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

[♠️ MARCEL]

How to swap Carb Main Jets on Hyosung 125/250cc v-Twins

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Carb Main Jets one of the most common upgrades to do on these 125/250 carby twins.   This tutorial will show you how to swap carb main jets the easy way.  #SwapNGo!

First things 1st, if your bike has warranty, consult your dealer before attempting this. This may void warranty on new bikes.

Anyway, Let’s cut to the chase!

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0. The tools required:
– Large Mole Grips  (& a small one too)
– Philips (+) Star screwdriver – Regular Length
– Philips (+) Star screwdriver  – STUBBY LENGTH (Shortie)
– A 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. Whenever you’re ready, unscrew the bolts that hold the side-panels of your bike. Then take off your fairings!

Owners of Naked Bikes = Skip to #2.  (GT Comet)

Tip for GTR Owners  = Place a rug under the bike,  and when your fairings drop to the floor as “ONE piece”.  Carefully push one side under the bike, so the whole “one piece” can come out safely off the bike.   One Piece means “left/Right Side Panels & Middle Engine fairing attached as one.”

 

2.  Get the tank off the bike next…
* Unscrew #10 (fuel tank bolt) pictured below & lift up the tank “slightly up” so you can see the fuel pipes.
* Disconnect the fuel pipe safely from under your tank  (marked in red circle!)
* Don’t forget to also disconnect the “small” vacuum-air hose that is also attached to the tap
(Some GT Naked bikes use a manual tap on/off Tap instead of a vacuum fed tap)
* When the pipes are off,  remove the whole tank away from the frame. 
(Watch out for item #3 – These rubber things fall out sometimes)
(Save Picture to device to view it much larger)

3.  Loosen the airbox clamps
On the LEFT side of your bike, directly under the airbox.  Grab a stubby/shorty (+) screwdriver and unscrew loose the 2x clamps on each side of the carb.
They are marked in the red arrow as reference.  They are black in colour.

4. Remove the airbox away from the bike.
Take your airbox off & put it aside for now.  Jump to #5 next.
* Don’t forget to remove the 2 bolts holding the airbox to the frame!

5.  Your bike should now be exposed like this…

6.  Next up, let’s loosen the rubber intake clamps…
On the red arrows pointed -> unscrew loose the clamps holding the carburetors down.

 

7. Lift up your carbs out of the intake boots   (just a little!)
Yes leave everything still connected (cables & pipes)
We still have to drain the fuel out , so jump to #8

8. Get a bowl & do this on a VENTILATED area or outdoors! (Fuel Vapor)
* On the red arrows , unscrew these 2 bolts about half-way out.
* Fuel will start dripping down the small pipes under the bolts
(fuel is draining out)
* Grab a bowl or bucket and capture the fuel  (watch for spillls!)

 

9. When the fuel is drained completely…
UnHook the idle-screw adjuster.
* On the left side of your engine, there is a black “hand” screw that controls idle speed.
* Unscrew the STEEL bolt that holds it down  (Look at red circle picture)

GT Comet Owners = Skip to #10.

10. Phew…. Let’s remove the float bowls now!
You can do this SIDEWAYS  or  FLIP the carbs over a bit, as pictured below…
Remove the 8 screws that hold the float bowls down.
* Be warned! = Some original screws can be harder to unscrew loose. So be ready to use some force!
* To be honest,  Mikuni should really start using stainless bolts anyway!

 

11. Struggling?  Grab a pair of mole grips!
* When a screw is being difficult to remove with a screwdriver.
* Adjust your mole grips to bite a small bolt head
* Make sure it’s strong enough , so it’s doesn’t slip!
* Bite the bolt head –> Turn left. It should squeek loose.
* When the “bolt” is loose, use your original screwdriver to remove the bolt entirely.
* * * It’s common for these carbs sometimes to have rusty looking screws.  * * *

 

12. Finally,  we get to the real thing.  Your carb’s undersides should be exposed now!
* Next  up , get your “Upgraded” Jets ready!
* Take a 5 min break!
* You are going to swap your standard carb main jets jets for the bigger ones.

