Forums 🚥 PIT STOP 🔧 Hyosung Technical Help How to change Vacuum Lines on Hyosung GT125R GT250R & GT Comet (Air Hose Diagram)

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    • #1895
      ♠️ MARCEL
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      @mf448kxn6
      North UK
      GTR

      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 first.

      • Hyosung says if your “standard” factory lines are 2-4yrs old.   Discard them regardless. 
      • Old pipes can also rot inside , especially those chinese ones with trashy rubber
      • Larger colder air pipes can help improve the vacuum system but get strong clips!
      • Strong clips are very essential to avoid all possible air leaks.
      • This tutorial applies to all carb operated 125/250  GT & GTR Twins  (includes GV125 too)

      Let’s go now…  Strip your fairings down  (GTR owners)   
      (if you have a naked bike,  go to next step)
      hyosung gt125r air vacuum line gt250 gv125

       

      Below is a diagram of how the “AIR LINE” system should be connected.
       Study (look at) the diagram images below first  , before moving on to the next step….
      //
      //
      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 & follow the next diagram pictures 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 your rear fuel pump  is connect from the left side.
      * Now, move on the the RIGHT SIDE of your bike
      * Grab a second vacuum pipe and follow the next diagram images below:

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

       

      That’s It – Vacuum Setup is done! 🚦
      However, if you have an AIS Device (Fake emissions/EGR) then read below!



      *Remember above ^ , there is a cartoon diagram of the infamous “EGR DELETE” mod, right ?
      *Remove it or block anything that feeds it.
      *This image is another example for you.
      * Personally, it’s a useless device. 
      * But, if you want it connected -> replace “blocked” with “connected”
      //


       

          Alright, we are done.   Go test ride! 🏁  

       


      I hope this fast toturial was easy to follow,  however if you get stuck or need help. Just comment on this post!  This tutorial should also help GV owners since they use the same rear pump anyway.

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

    • #1918
      shane
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      @ukshane
      uk
      gt125r

      Confused with the first as it says connect pipe from fuel pump to Intake boot do I connect directly to the rear intake boot or the t junction rear pump connector

       

      And 2nd pipe from tank then do I connect to the hole of the one being removed

    • #1919
      shane
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      @ukshane
      uk
      gt125r

      I’m guessing the centre pipe as a splitter before the t junction

    • #1920
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      @mf448kxn6
      North UK
      GTR

      I’m guessing the centre pipe as a splitter before the t junction

       

      Just repeating what was on the 2D diagram but in another way to explain it 👍

      INTAKE MANIFOLDS. (VACUUM ROUTING)

      =REAR HOLE 1 = Fuel Tap (small port under tank)

      =REAR HOLE 2 — JOINS WITH —- FRONT HOLE.

      (In other words = Rear #2 & Front Hole are joined with a T PIECE junction.)

      Front intake boot always has 1 hole.

      The back has 2.

      The vacuum pump wants both 1 rear and 1 front to work properly.

      Tank Tap goes up un 2nd extra free hole given by the rear.

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

    • #1922
      shane
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      @ukshane
      uk
      gt125r

      also I just found mine as a fake egr but can I leave it installed as it is or does it after be blocked

      just if it doesn’t make a difference I was thinking of just leaving pipes connected to it saves me the hassle getting stuff to block the pipe etc

    • #1923
      ♠️ MARCEL
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      @mf448kxn6
      North UK
      GTR
      1. also I just found mine as a fake egr but can I leave it installed as it is or does it after be blocked just if it doesn’t make a difference I was thinking of just leaving pipes connected to it saves me the hassle getting stuff to block the pipe etc

      These links may help.

      https://m.facebook.com/groups/345623961212?view=permalink&id=10154901704736213

      https://m.facebook.com/groups/345623961212?view=permalink&id=10154883738251213

      That device is for euro tree huggers.  Very early GT/GV bikes didnt have them.

      Put simply. Bin it = bike is a *little* more throaty and gets rid of pops.

      Very common mod on 650s.  The forum has an EGR removal toturial for 650 but principal is the same on 125s.

