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 topic intends to show you how to swap your stock lines to larger uprated braided ones.
(By the way if your STOCK/ORIGINAL fuel lines are 2-4yrs old , you must change them regardless – As per service manual)

A. *️⃣  Pros / Cons of the braided / fresh ones vs old stock lines ?

• Larger fuel filters (3x size) benefit from a gravity assist (& a cleaner reserve). Such filters of this size last about 15-20K miles (except china)
• Braided hoses last more years & are more heat resistant than the basic skinny lines. (40-100*c)
• Carbs are less likely to wait for fuel delivery as bigger lines flow more fluid faster.
• As the bike gets more fuel = It is slightly more spirited through the gears.
  (Hint = Aftermarket exhausts will have a *very slightly* deeper exhaust note)
• If you have bigger jets installed on the bike, bigger lines help.
• Cons: None.

Be warned. Chinese fuel lines are very cheap, but why pay twice (don’t last even 1-2yrs) or risk fuel leaks on a hot engine!?

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B. 🏍 What bikes does this work on?

• All carb models of GT125R & Carby GT250Rs
  (Carburetors = That huge silver device between the two v-twin engines)
• Naked GT Comet Bikes
  (If unsure, just comment on this topic!)

C. 🔧 Tools required:

• A Cutting tool … & … a flat ( – ) screwdriver.
• Size 10mm / 12mm spanner or socket.
• “Stubby /Shortie” ( + ) Plus screwdriver
• A clean cloth or a towel rag.

🚧 DISCLAIMER: THIS SHOULD BE DONE IN A WELL VENTILATED AREA OR OUTDOOR (FUEL VAPOR!)
FOLLOW THIS GUIDE AT YOUR OWN GOOD COMPETENCE & UNDERSTAND THAT CUSTOM PARTS “MAY” VOID YOUR WARRANTY ON NEW BIKES! 🚧

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1. Let’s begin! – Remove your fuel tank.

• Grab a size 10/12mm spanner or socket & unscrew the bolt that is holding the tank to the frame.
• Afterwards, disconnect the 2 pipes under your Tank.
• Then, put the tank away elsewhere for now.
  ⚠️ Watch out for the “Fuel Level Sensor” wire too! –> BE SLOW & UNPLUG IT! ⚠️

 

2. The Air Box comes off next!

• Unscrew the bolts which are marked in the pictures below…
• 🔩 2x bolts = airbox-to-carb metal clamps (black color)
• 🔩 2x bolts = airbox-to-frame (Click for larger size images)

 

3. Your bike should be exposed like this now

 

4. Change the “CARB -> TO -> PUMP ” fuel line

• A. Remove the hose that connects the carburetor to the fuel pump (at rear)
• B. Replace it with a NEW LINE (Swap Old Line for New Line)

– – Remember, keep the fuel lines nice & straight! – –
– – ANOTHER SHOUT = TIGHTEN CLAMPS TO PREVENT FUEL LEAKS! —

 

5. A Finished Example = Carb to Pump

 

 

6. Ditch your old filter & old lines in the bin!🚮
🚧 NOTE = FUEL MAY SPILL OUT FROM THE OLD FILTER…
{⚠️COVER YOUR ELECTRICS!}

 

7. Grab your new filter & cut 2 new *short* pipes!

• Make sure you use strong clamps to prevent leaks
• Use the cartoon image to help you orient the filter the right way

 

8. Ready? Install the filter to the rear pump!
(Keep the fuel lines nice & short! = No kinks!)

 

9.  Refit your AirBox back on the bike.

• So go back up ^  to step #2 above  and fit your airbox back on the bike!
• Take your time & tighten all airbox bolts to prevent AIR LEAKS !

 

10.   Last step! Time to fit the tank now.

• Use the images below as a guide to connect the final 2 pipes. (Fuel & Air-Vacuum lines)
• Don’t forget to also connect your “Electrical Fuel Level Sensor”  (white plug)
• Once the pipes & wires are connected,  secure the tank to the bike.
• Tidy up & grab a helmet!

 

 

Go ride the bike! 🏁

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Sidenotes / Q&A 🎳 :

1. My filter has low fuel levels in it. Why?
Check that your filter is installed the right direction.

2. The filter looks good , but it is still low in fuel. Do I Top-up?
Top up your tank.  Low fuel levels make trips harder.

3.  I am getting HIGH Revs on idle, what happened ?
There is an air leak near the airbox or carburetors, so make sure all bolts are tight.
(That also includes metal clamps under the airbox too!)

4.  The Airbox is fine, but the revs are still high!
Check your choke lever  (it is next to your clutch lever) .  To turn off the CHOKE , slide it towards the front tyre.

5. The bike won’t start after changing the fuel lines….?
Check that you connected the pipes the right way & filter is the right direction.
It takes about 2 extra seconds to crank the bike after changing lines.
Here is a hint: when the bike cranks over (starting up),  you will see fuel drip in to the filter!

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

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

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

[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 😉

 

 

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

[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)

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

[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)

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

[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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