 Information On Carb Main Jets 
Depending on which model 125/250 v-twin , it is important to remember these points:
* Stock GT125 / GT125R & RC = 87.5 Front Main Jet & 90.0 Rear Main Jet
* Stock GT250 / GT250R = 92.5 Front Main Jet & 95 Rear Main Jet
* Stock GV125 Aquila = 87.5 Front Main Jet & 87.5 Rear Main Jet
* Stock GV250 Aquila = 90.0 Front Main Jet & 87.5 Rear Main Jet

All 125 vTwins = Size 15 Pilot Jets (Front & Rear) = Don’t change it.
All 250 vTwins = Size 20 Pilot Jets (Front & Rear) = Don’t change it.

• If you change exhaust pipes to “free-flowing” (aka. stainless pipes/straight through) = Then it is even more necessary to upJet the v -twin carb main jets.
  If you have an aftermarket Air Filter such as “K&N” =  You also need to upJet
  (more air = more fuel!)

 

13.  Ready? Let’s upgrade!
Swap the front & rear carb main jets for one size up each.
GT125/GT125R = Upgrade to 90 FRONT  & 92.5 REAR
GT250/GT250R = Upgrade to 95 FRONT & 97.5 REAR
or
GT250/250R = 95 & 95    ( For Aquila 125/250 = One Size Up each. )
* Okay, see the red circles ?
* Unscrew each jet  & replace them with a bigger one.

 

 

14. Double check that the jets are secure & tight before closing up!
* Take note! – These jets are brass, so don’t over-tighten them!
* Make sure your carb is also clean from any visible dirt or dust particles.
* The Jet Holes are very tiny! …(So a clean area is a must)
* A Carb Cleaner helps clean up old carb parts & carb main jets !

15.  Grab some cooking oil (or old motor oil)
* Drop a “SMALL AMOUNT” of oil on your FINGERS
* Use your fingers to SLIDE OVER the black gaskets…
* Keep doing this until both gaskets have a nice coat of oil-film over them.

 

 

16. All done?  Time to close everything up,
^ let’s do things in reverse now ^  #12 -> #1…  
Start from #12 going back to #1  –  Always double check each step you take!
Fit all your parts back together.

 

 

17. In the end , this should be the final outcome

18. Install the Fuel-Tank (& also connect pipes!)
* Also, check that all screws are nice & secured  such as:  2x Intake Rubber Clamps, 2x Airbox Clamps, Carb-Float Bowl Screws & 2x Carb-Fuel Drain screw closed up too.
* Inspect your throttle cable (Twist your throttle grip to test!)
* Ensure your Choke Line is working   (Test your choke = The carb  will slide its choke rail!)
* Check your fuel drain cable is AWAY from the engine  (zip tie to frame & let it point to ground)
* Lastly,  make sure the “ENGINE IDLE” HAND-SCREW is also attached properly 

19. You should now be ready to start!
This quick ten second video was taken, while the bike was still cold & we swapped carb jets.
This 125RC was only 600 miles old, no choke was used.

 

 

20. Trouble starting? 
* If it doesn’t start the first time around.  That means the fuel inside the carbs hasn’t reached “capacity” yet.
* Put the CHOKE lever on max setting (towards YOU)
* Then Crank the bike for about 5-7 seconds (while TWISTING the throttle a few times).
* Then it should fire in to life.   Let it idle for few mins to burn off any excess fuel that could have made the spark plugs wet.

Still got some trouble? Get a can of Bradex EASY START – Spray lots of it inside your air filter hole. Now crank the bike again & it should fire this time round!

Factory Troubleshooting Guide for starting issues.
(Save the images to your Device to view it much larger)

 

 

21. The end!🏁

You should be miles away in to the countryside or your other scenic spot!

I hope this tutorial was easy for you to follow.  As always, if you have any questions or feedback,  just reply below!