       

      It is as useless as the sidestand switch 😉

       

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

    • #1924
      shane
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      @ukshane
      uk
      gt125r

      so it just simple as getting a bolt to push into the tube and clamp it

    • #1925
      ♠️ MARCEL
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      @mf448kxn6
      North UK
      GTR

      so it just simple as getting a bolt to push into the tube and clamp it

      You got it!  That’s it.

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

    • #3083
      ThrashMasterFlex
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      @thrashmasterflex
      NY, USA
      2008 GT250R

       

      So I’ve had the carb off of my 2008 GT250R for about 7 months. Having trouble figuring out hose routing for reassembly. The bike fires up just fine without any hoses attached & with the carb exposed & primed. I’m not the first owner so some things appear to have been changed. The 3 valved fuel thingy is confusing and my rear intake manifold boot only has one valve, no two.

      Is there anything redundant that I can just bypass? If not, I’m still at a loss for how to hook this up.

      I’ve labeled all the existing hoses with colors & letters. The three taps at the gas tank are labeled numerically. Please help.

       

      More descriptions:

      A(red): goes from the three valved fuel thingy to the carburetor

      B(blue): No idea where this goes? It looks the same size (inner diameter) as what I’m guessing is the fuel tank breather valve (1)

      C(green): Small inner diameter tube from rear cylinder manifold boot. **No idea where this goes**

      P(pink): Air hose from air box to cylinder pump thingy.

      Y(yellow): one line from the three valve fuel pump thingy comes out of this, it’s joined at a T juncture with the vent hose from the front cylinder intake boot valve, and they lead to the back of the cylinder pump thingy.

       

       

       

      Side question: Put my fuel tank upside down for 3 minutes and a bunch of fuel leaked out of the fuel cap. There were no gaskets there when I took it apart, and the exploded view online doesn’t seem to have gaskets either. Is it supposed to leak or should I reinforce it? Ruined my brand new paint too. 🙁

    • #3086
      ♠️ MARCEL
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      @mf448kxn6
      North UK
      GTR

      P = blocked with a fat bolt or bung, that stops the fake emissions pump. also block the hole UNDER THE AIRBOX (where P was)
      B = overflow / crash drain pipe , it goes to the GROUND (the lines goes along frame till it sees the floor, AWAY FROM EXHAUST PIPES)
      C = to tank #2
      Tank #1 = Fuel overflow to the ground (like your carb as i explained) , attach a long hose there , and run it down the suspension
      A is correct = that’s called REAR PUMP | More info about is at the original post ^

      The fuel tank lock cap has its own seals and is a spring loaded mechanism, so its always sold as one piece  sadly , sounds like you had a fishy device then.

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

      • #4769
        theJakester42
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        @thejakester42
        Southern Utah
        2008 GT250

        What is the other hole on the tank? The one that Tank #1 has a hose attached to? I’m not sure that hose is supposed to be like that.

    • #3087
      ThrashMasterFlex
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      @thrashmasterflex
      NY, USA
      2008 GT250R

      Thank you so much for clarifying that. The entire thing slowly started to make sense to me as I reread your words.

       

      So if the EGR device can simply be removed, can I remove the T juncture in the Yellow line and just run it directly from the manifold boot to the rear pump?

       

       

      Also regarding the leaking fuel cap. Since it does leak when turned upside down, is this something I need to fix or is it fine as long as I keep my tank right side up and not affect performance?

    • #3088
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      @mf448kxn6
      North UK
      GTR

      So if the EGR device can simply be removed, can I remove the T juncture in the Yellow line and just run it directly from the manifold boot to the rear pump? Also regarding the leaking fuel cap. Since it does leak when turned upside down, is this something I need to fix or is it fine as long as I keep my tank right side up and not affect performance

      The rear pump will be happier when the EGR is blocked yes.

      Feed the rear pump straight from the intake manifold 👍

       

      Tank Cap.

      Fuel may evaporate and venting issues might crop up on a hot day sometimes.

      Id replace the cap as its not user repairable. Seals tend to stay attached to the cap also.

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

    • #3093
      ThrashMasterFlex
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      @thrashmasterflex
      NY, USA
      2008 GT250R

      Thank you so much! The bike runs amazing now.

