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gt125r

New vs old gen Hyosung gt125r

Hi there,

I’m currently looking for the difference between the old gen Hyosung gt125r (with the old style fairings) compared to the newer models that have the new fairings and are fuel injected blah blah blah(also which one is easier to upgrade to go faster) . Is anyone able to help since I’ll probably be looking to buy one soon and want to know which one to get. Thanks

GT125R in Norway

Better late than … ever?  (Old farts can also have fun on 2 “small” wheels)

I’m Arne, born in the mid 60’s, learned about motorbikes 14-15 years old, “restored” some 50’s old wrecked bikes, before getting my licence, and buying a used 77-78′ Kawa KH-100ES.  And at 17, I got a 69/70′ Kawa 500-H1/Mach III in boxes… No problem, I had seen it run, and ALL bits was included. I restored it well, got it complete to my 18 y birthday, but had (over-)spent the budget for upgrading my licence, a car licence had priority. And sold the 500 for getting 4 wheels. If I only knew the price-increase for triples…

Anyway, had fun with Escort, Capri, Cortina/Taunus, Granada, more Capri, a Mustang, and more…but never got around to upgrade to “full” MC-licence. And never really cared about it until a few years ago. But now, it has become ridiculous priced. So, for my very limited use of 2 wheels, (just to cheat toll-roads), I can cope with the 125cc.

But, maybe it has something with weight, or, 4-stroke horsepower must be overrated. In 1980-83, my 100cc 2-stroke (un-restricted) could do 125km/h on flat ground. Any day of the week.  And, If I ever came behind a car doing less than 90km/h, I overtook it, also uphill, with passenger. Easy. Try that with a modern 4-stroke “lawnmower” engine…

Before the Hyosung found me, I had a 2014′ Honda Varadero 125, -also large & heavy, but too expensive to modify, down-traded for a 2010’ish Honda Rebel 125, with a 250 engine… utterly useless for any ride longer than 15-20 minutes (for me. Too low seat + seat-shape + would scrape footpegs before the fun started..). I also have a 79/80′ Honda CB125T (twin), undergoing a little resto-mod. (on 4 wheels: 03′ Focus 1,8TDCi Ghia & 89′ MB – 300CE /W124)

The GTR is an “overlayer” – had been standing in a shop, not beeing sold, as a 2017 model. The deal on a “new” bike was too sweet to pass, so it became mine last year, in 2021.

 

 

2016 Gt125r clutch cable replacement

Does anyone have or know where to get a replacement clutch cable for a 2016 model gt125r hyosung? I’m having trouble sourcing one for sale.

thanks

Fun and games with a GT125R

Hello everyone,

I’m hoping someone could shed some light on an issue i’ve run into while working on my son’s bike. Firstly, she won’t start anymore. No crank, just the starter relay clicking. But on the instrument panel I’ve lost the Neutral light, Full beam light and Indicator light but otherwise the guages work and the lcd display works. I’m thinking the CDI unit has died as I tested it last night and got some weird readings and then none from other. Things I’ve recently done to the bike is: Stripped and rebuilt the carbs. Replaced the Magneto/ Rectifier/ Upgraded HT coils/ Ngk laser plugs/ K&N airfilter/ New battery. We bought this bike a few months ago and it has certainly been played with over the yrs! I also checked the Kick stand switch as it has been bypassed but poorly. So reconnected and wrapped with tape. But after spending over £400 already and now my son has his CBT booked next month, I could do with some guidance before the trusty hammer of thor comes out to play!

Oil in stator cover

Hi guys, new here so excuse me if it’s obvious or has been spoken about before.

having charging issues with my Gt125r (carb)so gone to check the stator/magneto, whatever you wanna call it and dropped all my oil.

now the cover has a gasket suggesting it should hold fluid but this is a new one for me so could anyone confirm that for me please?

many thanks,

Chris

New Parts fitted from shop.. Still poor starter Gt125r

After rebuilding and thoroughly cleaning carb after purchasing 2016 gt125r found starting from cold can be a hit or a miss.

Bought and fitted upgraded 3stage yamaha regulator, Hitachi coils, NGK caps and new NGK laser Plat sparks but only resulted in a marginal improvement. BTW The whole choke assembly replaced new as bike dropped…previous owner hence low price.

