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GT250 EFI DSpec Stalls at Idle after Warm Up

I own the above mentioned bike bought second hand from the original owner who had purchased it in 2013. When I bought it, it was still under warranty with about 3000km on the clock. It is important to note that this version, the DSpec, has some minor differences in the number of sensors than similar GT250’s of that period. It is a twin cylinder equipped with Delphi electronics. The bike, which is always garaged, worked flawlessly for the first couple of years but after that it had started to loose power erratically after warm up. This was happening after about 15mins of starting from cold. From time to time I was also getting error code 132 intermittently which indicated problems on cylinder one. When the O2 sensor was inspected it was found to be covered in soot. Because of this I had assumed that the problem was limited to around cylinder 1. I replaced the plugs and high voltage cables and also swapped the coils and the O2 sensors around but the problem did not seem to change or move. I also had the injectors cleaned up by an experienced bike mechanic. I was also lucky to find a nearly new ECU which I could purchase at half price, but even this did not improve the situation.

Finally I decided to replace the coils which solved the problem completely.

Unfortunately a few more years down the line I am starting to experience a similar, though not so drastic situation so far with the bike starting perfectly but after warm up it starts missing occasionally at idle and if I stay at idle long enough the engine stalls. I don’t feel any loss in power when I am revved up.

Because of this I am starting to suspect the coils again even though these are no more than 3 years old.

Any ideas?

Regards

Another new GT250 owner

I have been oddly interested in the GT250 Naked for a few years and the right one at the right price finally came my way. I bought this yesterday, and it is as close to new as you can get. 231 miles on the odometer. 👍👍 I put 115 miles on yesterday. These are very interesting bikes. That v-twin has a WIDE “power” spread. 6th gear out on the highway, roll into a town at 30mph, and you don’t have to downshift if you choose. I’m in the USA and I suspect the  fueling is very lean( for emission standards)  in the 7500rpm range as it does not like to accelerate from that rpm. It will rev through no problems otherwise. It was very clean when I picked it up, but had to ride in some rain slop for half the ride.

[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! 🤺

Ex-Hyorider, possible future purchase..

Greetings from Michigan. I sold my ’04 GT250 a few years ago. I loved that bike, it never gave me a bit of trouble in the 2 years I had it. I may have a chance soon to pick up another 2004 GT250 for cheap. The owner says it runs good but blows oil out the tail pipe. For $250, I guess I’ll take a chance…🤞

[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.

[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] Hyosung GT125 & GT250 (Comet/R/RC) – Service Manuals & Owner’s Books

Hyosung GT125 & GT250 Series Resources

The Hyosung GT series is the most popular range in the lineup, spanning the naked GT125/250 Comet, the faired GT125R/250R, and the modern RC/P facelifts. As these bikes are very common across the UK and EU, we have preserved these official workshop manuals and owners books to ensure access for the community.

Model Identification & Technical Data

Whether you are tuning carburettors on a Gen 1 silver-engine model or diagnosing a Delphi EFI system on a newer black-engine 250cc, identifying your generation is key:

  • GT125/250 (1998–2008): Silver engine, Mikuni Carbs, “Old Shape” (Gen 1).
  • GT125/250 RC & P (2009+): Black engine, Facelifted bodywork, Carburetted or EFI.
  • EFI Models (2008+): Features an O2 sensor in the exhaust downpipe and 28hp DOHC V-Twin engines.
  • Maintenance: All models feature the iconic 75° V-Twin DOHC 8-valve architecture.

For more details, see our Pre-2009 (Gen 1) Wiki or the Post-2009 Facelift Gallery.

Carburetted (Carby) Models


⬇ OWNER’S MANUAL – GT125/250 [Gen 1]


⬇ MANUAL – GT125/250 [Facelift & Hybrid]

Electronic Fuel Injection (EFI)


⬇ EFI SERVICE MANUAL – GT250 & GV250

Need Help? If you have technical questions, please visit the Technical Help Forum.

[How to Tutorial] [Bike Mod] 650/250/125 – AiS Block Off Removal (EGR Delete)

Hyosung AIS Removal Guide: EGR Delete for GT650, GT250 & GV125

⚠ WARNING: This technical guide involves modifying the Air Injection System (AIS). Proceed at your own risk. Incorrect installation can affect engine longevity or emissions compliance. Ensure you have the correct tools before starting.