       

      as for the leaky gas cap, the cap sea itself appears to be in good working order and makes a nice seal. I think this (vent?) hole may be the culprit? Is it ok the plug that up since there’s a breather hose at the bottom of the tank anyway

       

    • #3094
      ♠️ MARCEL
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      @mf448kxn6
      North UK
      GTR

      Good to hear. Ride steady

      I wouldn’t plug anything , the bottom overflow stays open also yes. Fuel in tank can hydro lock along the lines if there is vent issues on cap or tank.

      It’s the whole cap that usually gives us drama.

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

    • #4363
      tim C
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      @atikid
      WEST YORKSHIRE
      hyosung gt125

      My set up is different to this , I don’t have two connections on the rear intake boot and the tank has no vacuum connector on it ,just two stubby connectors that connect to the fuel tap on the side of frame  😕

    • #4365
      ♠️ MARCEL
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      @mf448kxn6
      North UK
      GTR

      My set up is different to this , I don’t have two connections on the rear intake boot and the tank has no vacuum connector on it ,just two stubby connectors that connect to the fuel tap on the side of frame 😕

      It’s okay, the pre-05 had manual side mounted taps than a vacuum one.
      So as usual the tank feeds the frame tap.
      Then tap => filter => to rear pump.

      The manifolds on the engine will only feed the rear pump. Both joined in a T-piece then single line towards the rear pump.

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

      • #4842
        Benjamin
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        @knightryder
        wisconsin, usa
        gt250r

        My set up is different to this , I don’t have two connections on the rear intake boot and the tank has no vacuum connector on it ,just two stubby connectors that connect to the fuel tap on the side of frame

        It’s okay, the pre-05 had manual side mounted taps than a vacuum one. So as usual the tank feeds the frame tap. Then tap => filter => to rear pump. The manifolds on the engine will only feed the rear pump. Both joined in a T-piece then single line towards the rear pump.

        what is the frame tap?

    • #4778
      ♠️ MARCEL
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      @mf448kxn6
      North UK
      GTR

      What is the other hole on the tank? The one that Tank #1 has a hose attached to? I’m not sure that hose is supposed to be like that.

      That’s the overflow to the ground

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

    • #4839
      Benjamin
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      @knightryder
      wisconsin, usa
      gt250r

      My set up is different to this , I don’t have two connections on the rear intake boot and the tank has no vacuum connector on it ,just two stubby connectors that connect to the fuel tap on the side of frame

      It’s okay, the pre-05 had manual side mounted taps than a vacuum one. So as usual the tank feeds the frame tap. Then tap => filter => to rear pump. The manifolds on the engine will only feed the rear pump. Both joined in a T-piece then single line towards the rear pump.

      I know this is old but man this is super confusing. my bike does not have 2 connectors. can someone please explain what the frame tap is?

    • #5383
      ♠️ MARCEL
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      @mf448kxn6
      North UK
      GTR

      My set up is different to this , I don’t have two connections on the rear intake boot and the tank has no vacuum connector on it ,just two stubby connectors that connect to the fuel tap on the side of frame

      It’s okay, the pre-05 had manual side mounted taps than a vacuum one. So as usual the tank feeds the frame tap. Then tap => filter => to rear pump. The manifolds on the engine will only feed the rear pump. Both joined in a T-piece then single line towards the rear pump.

      I know this is old but man this is super confusing. my bike does not have 2 connectors. can someone please explain what the frame tap is?

      Frame Tap = Tap that is mounted on the left side of the frame and it has ON/OFF/RESERVE markings on it. GTR bikes use vacuum taps since they entered the market. Later GT nakeds switched to vacuum taps on their new shape bikes

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

    • #5687
      fadlan
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      @fadlan93
      malaysia
      gt250r

      hi,

      so my bike got 1 rear intake hole, 1 front intake hole with rear pump and vacuum fuel tap.

      how can i apply this method?

      would appreciate much if could help me.

    • #5689
      ♠️ MARCEL
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      @mf448kxn6
      North UK
      GTR

      hi, so my bike got 1 rear intake hole, 1 front intake hole with rear pump and vacuum fuel tap. how can i apply this method? would appreciate much if could help me.

      Hey its OK.

      Front intake pipe = fuel pump.

      Rear intake pipe = vacuum tank tap.

      Only GT250R & GT250

      Any 125 owners should follow the original topic at the very top above ^^

      Hope that helps.

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

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