– M

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

[Teddy]

Hi, im New to motorbike mods and may seem like a noob question but where do you get the jets from because I’m seeing sellers asking to make sure there the right size as there all different, also looking on just eBay for k&n air filters it claims it makes no difference to a stock setup are they worth getting if I have ss pipes, thanks in advance

[♠️ MARCEL]

Teddy wrote:

Hi, im New to motorbike mods and may seem like a noob question but where do you get the jets from because I’m seeing sellers asking to make sure there the right size as there all different, also looking on just eBay for k&n air filters it claims it makes no difference to a stock setup are they worth getting if I have ss pipes, thanks in advance

If you can’t get Mikuni jets for your bike , just email me and I will find out for you.Do you know a local bike garage that keeps a stock of jets as the Mikuni brand is used on other bikes too. I always send out some bolts, ebc jets & filters to some who already have ss pipes.

If you get jets from another source, be wary of cheap china brass as they gum up easily!
Can be a nightmare cleaning them out haha.

K&N 650 filters push about 2/3x more air than stock.   In fact, the stock setup already needs bigger jets as the factory versions are too small.

If you have SS pipes  or K&N Filter  (whichever comes first) ,  jets will need to be changed or there is a risk of overheating the rear or piston wall glazing.

Take out your spark plug –  this colour below (coffee brown) means fuel / air / exhaust system is optimal.
Center is “CREAM / BIEGE” in real life.

If its a pure white colour in the center, then it’s lean, which doesn’t help with the risks i mentioned above ^ ^

If it’s sooty black = that means it’s rich, the fueling system needs cleaning (carbs in this case) or plugs / coils need inspecting or  it’s getting too much fuel with less air   (clogged filter)

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

[Dan]

Hi I used your guide to clean my jets as the bike I have purchased had problems with idle and sluggish power. I presumed it was due to dirty carb. I took it apart found lot of dirt inside the float bowl and clogged jets. Cleaned it up a little bit, put everything together and bike does not start. I can see bit of leakage on the rubber intake , as seen on the pic below, but it is all correctly inserted into the rubber and the clamps are tigthened. What do I do to stop the leakage ? Is it the reason for the bike not starting?

dav

[♠️ MARCEL]

I think your “float bowl” gaskets are leaking  or the bowls aren’t screwed in tight (maybe one bolt is looser than rest)

I’ve seen this happen a few times to some ,   usually you can drain the fuel again…then expose the carb bowls.

Investigate the gaskets. If they look crushed or flat, they probably need replacing.

Or re-tighten each bolt that is on the float bowl.

A leak does prevent start ups.

Also, i’d 100% recommend changing the oil as soon as possible , as any wet fuel pouring down the piston chamber, will mix with the oil , glaze the piston walls soon.

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

[Dan]

The screws on the float bowl are bit rusty so I’ve tried not to damage them. I have ordered a new set of stainless steel screws from here and new orings for the floats from another shop. I will give it another try this weekend again and see if it helps. I will also replace the oil, even thou I just changed it before I started working on the carb 🙁 but I prefer to have a healthy engine 🙂 Thanks for the help, I will post the update once I replace all the parts.

[Daniel]

hello

Very good information over here!

I have a question.. how many turns, after all this mods, do you have at the pilot/air screws??

big thanks

 

 

 

[♠️ MARCEL]

Daniel wrote:

hello

Very good information over here!

I have a question.. how many turns, after all this mods, do you have at the pilot/air screws??

big thanks

Good question, but according to the manuals (which i agree with), is that the C/O (air fuel mix screws are usually pre-tuned at factory and must never be touch, hence they hide the gold screws with a rubber bung.

The reason for that is also the front and rear engine don’t spark at the sametime, jetting is lager on one carb , then front etc.. so “usually” with these carbs on a 125-250cc type of bike would be about 2.75 – 3.5 turns out – more or less depending on jetting on carb too.

The biggest hint = plugs will be coffee brown , that means stop there & the bike is all set.

However, most mechs don’t always know this and i can’t be surprised when ignore the service manual warnings haha.

Anyways, to put it short. The stock carbs don’t need that kind of tune. Only thing to do is uprate the jets (more fuel) = then add more air (better air filter) then its a happier bike.

“Pilot Jets” don’t need replacing as they as good as they get on the 125 twins, only “extreme” tuning would require air fuel tuning or pilot jet swapping.

Only Main Jets is what most of us all do with a K&N Filter – for a “plug n play” simple weekend!