I also fitted a new lead battery which I notice is only holding 12.7v…What’s your thoughts on fitting a lithium or am I wasting cash ….Wish I could retro fit a kick start.

Cant think of anything else?  Any suggestions most welcome.

Andy

 

[How to Tutorial] How to Change Oil & Oil Filter on Hyosung GV125 GV250 GT GT250R GT125R

Time for an oil change? …One of the crucial things to stay on top of!


This short tutorial shows you how to change your oil with ease on the 125/250 twins (2001-2018) and also the filter!

This applies to: GV125 (01-2018) / GV250 (upto 2018) / GT & GTR 125 (03-2018) including GT250+R.

Personally, one of my other twins gets its oil changed every 1,000-1500 miles using Ester oils. Manual suggests longer intervals, but I prefer premium oil (JASO MA2, Ester good) every 1500 miles max. 🏍️

Moving on, let’s prepare the parts & tools first…

Oil – 2x 1L Bottles
(Bike needs 1.5L total)
Oil Filter & O-Rings
(don’t skip filters!)
Drain Pan/Bucket
(3L+ capacity)
Torque Wrench
(too crucial, you’ll see why below ⏬)
Size 15/17mm Socket
(12 sided, NO SPANNER)
Size 10mm Socket / Driver

Plus these bits also: Pliers | Funnel | Gloves | Clean rags | Measuring jug

1. Undo your filler cap first!

For stock caps, use pliers (anti-clockwise). For custom CNC Caps, use 19/21mm socket.

2. Go under engine & loosen the drain plug

For GTR owners, use a bar extension or remove fairings. ⚠ Be slow to prevent the plug falling into the bucket!

3. About those drain plugs…

Roads are salty; stock plugs can seize. Use a coloured, weather-resistant magnetic plug to avoid issues. Available here.

4. Finished draining? Close the drain-hole!

Clean under the engine, use torque wrench max 15ft lbs. ⛔ DO NOT OVERTIGHTEN THIS BOLT.


5. Go to your oil filter cover next!

Undo the 3 nuts holding the cover. ⚠ Oil WILL fall out; place a rag/pan underneath. Wear gloves. Dispose old filter.


6. Filter Cover Inspection & O-Ring Change (Pt.1)

Clean the cover, check spring, replace big O-ring (dress in oil first ⛔).


7. O-Ring Change (Part2)

Replace the O-ring at the back inside the filter area. ⚠ Use a small hook, don’t force. CHANGE THE OLD O-RING TO A FRESH ONE.

8. Next, your new oil filter goes in!

Ensure the hole of the filter goes inside the engine as shown.

9. Close the filter cover!

Tighten nuts to 6 ft lbs max. 🚦 Ensure the cover O-ring is oiled.

10. Done? Grab your oil (& measuring jug!)

Pour 1.5L (1500ml). Not less, not more 😉 No jug? Use bottle markers.

11. Get your Funnel and pour the oil in…

12. Close the oil filler cap!

Ensure cap and O-ring are clean and undamaged.

🚦 Complete – Idle for 60 seconds & turn off!

Check sight glass, top-up if needed, and ensure drain plug is secure.

Tidy up & Go ride. 🏁

Questions? Fire away in the comments! 🤺

Hyosung Gt125r (2012)- Dashboard

Hi all

Wondering if anybody might be able to help. I was riding out earlier on my gt125r and the rev counter stopped working, then the lcd panel showing speed and fuel stopped working. However the neutral and indicator lights still light up.

[How to Tutorial] Adjust Carb Slide Needle (Tuning) Hyosung GV250 GV125 GT GT125R GT250R

[Tutorial] How to adjust Carb Slide Needle (Tuning) - Hyosung GV & GT 125/250
How to adjust/tune the carburettor slide needle for improved riding…


⚙ What does this do?

This modification allows the bike to reach better cruising speeds via slide needle adjustments. The throttle slide needle controls main jet fuelling as revs change. This also eliminates flat spots between 4k–7k rpm, common on 125s. For example, if the bike struggles at near full throttle, this mod helps it pull with less twist. Your bike should run better from 1st to 5th gear.

