Forums 🚥 PIT STOP 🔧 Hyosung Technical Help Performance gains ! Gt125rc

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    • #6610
      Carter
      Member
      • Topics: 6
      • Replies: 17
      Joined:
      Aug 20, 2021
      @carter69
      Llanelli
      GT125R
      • Ok so I have a few queries for the enthusiasts .. I have so far done k&n intake & rejetted, aftermarket performance end can, iridium plugs, heavy duty clutch overhaul now I’m am planning to make a custom stainless 2×1.5″-1×2″ pipe and a full top end overhaul Including opening the ports and polishing exhaust port polishing and reseating the valves and honing the cylinder bore however to do this I assume I will nide tighrbore piston rings and maybe slightly bigger pistons does anyone know of any rings or pistons from any other engine that might work or anywhere that does oversized pistons and rings for this engine and what is the standard compression pressure in this engine
    • #6618
      ♠️ MARCEL
      Administrator
      • Topics: 38
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      Joined:
      Aug 20, 2021
      @mf448kxn6
      North UK
      GTR

      Hey,
      Are the plugs “IX”  or “IA (Real LASER)”  –  I say this because Hyosung 125s don’t enjoy IX plugs for that long.   It’s the LASER or  stock CR8E are what they like most.

      Have you had a chance to browse around the shop section as what’s on there is what many of the registered folk on here use , and to the extremes they do eventually see 90 indicated on the dash.

      Humbly speaking as a wizard, it is a little overkill to try to mess with the valve heads or boring the cylinders out.   However there is no aftermarket oversized pistons for the vtwin , as i don’t think the crank wants to deal with a big bore kit  (like you see on the Yammy 125s). It’s actually not a bad engine to be fair as it is,  it’s only the weight of the bike that lets it down on the initial take off but it will defo hold down long stretches on the M or A roads better than punny little single cylinder 125s.  Believe i’ve pushed the donor 125 all the way up & down the country on the M1 & M62 , i was pretty surprised coming from a guy who only had a ZZR400 that did 120 at best! and ofcourse the GS500 i recently sold.
      90 is good for the hyo. However, i do like your bravery to go to the dark side , not many of us actually hone the cylinders or mess with the valve heads.
      You may get yourself custom made titanium valve springs for the cams.  No aftermarket folk do this for Hyosung 125s, so totally a custom job here.

       

      2 pipes (rear and front) joining to 1 pipe to the end can, seems to pull best on 125s with a long exhaust can that has a baffle hole of the size of 10p. I tried a few configurations before.   If doing dual exhausts,  that will look really good i won’t lie , just be sure the cans are full size with a small baffle hole so it isn’t loosing out too much puff out there.  It’s not a 2 stroke , but you’ll be surprised the 4t pulls more with a baffle in than out.

      I did make 2 tutorials on the site for carb jetting and the slide mod which you can check out as you browse deeper in the forum

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

    • #6623
      Carter
      Member
      • Topics: 6
      • Replies: 17
      Joined:
      Aug 20, 2021
      @carter69
      Llanelli
      GT125R

      I have purchased a fair bit from you lol intake jets ss bolt set clutch ect I basically know your shop like back of my hand ahaha and yes I have had 93 out of it so far and I have manager to get it to run with no dead spots when warm some how lol I have already rejetted carbs ect the exhaust I built will be a 2into1 the can I have is not a full size one but is a fairly decent can gives of a lovely sound and a massive step up from standard one lol.. however I do believe with porting polishing and just polishing the cylinder with a hone and my custom exhaust and play with the timing and gearing a little I do believe it will do 100mph+ I have managed to reliably get around 85 out of 125 singles and when I jumped on the R it just felt like a different level right from the off for a 125 it was like being on a restricted 600 I had 90 the day I got it although it I brought it knowing it had a bottom end knock turned out the Conrod bearing had gone and piston came down further and smashed the fins off the rear piston that extra bit of stroke was what got me 90mph standard which lead to rebuilding everything and saw the potential in that engine

    • #6624
      Carter
      Member
      • Topics: 6
      • Replies: 17
      Joined:
      Aug 20, 2021
      @carter69
      Llanelli
      GT125R

      And IX I didn’t know there were others for this bike lol

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