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

[shane]

im guessing doing upjet is if you having a new exhaust upgrade or air filter performance

[♠️ MARCEL]

shane wrote:

im guessing doing upjet is if you having a new exhaust upgrade or air filter performance

Stock machine = Upjet it anyway (the rear is a little cooler as fuel has a cooling effect) & should run a little better in 5th.

Modded machine -> K&N Air Filter  or  Stainless Exhaust pipe or End CAN = upjetting mandatory ofcourse.  Modded bike ? = Baffle runs better with baffle in than without baffle on any 4T (& quieter anyway! 😉 )

Laser or IX plugs help a lot.   If the plugs are “coffee brown”  the bike is happy!

The stock ones are too sooty & a nightmare for UK winters, usually chuck em first thing lol.

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

[shane]

Hi Guys

I’m looking to upgrade my main jets and do a carb rebuild at the same time. My GV125 had been stood around for sometime before i bought it, in saying that i got lucky getting it going but i know it needs attention very soon. I’m looking for the correct jet size and a rebuild kit for the carb’s. As well as this I’m after some tutorial on how best to remove the carb’s as it was a nightmare the last time i done this and don’t want to struggle unnecessarily. Its fitted with straight through ss exhaust also,  thanks in advance Shane

[♠️ MARCEL]

shane wrote:

Hi Guys I’m looking to upgrade my main jets and do a carb rebuild at the same time. My GV125 had been stood around for sometime before i bought it, in saying that i got lucky getting it going but i know it needs attention very soon. I’m looking for the correct jet size and a rebuild kit for the carb’s. As well as this I’m after some tutorial on how best to remove the carb’s as it was a nightmare the last time i done this and don’t want to struggle unnecessarily. Its fitted with straight through ss exhaust also, thanks in advance Shane

Hey,
If your local dealer doesn’t have genuine Mikuni jets / EBC ones ,   you may send me a message as I for sure keep a stock of older genuine (on ebay) & some new jets.
I usually send jets with air filters on some custom orders.

I have dealt with the GV bikes a few times, one thing is for sure:
– Pilot Jets do not need upgrading at all.
– Stock main jets are identical  (87.5 front / 87.5 rear)

So a good upgrade commonly is the “90 Main Jet (Front)” and “92.5” (Rear)
Ofcourse the rear is bigger as its the hottest engine, so a bit extra fuel at the back has a cooling effect & slight torque boost in 5th gear.

If you head to Halfords or EuroCarParts – My fav cleaner for carbs is  WYNNS FUEL SYSTEM CLEANER – It’s a green can  , ofcourse any good carb cleaner will blast every hole clean.

Also , i must stress a little here – The “STARTER JET”  (which can’t be removed) has a very very tiny hole , ensure you have a good carb cleaner.

After the STARTER JET  (that big metal tube that you can’t remove) is cleaned up, your bike will start a LOT faster.

Starting / Cranking  = Starter JET
Slow Ride / Idle  = Pilot Jet/Main Jet
Normal / fast Riding = Main jet.

1 more thing.   Head over to poundland & get 3 cans of AIR DUSTER –  When the jets are dry , use the air duster to blow the holes clean.

Use the air duster to blow everything inside the carb, after it has dried up from a carb cleaner liquid.

A full clean will really do wonders to the bike. Good luck!

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

[shane]

Quick up date. I have stripped and rebuild my carbs, as I suspected there was a build up of crystallised fuel due to the bike standing for a long time. I replaced the stock main jets with 90 front 92.5 rear. Started the bike first time and much better then before, I let it worm up to clear sny cleaning solutions that may still be in the carb. Took the bike for a test ride but it feels like it’s not fueling correctly. As it splutters them revs back up as it should. I had to replace the fuel line as original lines where perishing, but the fuel line is a little to sma I think. Any ideas to what’s wrong. Everything was free and moving as it should on the carb before putting back on to the bike.

