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Hyosung GV125 C

Well done , you’re getting there. 👍 So i will break down the plugs in simplest terms so you know what to expect (Get a fresh set of CR8E x 4 of them) part of this process is unfortunately called “Plug Chopping” , gotta go through a set of plugs until she is happy, as old plugs wane fast and dont behave the same if they dont work well (“Fouled up”) . Your plugs:

  • “Dark Black Ring” = Rich Idling / Low air / Dodgy mixture (i hope not) / Pilot Jets too big / Ignition Coil + HT Cap (easy fix) / Choke used during startup or while riding etc… (choke enriches the carb) _________ Ideal colour = English brown tree trunk / Milk Chocolate / Brown Leather Boots = I know, but best way i can describe a ideal shades of brown or “Tanned Grey with Brown Tinge” ==> Means starts should generally be easy in icy days or not even needing a choke. _________
  • “White Pure Center” = Main Jets Blocked / Slide Needle is wrongly put to the lean setting / Air Leak at high revs / Low fuel flow at high revs / Main Jets too smll / ______ Ideal Colour = As above ^ . White is never a good sign because it would mean there is very little fuel at while riding and bike is going to overheat faster , the oil in the bike breaks down hard (sooty black oil much sooner) , plug breaks down , holes in piston may burn one day , compression loss due to piston rings cooking in extra heat, and so on, i believe you will get the gist of where we are going with this. We would rather a dark center than a white one , at least “slightly” rich MAIN JETS or SLIDES means high speeds help the bike cool a tiny bit on each intake cycle , as petrol has a tiny cooling effect (tiny) (Another reason GTR bikes for Hyosungs have bigger jets at rear than the front due to the fact, it gets less air flow to it hiding under the plastics , plus the front engine is in the way , just how v-twins are.)

I hope this made any sense ? Let us know your test for electronic sparking coils later on, take your time, it’s a stormy week anyways.

hello again ,


weather looked not to bad today so I have managed to do some measuring for you please see attached photos ,

Front cap ,

rear cap

both coils shown 0.6 


hope I did this right ,

thank you again for all of your assistance