How to change Vacuum Lines on Hyosung GT125R GT250R & GT Comet (Air Hose Diagram)
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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)
Diagram of how the “AIR LINE” system should be connected:
Study the diagram images below first before moving on.
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:
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:
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”.
Alright, we are done. Go test ride! 🏁
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.
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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.
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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 😉
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so it just simple as getting a bolt to push into the tube and clamp it
You got it! That’s it.
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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. 🙁
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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.
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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?
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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.
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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
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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.
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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?
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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
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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?
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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
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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.
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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.
I have an 08 GT125R with only one hole in both the front, and only one in the rear intake manifold. Would this work for me too?
Cheers!
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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.
I have an 08 GT125R with only one hole in both the front, and only one in the rear intake manifold. Would this work for me too? Cheers!
Hey, I don’t see why not 🙂
For optimum performance of the vac system why not do it like this …..
Front Intake ==> T Junction (Plastic or metal) <=== Rear Intake.
The see the 3rd hole of the T Junction? Do this …..
TJunction ==> long hose to rear of bike ===> SECOND JUNCTION
SECOND JUNCTION ==> Feeds Pump and Vacuum Tap.
In other words, you just get yourself 2 junction parts so that front & rear intake both feed the vacuum of the pump and the tap. Since the pump likes it when it gets vacuum from both cylinders of the 125cc
250 doesn’t matter too much since 1 cylinder does enough , but 1 cylinder can also work for 125 , just not optimally in some situation.
Let us know how you get on or if i have confused you in anyway, ask and i will clarify again… 🙂
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Hey,
You can buy EGR blanking plates at the website shop above menu.Also, you can do this ….
Intake pipe 1 = hose.
Intake pipe 2 = hose.Run both hoses to the back —— > T PIECE JUNCTION —– Junction 1 to tank & Juntion 2 to tap.
if that was too confusing, do it how the Koreans did it originally below in a simplified way…
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