Cheers shane

[♠️ MARCEL]

shane wrote:

Took the bike for a test ride but it feels like it’s not fueling correctly. As it splutters them revs back up as it should. I had to replace the fuel line as original lines where perishing, but the fuel line is a little to sma I think. Any ideas to what’s wrong. Everything was free and moving as it should on the carb before putting back on to the bike.
Cheers shane

– Pilots = affect idle and slow moving , so pilot jets should be clean
– Spark Plug – Clean it , with that carb cleaner – it should spark better, if not IX or Lasers will wake it up better (& bog less under some load) – Stock plugs are just that woeful.
– Fuel lines – Ofcourse, adding thicker high temp lines only add to “more fuel in the pipes = bigger hole” & “fuel is colder = less misting on hot temps, comes to carb as liquid than a misty hot gas)
– Main Jets hopefully should be cleaned up too.
– The “BLACK CV SLIDERS” are critical , they are the mother of the carbs , so you want to make sure they “retract” up & down fast without any delays – that means there is no particles stopping the Sliders moving when you add revs to the bike

When you rev , they slide up – they must not delay whatsoever.

Hope this info helps!

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

[shane]

I will change the fuel lines as that’s all I can think is coursing the problem, I have lx spark plugs fitted already. I like the style of the bike but it will be in parts for ever if it carriers on annoying me!

[shane]

So had another quick look at the bike, I took the air filter off so I could access the carb. I thought I would start it up just to see what it was like and in my opinion it ran better!? I also noticed some black bungs at the bottom of the carb, so removed them to reveal screw heads. What are these for? Also choke is working better with air filter removed. Do I have a mixture problem here? Any help would be appreciated

Shane

[shane]

[♠️ MARCEL]

shane wrote:

So had another quick look at the bike, I took the air filter off so I could access the carb. I thought I would start it up just to see what it was like and in my opinion it ran better!? I also noticed some black bungs at the bottom of the carb, so removed them to reveal screw heads. What are these for? Also choke is working better with air filter removed. Do I have a mixture problem here? Any help would be appreciated

Shane

Bungs hiding gold screws = Air / Fuel Mixture = Only the factory tunes that. Dealers are told not to touch it whatsoever , otherwise re-tuning is a serious abyss here. I agree with the koreans.

If it runs better without a filter = Investigate air filter (clogged?) or spark plugs (glaze brown means they are healthy)

Glaze brown plugs also mean = carb / filter / electrics are doing well.

To increase mixture = Either add 1 step up from a factory main jet (90/92.5)

Pilots remain size 15 each but must be clean = smooth rolling idle is dependent on pilot jets

Again, investigate your black CV sliders on the carb
Idle and revving up to 7k rpm etc = they slide up
Dropping revs to idle = they slide down

Particles on the slider will grind against the carb walls = certain rpms will be bouncy, certain rpms will be jerky –> carb sliders may be hanging

Cleaning them fixes this.

If the sliders are “retracting” fast & (as quick as your throttle moves) – they should be working on

This clip will hint , why its critical the sliders work nicely … (idle , through gears , warming up)

 

The real key to a free flowing bike is to attack these at once:
Coils , Spark Plugs , Clogged Jets , slow retracting black tube sliders, good fuel pump working , air filter is new (PAPER FILTERS LAST 2-3K before they start to give you less air for carbs)
5k would be pushing it.

If its a fabric / cotton gauze filter – it generally is okay until approx 7-10k , the filter will hint how dirty it is.

———————

“UNLESS” – Someone in the past ever messed up the mixture screws (which were hidden behind black bungs) , then it can explain cause not mixing air intake & petrol properly inside. Like i said, it would be an abyss to retune it back as Koreans never revealed the adjust settings, they do that before shipping the bike away. Depends on country & market its going to.

So the home owner, may go through few spark plugs until its right (plug chopping business)

But honestly, the spark plug colors will tell you how rich or lean the bike is.

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

[shane]

Thanks for the reply. I will look at the black sliders again tomorrow night. The bike was played with before I had it so it could be anyone of the faults you have mentioned.

Cheers shane

[shane]

So checked the black sliders and they move freely, the bike will idle for a bit but runs uneven, revs up and down, then after a little but of time it just cuts out. I know this to be a common fault if the coil is breaking down. Do I start chucking money at it!?

[♠️ MARCEL]

shane wrote:

Do I start chucking money at it!?