👇 Before we start, this tutorial assumes:

  • You will do this at your own risk and without rushing.
  • You have good spark plugs (e.g., Platinums) or older IX plugs.
  • Your ignition coils & HT caps are sparking well.
  • Your carb has already been upjetted (tap here…).
  • You have a performance filter (K&N, BMC, etc.), or if using a stock cotton one, cut its snorkel.

Tools needed:

  • JIS type screwdriver (+ Philips style)
  • Large & long flat head screwdriver
  • Size 7mm socket (front bolts sometimes hex shaped)
  • Watchmaker flat screwdriver
  • Clean microfibre cloth

1. Go to the right side of your bike

Spend most of your time here. Work on one pot at a time and avoid distractions.

2. Unscrew the 1st diaphragm cover

Remove the 4 bolts holding the diaphragm cover.

⚠ Disconnect throttle cable!


3. Remove the spring & diaphragm

Gently remove piston slide & spring.

4. Inspect & clean parts carefully

Use Wynns Carb Cleaner for all parts including diaphragm cover. This prevents sticking between revs/gears & scoring internal carb walls.

5. Unscrew plastic plug holding needle

Use long flat blade screwdriver, gentle ⚠.


6. Remember the order of re-fitting

Keep the image in mind when refitting small parts.

7. Remove the E-Ring (Circlip) slowly

Use a small watchmaker screwdriver. ⚠ Handle gently.


8A. Needle grooves

  • Pointy end of needle faces down
  • Push down black spacer slightly
  • Put E-Ring in 3rd groove
  • Push black spacer back against E-Ring


8B. Another view

Ensure E-Ring is in 3rd notch with black spacer pushed back. (Lowest groove, pointy end down. Factory usually 2nd or top near flat end.)

9A. Check throttle slide hole

9B. Grab needle & follow image

9C. Slot needle & mini-spring

⚠ Review step #6 and 9A/B

10. Check needle for free movement

10B. Coat throttle slide ring with oil

Prevents leaks & particle trapping.


11. Refit slide, spring & cover
  • Reconnect throttle cable
  • Ensure 4 screws are finger tight
  • Finished? Move to next cover.

12. Repeat on rear carb

13. Final check 🏁

  • Airbox clamps tight
  • Slide cover bolts finger tight (x8)
  • Throttle & choke cables checked
  • Air lines secure (prevent vacuum leaks)


Done!

Straightforward process. If unsure, comment. Otherwise, go ride! 🏁


FAQ / Troubleshooting 🎳
  • Bike runs worse after mod? Check covers & airbox for leaks.
  • No air leaks but still worse? Inspect spark plugs; ensure better sparking than stock.
  • New plugs but still worse? Check HT Cap & ignition coils. HT Cap removed ≈ 6kΩ; Coil ≤6kΩ to frame.
  • HT cap/coils high resistance? Replace both; stock ignition parts can’t be repaired.
  • Changed coils/HT caps but still worse? Ensure main & pilot jets are clean. Tap here to remove carbs.
  • Can this be done on stock 125cc? Mod will slightly enrich mid-range; jetting & better electrics improve results.

💡 Tips:

Replace the O-rings every time you remove manifolds to prevent air leaks. Always work in a clean environment as intake holes are exposed. We sell the O-rings in the shop!

For less stress, use stainless steel socket cap (Allen key head) bolts with a good CRV Allen key and tighten properly. Form A M6 stainless steel washers are recommended. In the UK, these are widely available at car shops including Halfords.

[How to Tutorial] Change Vacuum Lines on Hyosung GT125R GT250R & GT Comet (Air Hose Diagram)

Hyosung vacuum line setup

Changing the vacuum lines on carburetor 125/250 vTwins should be fairly easy. All you need is 15–30 mins of your time. Let’s start with the basics.

