, do it like this exactly.

      A.  Meter wires inside Pin 1 & Pin 2  (any order) = Get ohms.
      B. Meter wires inside Pin 2 & Pin 3 (any order) = Get ohms.
      C. Pin 3 and Pin 1 = Get ohms.

      Let us know also what A.B.C says

      It’s 2 stage test  (since it has 2 plugs one with 2pins and one with 3 pins)

      There is no need to ground the frame or anything, this is how Korea does it also

      How much voltage is the stator making ? It would be best to try get both cylinders sparking first as you wouldn’t want a back cylinder getting fuel but no spark, eventually the piston rings will get funny  or the engine may get hydrolocked when fuel & oil start mixing and filling up at the back pot.

      Regards.

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

    • #8887
      Lee
      Member
      • Topics: 4
      • Replies: 10
      @gibsondude78
      NE Lincs
      GV125S

      Ok, I’ve just popped down and took some readings with my multimeter set to 200ohm.

      So, assuming I got the correct plugs (I left them plugged in is that right?), Part 1 test (Blue and Green wires): 106.6

      Part 2 test: A: 00.8, B: 00.8, C: 00.8

      Also, I can’t seem to locate the regulator/rectifier… If I’m honest, I’m not quite sure what I’m supposed to be looking for… My bro-in-law doesn’t either 😕

    • #8888
      Lee
      Member
      • Topics: 4
      • Replies: 10
      @gibsondude78
      NE Lincs
      GV125S

      *EDIT* Also, I can’t seem to locate the regulator/rectifier… If I’m honest, I’m not quite sure what I’m supposed to be looking for… My bro-in-law doesn’t either 😕

      My bad, found it… Is there a test to see if the rectifier is at fault?

    • #8890
      Simon
      Member
      • Topics: 1
      • Replies: 219
      @syco
      Kent
      Gt250 f1

      Look up on YouTube it’s quite simple as they are diodes & should only allow one way travel

    • #8893
      ♠️ MARCEL
      Admin
      • Topics: 44
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      @mf448kxn6
      North UK
      GTR

      Get a picture of the regulator itself,  and copy any part numbers written to it.   And also post a second picture showing us what the plugs look like.

      The regulator will say 14v idling  (both cylinders need to fire first though so engine runs properly)  and 15v max around 15k revs at the battery terminals.

      If the reg is good, wonderful.   Consider pimping the unit later on. I will know what to get based on what visuals you send me on here.

      Stator tests = Your stator is fine. It’s too healthy to worry about it now.

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

    • #8899
      Lee
      Member
      • Topics: 4
      • Replies: 10
      @gibsondude78
      NE Lincs
      GV125S

      Get a picture of the regulator itself, and copy any part numbers written to it. And also post a second picture showing us what the plugs look like. The regulator will say 14v idling (both cylinders need to fire first though so engine runs properly) and 15v max around 15k revs at the battery terminals. If the reg is good, wonderful. Consider pimping the unit later on. I will know what to get based on what visuals you send me on here. Stator tests = Your stator is fine. It’s too healthy to worry about it now.

      The plug on the left is from the rear cylinder

    • #8902
      ♠️ MARCEL
      Admin
      • Topics: 44
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      @mf448kxn6
      North UK
      GTR

      Yup, as per previous comments. NGK HT caps we have will be your savior, and defo marry them with laser plugs. She will be happy afterwards for sure.
      I would not buy the IX ones again to be honest nor use the OEM caps. You’re amongst the many owners who have had to replace the caps and use laser plugs , after that, the coils generally spark good. Infact , if the fuel system stays healthy and the electrics behave, you will keep the same laser plugs for 2yrs. I have personally gone three years without changing plugs.  Usually when a customer drops their bike off to me, first thing i do is get rid of the caps & waterproof the overal electric system a little more.   If the OEM coils are good, i leave them alone , unless i change them at the same time as replacing caps and fitting new laser plugs.       However,  even stock CR8E will do a better job than CR8EIX on the 125cc,   just that CR Lasers burn fuel better, so that helps in winter making the 125s start sooner and warm up their cylinders quicker, the throttle is a little sharper when married with the ngk caps.  the 250’s can live on stock CR8E and usually warm up a little faster anyways.

      I wont lie , the right side plug looks kinda sooty sooty.   It should about dark brown in the middle.

      The threads on the side of the plug should have about 3 to 4 lines dark and the rest clear . This suggests you could invest in Motul Factory Line Coolant,   (Best one there is and i like motul products, so i may sound biased but that’s all i trust with my bikes)  , this may help cool down the bike a little better than whatever the dealer put inside   (not all Hyosung GV125-S efi come to UK complete, some are usually in a crate that a dealer probably has to put liquids in ,  battery and fit handle bars, etc things removed to fit the bike in crate boxes and inspection checks before selling it to customer, some dealers can vary their methods of doing things – In either case, if warranty is enforced, they would make sure the bike is sound before selling to you with paperwork etc.)

      Thank you, and don’t worry i will sort out a better unit for you.    Remember to check batter voltage idling and revving to 5k when both cylinders spark.

      By the way, any chance you can show me the regulator connector plugs ?  I build  plug & play terminals for upgrade regulators

      Like this example  below

      Upgrade Regulator Rectifier {Reg Rec} :: EFi Hyosung GV250 GT250R GT250

      As long as i can see the regulator connector plugs i will know what to do! 👍

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

    • #9060
      Lee
      Member
      • Topics: 4
      • Replies: 10
      @gibsondude78
      NE Lincs
      GV125S

      Just thought I’d post an update on my problem…

      I managed to find a complete wiring harnass for my bike (same year and similar milage) on eBay for £80, so thought I’d take a punt on it…

      It came with the ECU, both coils, the rectifier, fuse box and all of the relays… My thoughts were to swap out bits piece by piece to see if I could narrow down where the problem lied…

      I started with the ECU as it was the most accessable part at the time (I already had the old unit disconnected from my old harnass)… And f**k me, the bike turned over straight away with both cylinders purring like a mofo!… I nearly did a little sex wee when I heard that familiar growl…

      Just to make sure, I reconnected my old ECU, and sure as damn it the ol’ girl sounded like a wet fart after a night on Guinness!… Popped the new ECU back in… Purrrrrrrrrrrrrrrr… B-E-A-Utiful!!!

      So, I’m guessing I fried the old ECU somehow when I pulled the HT-Lead months ago…

      It’s been 2 days now, and I’ve done around 150 miles and she still sounds as sexy as she did the day I took ownership.

      Atleast now I have a few spares just in case anything else decides to give up the ghost.

       

    • #9062
      ♠️ MARCEL
      Admin
      • Topics: 44
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      @mf448kxn6
      North UK
      GTR

      That is amazing news , i am very happy for you!

      Don’t throw away anything, trust me, with EFi parts, you need all the spares you can keep and she will be with you for years to come.

      If you go somewhere nice,  share some pics onthe forum 😉

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

    • #9070
      undocab
      Member
      • Topics: 0
      • Replies: 4
      @undocab
      USA
      2012 GT 650

      I am %99 sure your first problem was just a spark plug cap.

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