Probably,

The bike still isn’t happy = Look at your own spark plugs , will tell you exactly if its electrical / fueling / or poor air system. (Rich vs Lean vs Poor Electric Sparking)

Bike will not ride perfect unless all 3 work in tandem (air / fuel / sparking electrics)

I would read my replies above ^ on this topic = write down as a list. tick off every single checkpoint.

Fueling Parts & Carb OK & checked over? = then we are done with the carbs.

Then the electrics or plugs would be your enemy , I would go here below …
(GV125/Gt125 = same engine, same carb, same coils = same behavior)
(Follow my replies in those threads, as i go quite deep on electric dramas & HOW to test them yourself)

1. https://hyoriders.club/forums/topic/gt125r-no-power-between-4k-8k-revs/

2. Another Topic Here

3. And this one too!

Yes,
Faulty Coils & Regulators happen to all hyosungs. They are just a cheaply made parts that die out eventually. The japanese win when it comes to electrics.
— > Could also explain your plugs not doing their job or otherwise fouled/annoyed

Remember this always:
High revs / RPM needle stuck high / very slow to drop revs down = Air Leaks (anything air flows thru) or CV sliders stuck or choke is not off (still on choke)

Boggy / Jumpy Revs / Laggy = Electrics (inspect all including plugs , can’t stress spark plugs enough) or Fueling Drama (anything that petrol flows through)

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

[Josh D]

I have a GT125R 2015 and the exhaust end can i have ordered is an sc-project crt, this exhaust end can is straight through, what would you recommend? should i get the 90 front and 92.5 rear main jets or bigger. also the exhaust can has no baffles with it.

[♠️ MARCEL]

Josh D wrote:

I have a GT125R 2015 and the exhaust end can i have ordered is an sc-project crt, this exhaust end can is straight through, what would you recommend? should i get the 90 front and 92.5 rear main jets or bigger. also the exhaust can has no baffles with it.

You will loose the intial torque that you want when taking off, the baffle should be inside , and a baffle with a hole size (inside or out)  of  a 10p size, is a good sized hole.  HUGE HOLE baffles are almost pointless but still better than without 😉

Fuller size cans do better than shorties on any 4T bike if im honest, ive found out the same on both 125 n 250 hyosungs,    No baffle = it will scream more to get going at the same speeds sometimes.

90 and 92.5 is enough for 125s.

Then follow this tutorial below  (it improves ur 90 n 92.5 in top gear, also 4-7k rpm flat spot fixing)(so extra mod)

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

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

[Robert Wilde]

Hey Everyone,

I am working on getting my 2006 GT250R on the road for the first time and this forum is a massive help.

First thanks for an awesome article, I am awaiting all my new bits to make it happen and I glade I found this article. It seems someone else, previous own, had been playing around with the carb a bit.

First thing I found was both needle acorn nuts broken and barley seated.

Then I found that it has weird jet sizes, they are labelled 95 and 100. From what I have read here, the stock is 92.5 Front Main Jet & 95 Rear Main Jet, and the upgrade is 95 and 97.5 which I have on the way to me now.
Not sure how much of difference this makes. Something to note is both air fuel mix screws were set at 3.25 turns out. Will return to same position but may need some adjustment, not sure.

One thing I need some input on is the hose in the middle between the 2 carbs, I believe it is a breather port. I circled it in the below image. Super annoying as it is in the diagram for the carb service manual but not in the carb parts list manual.

Can anyone confirm it is a breather tube?

[♠️ MARCEL]

Around 1.5 to 2.5 turns on the GT250 but caution this because KR didnt reveal it and heavily discourages messing with the mixtures. And also caution that rear engine likes to run a little richer (a little).  hence the 2.5 step staggered fashion of jetting KR did for the 125 and 250 models.

In your pic. Yes it is a breather / overflow to the ground incase bike tips over (falls) or floats act strange and overflowed the carb (in the sense of the word)

Hope that helps.

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

[Robert Wilde]

Very much, Thanks Marcel.

[Luke]

Hi everyone.

I am looking to upgrade the main jets on my GV125. Looked at Mikuni main jets on eBay. There are lots of sellers selling different shapes any types. I know I need a 90 front and 92.5 rear. But which type.