  • Hyosung advises that if your factory lines are 2–4 years old, discard them regardless.
  • Old pipes can rot internally, especially cheap Chinese rubber ones.
  • Larger, colder air pipes can improve the vacuum system, but use strong clips!
  • Strong clips are essential to prevent air leaks.
  • This tutorial applies to all carb-operated 125/250 GT & GTR Twins (including GV125)

Let’s go now… strip your fairings (GTR owners)

(Naked bikes can skip this step)
hyosung gt125r air vacuum line gt250 gv125

Diagram of how the “AIR LINE” system should be connected:

Study the diagram images below first before moving on.

hyosung gt125r air vacuum line gt250 gv125
hyosung gt125r air vacuum line gt250 gv125
hyosung gt125r air vacuum line gt250 gv125

VACUUM LINE #1 = CONNECT THE REAR FUEL PUMP FIRST

Got your lines ready? On the LEFT side of your bike, grab a hose for the fuel pump and follow the diagram below:

hyosung gt125r air vacuum line gt250 gv125
hyosung gt125r air vacuum line gt250 gv125
hyosung gt125r air vacuum line gt250 gv125

VACUUM LINE #2 = CONNECT YOUR FUEL TANK TAP

  • Once the rear fuel pump is connected from the left side, move to the RIGHT side of your bike.
  • Grab a second vacuum pipe and follow the diagrams below:

hyosung gt125r air vacuum line gt250 gv125
hyosung gt125r air vacuum line gt250 gv125
hyosung gt125r air vacuum line gt250 gv125

That’s it – Vacuum setup is done! 🚦

If you have an AIS device (Fake emissions/EGR), see below:


  • Refer to the cartoon diagram of the “EGR DELETE” mod.
  • Remove or block anything feeding it.
  • Example image below shows setup. Personally, it’s a useless device.
  • If you want it connected, replace “blocked” with “connected”.

EGR delete vacuum line


Alright, we are done. Go test ride! 🏁

test ride hyosung


I hope this quick tutorial was easy to follow. If you get stuck or need help, just comment on this post! This also applies to GV owners since they use the same rear pump.

Gt125r NO POWER between 4k-8k revs

Hi guys, im new to owning a Hyosung and have got a 2016 gt125r that has a lack of power between 4,000 and 8,000 revs. Anybody got any ideas or tips on how to solve this, bike only has 340 miles on the clock and its a bit annoying with having a lack of power. Thanks guys. ☺

GT125R 2007 "rear coli, no spark"

My brother have bought a GT125R 2007 rep object very cheep.

Because the previous owner couldn’t get it to start..

I found that the rear coil wasn’t giving spark, so I changed both coils for the upgraded coils.

But I now think it’s the cdi..

do enyone know how to test the cdi?

attaching some photos.

[How to Tutorial] Upgrade Fuel Lines & Filter on Hyosung GT GT125R GT250R (Carb Hose Diagram)

Hyosung Gt125r fuel lines diagram filter hose


New Fuel Lines? Let’s cut to the chase… (No pun intended!)

This guide shows how to replace your stock lines with larger uprated braided ones.

Note: If your stock/original fuel lines are 2–4 years old, you must change them, as per the service manual.


A. *️⃣ Pros & Cons of braided/fresh lines vs old stock lines

  • Larger fuel filters (3× size) benefit from gravity assist & a cleaner reserve. These filters last roughly 15–20k miles (except cheap Chinese copies).
  • Braided hoses last longer & are more heat-resistant than standard lines (40–100°C).
  • Bigger lines allow fuel to reach the carbs faster, improving response.
  • More fuel slightly improves throttle response. (Hint: Aftermarket exhausts may give a slightly deeper note.)
  • If you have upgraded carb jets, larger lines help.
  • Cons: None.

Be warned: Cheap Chinese fuel lines may fail within 1–2 years and risk leaks on a hot engine!


B. 🏍 Compatible Bikes

  • All carbureted GT125R & GT250R models (Carbs = large silver components between the v-twin engines)
  • Naked GT Comet bikes (Unsure? Comment on this topic!)

C. 🔧 Tools Required

  • Cutting tool & flat (-) screwdriver
  • 10mm / 12mm spanner or socket
  • Stubby / short (+) screwdriver
  • Clean cloth or towel

🚧 DISCLAIMER: Work in a well-ventilated area or outdoors. Fuel vapors are flammable!
Follow this guide at your own competence. Custom parts may void warranty on new bikes! 🚧


1. Remove the fuel tank

  • Use a 10/12mm spanner or socket to remove the bolt securing the tank to the frame.
  • Disconnect the 2 pipes under the tank.
  • Move the tank aside. ⚠️ Watch the Fuel Level Sensor wire! Unplug carefully! ⚠️

