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gt250r

Gt250R

  1. Heya, so my bike starts and ideas nicely and when I go to ride sometimes rides fine for a bit then it’ll start losing power and only sit around 6-7krpms and won’t go over 70 wont gain any speed then fixes itself, sometimes it’ll do this straight away. Was running sweet for about 1000ks.
  2. Iv cleaned out carby bowels and jets
  3. Checked the plugs
  4. Checked air filter and fuel filter
  5. Cables sweet
  6. Checked for leaks around the intakes what’s else should I be checking

2008 GT250R issues

Hello all.

I’m Matt from country NSW in Australia and have just purchased a 2008 gt250r as a project to keep myself occupied, When i got the bike it did not start or run ( i paid $300) . After having the bike for a week it now has been fixed to start and run but now i have struck the issue of it stalling at 5000rpm. (this is only in neutral and not tested on the road.) I have changed fuel lines, plugs, oil and filters.

If you have come across this please let me know what your fix was,

bike will not go into neutral when running

So I have got my carb working reasonably well, some variations at idle but waiting on parts. One thing that I am wondering about is the fact I cannot get it into neutral while running. If I am at lights for a while I hit the kill switch, it will go in neutral no worries, then restart.

Wondering if this is something others have found or is this a sign I need a new clutch. I do plan on replacing the clutch very soon anyway, aiming on the next oil change. I changed the oil when I first got the bike, 500 Km ago.

Just need to figure out if I should do this ASAP or I can wait another 3500 Km.

Any thoughts and suggestions much appreciated

Finding the right needle & seat float valve for GT25R

Hi and Hello, how are you doin?

Here is my story… I got all the good bits from the shop recently, some main jets of the correct size (for some reason I had 95 front and 100 rear jets), mixture screws etc but I totally forget to get the full rebuild kit witch has the Float Needle Assembly.  I need that pretty badly it seems.

The old ones were very embedded and had been mangled somewhat by previous attempt to remove them. I managed to get replacement o-rings on there and new needles (they also may be a problem). Bike started well and ran much better than before until I left it after the ride. I returned to find fuel leaking out of the front carb at a large rate, as well as the front cylinder intake full of fuel.  Not happy Jan! I should have expected that with the condition of the seat I put in there.

So anyone way, I plan on ordering the Carb Rebuild kit but it won’t get here (Australia) until after NYE. I have found a local Mikuni Distributor that has a large number or parts but I am not 100% certain what Mikuni is in the GT250R 2006. I found I another forum that said it is the Mikuni BDS26 Double but not able to confirm.

What I am hoping to find is the dimensions of the seat in the above kit and it matches the specs of this N133.200 Mikuni I can get locally. I want to double check the ones in the bike are the correct ones as well which is why I don’t just take those measurements and I have not dissembled it yet.

It looks the same but I know, when it comes to carbs and most engine parts, 1 millimetre can make a difference.

If anyone happens to know where I can find confirmation on the Mikuni in my bike, the seat dimensions or perhaps has one they can measure will be greatly appreciated. I also need to know the Feed hole size

[Tutorial] How to Change Oil & Filter on Hyosung GV + GT125/250 +R

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! 🤺

[Tutorial] How to adjust Carb Slide Needle (Tuning) – Hyosung GV & GT 125/250

[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.

GT250R 2007 – Bike not starting (\'N\' light not lit up)

Hey guys,

I have an issue with my GT250R where I insert the key, and turn it on – but the ‘N’ light does not lit up due to which I am not able to start the bike. When I put the bike in gear, and hold the clutch and try to start – it still does not start. It does nothing on both occasions.

Now, this was an issue in the past, where a mechanic had taken out the neutral sensor, and given it a quick wipe and it kinda worked. And usually, what I have seen is, when the bike is up and running regularly, this doesn’t happen. I also ruled out the possibility of a bad battery, as I found out my battery is dead, and got it replaced with a new MBTX12U 2 days ago – still the same issue persists.

I googled it out, and found out there might be 3 switches that might be causing it – kill switch, neutral switch and side stand switch. I do think it might be something like that (i am not a bike expert though). I could actually take it to the mechanic, except coz its chrismas time most of them are shut down for the holidays, and I was wanting to get this sorted so I could do some uber eats. So thinking of trying to fix it myself if its not that hard.

Is anyone able to tell me what could be done to fix this, or how to clean those neutral sensors? I searched everywhere on the internet, but couldnt find anything. I don’t even know what these switches look like, just because I have never done this before, but I will be able to follow instructors thoroughly.

Any suggestions would be helpful.

Thanks for your time.

How to upgrade Fuel Lines & Filter on Hyosung 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)

[Tutorial] How to swap Carb Main Jets – Hyosung GV & GT 125/250

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!