Thanks in advance.

Luke

 

 

 

[Moustache Man]

Luke wrote:

Hi everyone. I am looking to upgrade the main jets on my GV125. Looked at Mikuni main jets on eBay. There are lots of sellers selling different shapes any types. I know I need a 90 front and 92.5 rear. But which type. Thanks in advance. Luke

Quote

 

Hi Luke!

I have the answer to your question!

https://www.wemoto.com/parts/picture/hl-229092_5

Check this link out, look for the code in the title if you dont wanna buy them from WeMoto or if they arent the correct jetting. These should be the right ones, if you search up that code on the internet, you find the specific Mikuni carburettors that are listed in the Specs guide of the GV125 (i did this research myself, you can double check if you like just to be safe)

Hope this helps. Cheers

[Luke]

Thanks very much

[Luke]

Im having trouble removing the airbox from my GV125. All screws and clamps are removed or loosened. Can’t physically remove the airbox. The top frame tube is in the way and stopping me from getting it out. Is there a technique to it.

Thanks Luke

 

[♠️ MARCEL]

Luke wrote:

Im having trouble removing the airbox from my GV125. All screws and clamps are removed or loosened. Can’t physically remove the airbox. The top frame tube is in the way and stopping me from getting it out. Is there a technique to it. Thanks Luke

Quote

Have you searched or browsed the forum.  There was a discussion about this.  If you cant see it, I will try to find it when i return back.  it wont be easy but patience.

I can only say PLEASE do not stress the manifolds. They are very very hard to buy these days.

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

[Luke]

♠️ MARCEL wrote:

Luke wrote:

Im having trouble removing the airbox from my GV125. All screws and clamps are removed or loosened. Can’t physically remove the airbox. The top frame tube is in the way and stopping me from getting it out. Is there a technique to it. Thanks Luke

Quote

Have you searched or browsed the forum. There was a discussion about this. If you cant see it, I will try to find it when i return back. it wont be easy but patience. I can only say PLEASE do not stress the manifolds. They are very very hard to buy these days.

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I found the discussion on the perils of removing the air box. Best suggestion is to access the side plate on the left hand side of the carb with everything still in situ. I’ll give that a go but I’ll order some stainless steel replacement bolts first.

Thanks.

[Luke]

Moustache Man wrote:

Luke wrote:

Hi everyone. I am looking to upgrade the main jets on my GV125. Looked at Mikuni main jets on eBay. There are lots of sellers selling different shapes any types. I know I need a 90 front and 92.5 rear. But which type. Thanks in advance. Luke

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Hi Luke! I have the answer to your question! https://www.wemoto.com/parts/picture/hl-229092_5 Check this link out, look for the code in the title if you dont wanna buy them from WeMoto or if they arent the correct jetting. These should be the right ones, if you search up that code on the internet, you find the specific Mikuni carburettors that are listed in the Specs guide of the GV125 (i did this research myself, you can double check if you like just to be safe) Hope this helps. Cheers

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Thanks for that. I will get them ordered and follow the tutorial to fit them. Fingers crossed it all goes ok.

[Danny]

Hi on my hyosung gt125r 2007 I have a black widow full system exhaust and a k&n air filter with uprated pipes please could you tell me what size jets I need thank you

[♠️ MARCEL]

Danny wrote:

Hi on my hyosung gt125r 2007 I have a black widow full system exhaust and a k&n air filter with uprated pipes please could you tell me what size jets I need thank you

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90 Front and 92.5 rear as mentioned in the the tutorial.  Pilots stay the same. The mixtures don’t need messing with as Koreans already set them uniquely each carb.

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

[Ron]

I have a 2002 GV250 I managed to get the carb off the bike after a lot of yanking, pulling, and twisting. Now it is time to re-install the carb on the bike, any suggestions on how to get it back on the bike given the very small space to work?

[♠️ MARCEL]

Ron wrote:

I have a 2002 GV250 I managed to get the carb off the bike after a lot of yanking, pulling, and twisting. Now it is time to re-install the carb on the bike, any suggestions on how to get it back on the bike given the very small space to work?