If you are looking to improve the exhaust note and throttle response of your Hyosung GT650R, GT250, or GV125 Aquila, performing an AIS (Air Injection System) block-off—often referred to by riders as an EGR Delete—is one of the most effective “free” mods available. This process is common among race teams and enthusiasts looking to strip away parasitic emissions equipment.

What is the AIS (Air Injection System)?

The AIS is designed to help motorcycles meet strict Euro emissions standards by injecting fresh air into the exhaust port. This helps burn off unburnt fuel in the header pipes. While great for the environment on paper, it often causes excessive “popping” on deceleration and adds unnecessary clutter to the engine bay. It essentially “fakes” cleaner emissions by diluting exhaust gases, acting like a parasite that steals potential engine efficiency.

Benefits of the AIS Block-Off Mod

  • Reduced Exhaust Popping: Eliminates the loud, annoying backfiring often heard with aftermarket stainless steel exhausts.
  • Improved Induction Roar: Gives the bike a deeper, more natural groan at idle and under load.
  • Smoother Mid-Range: Many riders report a noticeable improvement in the 4,000–7,000 RPM range, particularly on smaller 125cc and 250cc models.
  • Simplified Maintenance: Clears up space around the cylinder heads, making spark plug changes and valve clearances easier.

Whether you are running a stock setup or a full custom exhaust system, removing the AIS is the first step toward a true performance tune. Full credit goes to the original community author who compiled this technical manual.

Ready to start the mod? Download the step-by-step technical book below:

Community Note: This mod is highly recommended if you have recently upgraded to a Delkevic or similar aftermarket silencer.

[How to Tutorial] Clutch Plates Upgrade Replacement for Hyosung GT GV125 GT250R GT125R GV250

Learn how to change Hyosung GV/GT 125 & 250 Clutch Plates on the GV125 / 250 Engines (GT/GV)

💥 NOTE! – SOAK YOUR CLUTCH PLATES IN OIL FOR 24HRS BEFORE DOING THIS! 💥

🛠 Tools Needed

Size 8-10 “O-Spanner” Stubby Flat Screwdriver Allen Keys (if needed)
Oil Drain Pan Size 15/17/19 Sockets Pliers or MoleGrips
Rags Time Patience

Optional 19mm socket/spanner for CNC Magnetic Oil Filler Cap

🎁 Parts Replaced

Clutch Plates (fibre) Clutch Bearing Steel Clutch Discs
Oil (1.5L) JASO MA2 Grade Oil Filter & O-Rings

💪 Skill Level = Anyone can do it, but if unsure, speak to a mechanic. (Follow this guide at your own risk)

HYOSUNG GV 125 250 CLUTCH PLATES uk hysoung FORUM OWNERS CLUB

⚠ Symptoms / Troubleshooting Hints

Always replace your clutch plates when you notice the following:

  • Every 5000-6000 miles. Regardless (just like brake pads have a wear limit!)
  • When you find yourself adjusting the clutch cable frequently.
  • When gears feel notchy or hard to shift.
  • When the bike slips during gear changes.
  • Does your clutch basket “knock” during idle?
  • Does the bike “rumble” when holding the clutch lever in?
  • Acceleration is slower than before.
  • Clutch seems to “slip” on hard acceleration.

🔧 Let’s fix it….

Technical Inspection (What to look for inside)

HYOSUNG GV 125 250 CLUTCH PLATES uk hysoung FORUM OWNERS CLUB

  • Clutch Plate Thickness Limit = 2.6mm (New ones range from 3-4mm)
  • Clutch Spring Free Length Limit = 36.2mm (Normal range 3.8 to 4.6mm)
  • Deep grooves on the clutch basket? Time to replace entirely, or file gently if minimal wear.
  • Silver clutch metal discs (separators) – 1mm distortion limit.
  • Loud rattling sounds? Your clutch plates may be cracked and must be replaced immediately to avoid blocking oil passages.
  • Clutch basket center nut must remain tight with its washer intact.

🚦 Let’s begin!!!

