Reply To: GV125S-EFI Only sparking on 1 cylinder
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!