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Hey, take a look at this rough topic i just created below

[Tutorial] How to Remove & Re-Install the GV125 Carby | GV250 AirBox

Hope this helps you and look after those intake pipes,  they are now the most difficult parts to get!   (Korea stopped making them)

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

[Ron]

Thanks for the info, carb was removed cleaned, reassembled, and placed back on the bike,one of the hex head screws on the rubber boot was easily stripped out, it took some time getting the screw out but after about 1 hour I got it off. Removing the intake rubber boots made it much easier, by fitting the carb to the air box first then sliding the boots under the carb made it work much better.

[♠️ MARCEL]

Ron wrote:

Thanks for the info, carb was removed cleaned, reassembled, and placed back on the bike,one of the hex head screws on the rubber boot was easily stripped out, it took some time getting the screw out but after about 1 hour I got it off. Removing the intake rubber boots made it much easier, by fitting the carb to the air box first then sliding the boots under the carb made it work much better.

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Glad to hear it’s all worked out now 😉
Ride steady sir!

PS. If you’re ever out in the sun,  post a pic of here on below 😉

Owner's Photography Thread (New Rider? Show off your ride…)

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

[David]

Nice tutorial. But i have to correctyou on one point. On the 2001 gv125 aquila the stock pilot jet is 17.5 and not 15 like you sayed.

[♠️ MARCEL]

David wrote:

Nice tutorial. But i have to correctyou on one point. On the 2001 gv125 aquila the stock pilot jet is 17.5 and not 15 like you sayed.

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Domestically in UK we have stripped them and found them to be size 15 and it seems to match our findings on Korea’s parts database in KR America they use for dealers ,  but it is possible 17.5 is used in other countries anyway.

At the time Euro3 laws came in effect , the newer bikes even had EGR stuff fitted to them (to trick emissions laws) , but at the end, it made bikes a little leaner.  If korea uses 17.5 , they downsize the CO mixture  , if they use 15 pilots , they enrichen the mixture a little bit 😉

Same engine as GT125R bikes , no GT125R bike in world has had 17.5 pilots as they changed to MK2 carbs with jet pumps at the side….   meanwhile GV & GT Naked shared same carb around 2001-2005 with same settings.     GTR bike came much later.

98-01 – GV
2003 – GT
2005 – GTR

😉

I should add that some GV125s in UK started coming with 17.5 pilots again.  Weird if you ask me!

Size 15 seems to be right size pilot ,  i mean  250cc is size 20 it’s perfect for it.  22.5+ etc will just waste fuel .

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

[Darkvader]

Sorry for jumping on this post but i thought i’d share what i’ve found in my carb today. Mine is a 2012 GV125c and has

17.5 pilots with seemingly 82.5 mains.

I was expecting 87.5 but it seems to read like 82.5.

Am i misreading the numbers on the jet?
Thanks Guys.

[♠️ MARCEL]

It is correct , Korea down jetted the bike heavily for emissions control for certain EU countries .

However,  82.5 on a GT bike would surely see its piston rings go pop!

I would definitely recommend the upjetting settings mentioned in the tutorial .   The bike would be a lot better!   (This doesn’t grant you license to use “shorty teeny” slush exhaust cans cause the bike drastically looses speed!)

If you need sound louder than the monstrosity of the single cannon  , you can expand the hole at the can outlet  (get creative!)  but i do have twin exhausts on ebay that are VERYYYYY loud , but work seemly OK as long as the bike is jetted well!

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

[Darkvader]

Thanks marcel, I wasn’t sure if it was mentioned before and i was a little surprised finding such a small jet though i’m also not surprised knowing the emissions people.

I’ll be getting a 85, 87.5 and a 90 pair and playing with some of the settings for the slides as well. it seems that mine from factory had one slide set at 4 and one at 3, i’ve bumped both up by 1 (richer) but that may be a bit much. either way, it starts a load better now i’ve cleaned everything.

I’m not really planning to put a bigger exhaust on the back, i quite like where it’s at currently sound wise. Living in a quiet area i would rather not bring attention to myself, I may put a few small holes in mine if i fancy something a bit funkier, i’ll see :).

[Author]

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