Fuel Lines Gt125R Hyosung
fuel lines diagram gt125 250 hyosung

2. Remove the Airbox

  • Unscrew the bolts shown in the images below.
  • 🔩 2× bolts: airbox-to-carb metal clamps (black)
  • 🔩 2× bolts: airbox-to-frame

[Tutorial] Hyosung GT & GT 125/250 - How to swap carburetor Jets
[Tutorial] Hyosung GT & GT 125/250 - How to swap carburetor Jets

3. Bike should now look like this

fuel lines gt250r hyosung diagram

4. Change the “CARB → PUMP” fuel line

  • Remove the hose connecting carb to fuel pump (rear).
  • Replace with new braided line.

– Keep lines straight! – – Tighten clamps to prevent leaks! –
fuel lines replacement hyosung

5. Finished example: Carb to Pump

fuel lines diagram gv125

6. Ditch old filter & lines! 🚮
🚧 NOTE: Fuel may spill from old filter. ⚠️ Cover your electrics!

fuel lines gt125rc hyosung

7. Grab your new filter & cut 2 short pipes

  • Use strong clamps to prevent leaks
  • Use diagram to orient the filter correctly

fuel lines carb fuel diagram hyosung
Fuel diagram fuel lines hyosung

8. Install filter to rear pump
Keep fuel lines short & kink-free!

fuel lines hyosung gv250

9. Refit Airbox

  • Return to step #2 to refit airbox
  • Tighten all bolts to prevent air leaks!

fuel lines diagram gt125 250 hyosung

10. Fit the tank

  • Connect final 2 pipes (fuel & air-vacuum)
  • Connect Electrical Fuel Level Sensor (white plug)
  • Secure tank to frame
  • Tidy up & grab your helmet!

fuel lines diagram gt125 250 hyosung
fuel lines diagram gt125 250 hyosung

Go ride! 🏁


Sidenotes / Q&A 🎳

1. Filter has low fuel? Check filter direction.
2. Filter looks good but still low fuel? Top-up tank.
3. High idle revs? Air leak near airbox or carburetors. Tighten all bolts & clamps.
4. Airbox is fine, still high revs? Check choke lever next to clutch lever. Slide toward front tyre to turn off.
5. Bike won’t start after fuel line change? Check pipes are connected correctly & filter is in right direction. Fuel should drip into filter on first crank.


The end! 🎲
If you have any questions or get stuck, reply to this topic. Hope this guide helps!

Credits 📜: Images (@Danny.M) // YouTube Video (@Luke.B)

[How to Tutorial] How to Swap Upgrade Carb Main Jets Hyosung GT GT125R GV250 GV125 GT250R

Hyosung Carb 250 125 GT GV Pilot Jets Main Jet

How to Swap Carb Main Jets on Hyosung 125/250cc V-Twins


Carb Main Jets are one of the most common upgrades on these 125/250 carby twins. This tutorial will show you how to swap carb main jets the easy way. #SwapNGo!

Important: If your bike is under warranty, check with your dealer before doing this. Doing this may void warranty on new bikes.

Anyway, let’s cut to the chase!


0. Tools Required:
  • Large Mole Grips (& small one too)
  • Philips (+) Star screwdriver – Regular Length
  • Philips (+) Star screwdriver – Stubby Length
  • Small amount of cooking oil
  • Hex Bits (& screwdriver Bit) (if you have stainless bolts on the carbs)
  • 10 or 12mm Spanner or Socket Tool
  • Flat-Head (-) screwdriver
1. Remove Side Panels & Fairings

Unscrew the bolts holding the side-panels, then take off your fairings.

Owners of Naked Bikes: Skip to #2.

Tip for GTR Owners: Place a rug under the bike. When fairings drop as one piece (left/right side panels + middle engine fairing), carefully push one side under the bike to remove safely.

2. Remove the Fuel Tank
  • Unscrew #10 (fuel tank bolt) and lift tank slightly to see fuel pipes
  • Disconnect the fuel pipe safely (marked in red circle in pictures)
  • Disconnect the small vacuum-air hose attached to the tap
  • Remove the tank from the frame. Watch out for small rubber parts that may fall out

Hyosung Tank Removal

3. Loosen Airbox Clamps

On the left side under the airbox, use a stubby screwdriver to unscrew the 2 clamps on each carb.

