How to upgrade Fuel Lines & Filter on Hyosung GT125R GT250R (Carb Hose Diagram)

[♠️ MARCEL]

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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.

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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!

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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! 🚧

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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! ⚠️

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

3. Bike should now look like this

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! –

5. Finished example: Carb to Pump

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

7. Grab your new filter & cut 2 short pipes

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

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

9. Refit Airbox

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

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!

Go ride! 🏁

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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.

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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)

[Trevor]

Great tutorial on braided hoses and fuel filter upgrades.

[Sean]

Thats answered  some of my questions but my tank dose not have that it has 2 pips that come down to a fule tap with one connect on top and 2 on the bottom so am guessing set up will be different? Or the guy i bought the bike off was laughing all the way to the bank

[Nathan]

Good afternoon

Referring to Step 10:

My tank doesn’t look like this. It’d only got 2 nipples where the fuel hoses connects to.

Can you please clarify this for me?

PS: you refer to the fuel pump as the “rear pump or pump at the rear”.  Does this mean that there is (or should be) a fuel pump in the front aswell?

[♠️ MARCEL]

Nathan wrote:

Good afternoon Referring to Step 10:

 My tank doesn’t look like this. It’d only got 2 nipples where the fuel hoses connects to. Can you please clarify this for me? PS: you refer to the fuel pump as the “rear pump or pump at the rear”. Does this mean that there is (or should be) a fuel pump in the front aswell?

Quote

 

Hey.  If you have a tank thats only got 2 holes under it. You have a classic Comet tank which doesnt use a vacuum tap.

 

So each hole under tank (2 of them close to each other)

Goes down to the  MANUAL ON/OFF TAP that is mounted on the left side of the bike frame.  Usually older comets with Silver Frames have this.

 

Late models switched to vacuum taps (hence needing a vacuum pipe from intake manifolds to make turn on/off automatically.)  (& all GTR 125 whatever year they always are vacuum type taps)

 

REAR PUMP = It sits behind the rear engine of your bike.

As you saw in the pictures above ^. There is only 1 for all GT / GTR  from 125cc to 650cc carby bikes.  Its the same Mikuni unit Koreans use.   Carb is a Mikuni too 😉

 

 

[Nathan]

Excuse me for being stupid but if you say “manual on/off tap” is that the petcock?

[♠️ MARCEL]

Nathan wrote:

Excuse me for being stupid but if you say “manual on/off tap” is that the petcock?

Quote

Yes , it sits on the left side of the frame (mounted there)

[Reece wood]

I’m struggling to get fuel from my tank into my carb, I’ve bought a new fuel pump and I’ve checked the hoses for any blockages. when I manually suck on the vacuum pipe fuel comes out of the fuel pipe but when I connect everything back up and try to start it nothing goes into to fuel pump and then into the carb, was wondering if there was anything I could try?

[♠️ MARCEL]

Reece wood wrote:

I’m struggling to get fuel from my tank into my carb, I’ve bought a new fuel pump and I’ve checked the hoses for any blockages. when I manually suck on the vacuum pipe fuel comes out of the fuel pipe but when I connect everything back up and try to start it nothing goes into to fuel pump and then into the carb, was wondering if there was anything I could try?

Quote

Fuel tap is faulty (just replace it as it will 100% leave you stranded) or there is lack of vacuum to open the taps when engine cranks.

Lack of vacuum follows on

• Rotted / Old ORings under the rubber intake manifolds
• Airbox is not sitting in the carb 100%  (especially the front where tiny air still gets sucked in)
• Intake manifolds  (spray carb cleaner when running to see if revs change , then intake pipes have a problem)
• Loose vacuum hoses or clogged hoses (i hope not)
• metal manifold clamps holding the carbs down are loose.   (don’t overtighten as inlets are very difficult to get brand new)

[Reece wood]

♠️ MARCEL wrote:

Reece wood wrote:

I’m struggling to get fuel from my tank into my carb, I’ve bought a new fuel pump and I’ve checked the hoses for any blockages. when I manually suck on the vacuum pipe fuel comes out of the fuel pipe but when I connect everything back up and try to start it nothing goes into to fuel pump and then into the carb, was wondering if there was anything I could try?

Quote

Fuel tap is faulty (just replace it as it will 100% leave you stranded) or there is lack of vacuum to open the taps when engine cranks. Lack of vacuum follows on

• Rotted / Old ORings under the rubber intake manifolds
• Airbox is not sitting in the carb 100% (especially the front where tiny air still gets sucked in)
• Intake manifolds (spray carb cleaner when running to see if revs change , then intake pipes have a problem)
• Loose vacuum hoses or clogged hoses (i hope not)
• metal manifold clamps holding the carbs down are loose. (don’t overtighten as inlets are very difficult to get brand new)

Quote 

thank you, it’s a 2013 so it doesn’t have a fuel tap, it’s something to do with the vacuum, I’ll give those a try and if still nothing I’ll be back in touch, thanks again

[Reece wood]

I’ve tried everything you said to try and the bike still doesn’t want to start, is there anything else I could try?

[Author]

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