HYOSUNG GV 125 250 CLUTCH PLATES uk hysoung FORUM OWNERS CLUB

Park your bike, get your tools out, and start with the drain pan to drain oil first…

HYOSUNG GV 125 250 CLUTCH PLATES uk hysoung FORUM OWNERS CLUB

  1. Use either 15mm, 17mm, or 19mm socket to drain the oil:
    • A. Clean the oil drain plug.
    • B. Drain all the oil completely.
    • C. Refit the plug.
    • D. Tighten to a maximum of 15 ft.lbs (20 N.M) – torque wrench recommended. If unavailable, tighten until it feels snug.
🔥 BE WARNED! – THIS IS THE “DRAIN” PLUG (DO NOT UNDO ANYTHING ELSE UNDER THE BIKE)

Drain plug warning

Ready? Get the new clutch plates and discs out…

New clutch plates ready

Remove the engine cover bolts in the blue circles. Remember where each bolt goes! Some bolts vary in size. 🔥 Be warned: leftover oil will spill out!

Oil filter warning

When you reach the oil filter rod, carefully remove it:

  1. Put two nuts on top of each other.
  2. Undo the second nut (the top one acts as a stopper).
  3. Continue unscrewing until the rod comes out entirely.

⚠ Note: Mole grips can be used with caution but may scratch the rod.

O-Rings warning

Don’t lose the O-Rings! There are 2: one for the cap, one inside the oil filter hole. Always replace O-rings & filter during oil or clutch work.

Clutch cover removal

Use a stubby screwdriver to gently loosen the clutch cover, working from the bottom and then top near the oil cooler pipes. Carefully remove the cover.

Gasket warning

🔥 NOTE: The gasket must be replaced with a new one. Old gaskets may tear.

Remove clutch bolts

Remove clutch bolts from top down gradually (25% each), then fully remove. This protects the clutch springs.

Inspect clutch hub

  • Remove the front clutch hub facia plate and inspect underlying parts.

Diagram

Inspect parts #10, #16, #17, #13 on the diagram.

Remove plates

Remove clutch plates one by one, remembering the order: First and last plates are always fibre. Steel discs go in between.

Plate order diagram

Fit back parts in this order: #13 → 17 → 16 → 9 → 10

Tightening sequence

Re-tighten clutch bolts: Start top 25%, then bottom left & right 25%, then remaining bolts to full torque. Max torque for clutch bolts = 5 ft.lbs (finger tight!).

Final steps

  • Max torque for clutch engine cover bolts: 5.5 ft.lbs (aluminium)
  • Use fresh oil, O-rings, filter, and gasket
  • Record this event in a log or back of owner’s manual to track mileage and service history

👍 Recommendation: Use high-quality 10W40 or 10W50 JASO MA2 ester oil. Avoid low-quality brands; Motul & Silkolene are best.

🏍 Ride Safe! Any questions? Leave a comment below!

[Tutorial] How to Fit R&G Crash Bars on Hyosung GT125 GT250 & GT125R

Fitting Guide: R&G Racing Crash Protectors

Protecting your Hyosung GT125 or GT250 is a smart investment, especially for new riders or those using their bikes for daily commuting. R&G Racing is the industry standard for frame sliders and crash bars, designed to pull the impact away from your expensive fairings and engine casings during a low-side or stationary drop.

Installation Overview & Protection Benefits

The GT125R and GT250R (GTR) models require specific attention during installation due to the full-fairing coverage. Properly fitted crash bars provide a sacrificial point of contact, significantly reducing the risk of cracked plastics or punctured engine covers.

  • Compatibility: Fits all GT125/250 Naked (Comet) and GTR (Faired) models.
  • Key Hardware: High-tensile steel bolts and de-embrittled bobbins.
  • Installation Tip: Always install one side at a time to ensure the engine remains supported within the frame.
  • Torque Settings: Refer to the PDF guide for specific R&G recommended torque values to avoid stripping frame threads.

Note: For GTR owners, this guide explains if any minor fairing modifications are required for the “no-cut” or “cut” versions of the R&G kits.


⬇ DOWNLOAD R&G FITTING GUIDE (.PDF)

Notice: This printable guide is a permanent mirror hosted by HyoRiders. Before starting your install, ensure you have a torque wrench and the correct socket sizes. If you have questions about fitting crash bars to the newer RC/P models, please post in the technical forums.