Loosen Airbox Clamps

4. Remove Airbox

Take airbox off and put aside. Remember the 2 bolts holding it to the frame!

Remove Airbox

5. Exposed Bike View

Bike Exposed View

6. Loosen Rubber Intake Clamps

Unscrew the clamps holding the carburetors down.

Loosen Intake Clamps

7. Lift Carbs Slightly

Leave cables & pipes connected. Fuel will be drained next.

Lift Carbs Slightly

8. Drain Fuel Safely
Do this in a ventilated area or outdoors! Fuel vapors are flammable.
  • Unscrew 2 bolts halfway (marked in red)
  • Catch dripping fuel in a bowl

Drain Fuel

9. Remove Idle Screw Adjuster

Unscrew the steel bolt holding the idle screw (left side of engine).

Idle Screw Adjuster

10. Remove Float Bowls

Remove 8 screws holding float bowls. Some may be tight; use force carefully.

Remove Float Bowls

11. Use Mole Grips if Needed

Bite bolt heads carefully if screws are stuck, then remove completely.

Use Mole Grips

12. Swap Main Jets

Install upgraded jets: one size up front & rear, depending on model.

Swap Main Jets

Stock Carb Jet Info:

  • GT125 / GT125R & RC = 87.5 Front, 90 Rear
  • GT250 / GT250R = 92.5 Front, 95 Rear
  • GV125 Aquila = 87.5 Front & Rear
  • GV250 Aquila = 90 Front, 87.5 Rear

Pilot jets remain stock: 125cc = 15, 250cc = 20

13. Install Upgraded Jets

GT125/125R = 90 Front, 92.5 Rear
GT250/250R = 95 Front, 97.5 Rear
Aquila 125/250 = One size up each

Install Upgraded Jets

14. Double-Check Jets

Ensure brass jets are snug but not over-tightened. Clean tiny holes with carb cleaner.

Double-Check Jets

15. Oil the Gaskets

Use small amount of cooking or motor oil on your fingers to coat gaskets.

Oil Gaskets

16. Reassemble Bike

Reverse steps #12 → #1. Double-check all screws & clamps.

17. Final Outcome

Final Result
Final Result 2

18. Reinstall Fuel Tank & Pipes

Check all clamps, throttle, choke line, fuel drain cable, and idle screw.

Reinstall Fuel Tank

19. Start Bike

If it doesn’t start immediately, use choke, twist throttle a few times, crank 5-7 seconds. Use Bradex Easy Start if necessary.

20. Troubleshooting
  • Fuel may take a few seconds to reach carbs
  • Use choke lever fully if needed
  • Crank while twisting throttle 5-7 seconds
  • Let idle for few mins to burn off excess fuel
21. Done! 🏁

You should be ready to ride. If you have questions or feedback, reply below!

[Download] GT GTR 125 250 R Comet Carby & EFi Service Manual & Hyosung Owners Books

[Download] GT GTR 125 250 R Comet Service Manual & Hyosung Owners Books

Hyosung GT 125 / 250 Series – Hyosung’s Most Popular Bike Range!

This topic is a living resource with links added and updated over time. Owners of all GT / GTR 125/250 models can follow it anytime for reference.

If you need specific help with these machines, post a New Topic in the “Technical Help” section.

Ok, here we go…


CARBY BIKES (Carburetted) – 1998 to 2009/2010

OTHER MODELS (HYBRID BIKES) – HALF-NEW SHAPE & RC NAKEDS

EFI / EFi / Fi BIKES (Electronic Injectors) – 2008+

(Hint: Exhaust pipe has a sensor)

@EVOCREST UK – UK GENUINE PARTS & CUSTOM ORDERS


Members of this forum can send write below requests for parts.


In this format:
Bike Details (Age, Year, CC,)
Issues / Part Needed?

You will get a price for your parts,  PLEASE SEND ME A “PRIVATE” Message with your “Address” details, so I can calculate shipping costs for you also.


My eBay Shop  (for used parts):
https://www.ebay.co.uk/usr/evocrest

PS: As the HyoRiders.club website continues to evolve, rest assured, ordering parts for your motorcycles will be improving.  Any suggestions let me know!  Stay tuned on this forum 😉