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should be 15 x 1.5mm or 17 x 1.5mm fine pitch but get a thread pitch tool to confirm , because 23mm is an odd spanner size (usually 22mm one side and 24mm next step!)
Welcome, no post is too long!
I will see if i can give you tequila shot style replies ? If i did not make any sense to you, just ask again and I will elaborate for you!
- Thrust Bearing / Cracked or Distorted Plates / Worn Plates / Clutch Basket Attention.
- Find a “DOWTY SEAL” (about 14-15mm hole size) , it does wonders and also “thread tape” (in to the plug itself)
- Clutch and Flywheel will spin a lot to forcing some kind of whirlwind inside crank, on top of the pistons moving up & down , some pressure is OK , as long bike is generally running OK. I would not panic just yet , so moving to #4
- Fuel Related = Does it calm down and pick up speeds OK if you build up the revs slowly ?~
or
Electric Related = Does the dashboard go haywire ? jumping revs ? (regardless if you nurse it or twist throttle fast?)
Need more info on this behavior of #4
my bad , edited. The topics were posted at the same time , had to double check!
Oh my gosh…it could blow up for real??
I wouldn’t panic, but yes bikes can blow up (any motorcycle) , ebikes blow up everyday because chinese keep using crap batteries (just search ebike fires)
On to Hyosung now , it’s just that the fuel tank has a sensor inside has a plug being the same as the starter motor solenoid, so its a case of being careful with which plug is which before pressing “start” (it sends power down there to trigger it)
You got this!
If in doubt , drain the old fuel from tank and clean it out , all that old rust might be collected on the fuel pump, so it is important to double check the fuel pump is OK (or the bike refuses to start as pump is clogged with debris or just jammed) – Fortunately, there is replacement parts at reach on eBay USA , just make sure its new parts first.
There it is, you found another source of power loss , no baffle means the bike will lose too much torque at the lower revs , it has to scream more to get going
I gurantee you. a baffle inside a 125cc will make more power than without , and you can even test this yourself , the vtwins make peak power around 7k-10k rpm (pointless revving past 11k rpm as that’s a sure way to cook the engine)
Measure the hole , and find any baffle that will fit in there, make sure the baffle can be modified so that “gas fumes” exit the bike at a 10p coin size hole (get creative) (10p coin is 24 mm (0.25 cm approx) yes that small , and it will still hit 70+ if tuned right.
Factory GT125R has an oem exhaust with a lot of restrictions but still managed to do 82mph indicated (ish) , this is factory. So ignore anyone that advises running without baffle is better (unless they want hearing aids faster lol) , it is still loud baffled on aftermarket cans.
Lextek OP1 and Black Widow FULL Size cans are my recommendations and what i use on all bikes, since they are also road legal & pass MOT with no issues on noises. Others are HAWK Hyosung Exhausts , 2 Brothers USA (may need baffle!) , MTC UK (baffle it hard) , Scorpion Hyosung Exhaust.
The 1st two i mentioned are just my persona pics. Hell a full size micron isn’t too bad! – any can is OK as long as it doesn’t fail your MOT & isn’t a “shortie – midget! ” , hyosungs hate midget cans . Even more so on a GV125 Cruiser (it literally looses like 70% of its power if it senses midget cans added to it) , i had to put the OEM one back for the customer and it’s been happier since.
Man, i heard about the crazy weather over there , we felt some bit of it here in England! (we are across the ocean from the US!)
I hope you and your family are alright and It is good to see that hasn’t stopped you enjoying bike life , sometimes its just better to go and unwind from the madness!It looks so dark in there, i can’t tell if the baffle is even there , it looks like its baffle-less. ? I could be wrong , take a picture of that hole with camera flash ?
Sorry i delayed.
Will need pictures from you and it must be clear for all to see , if a wire is not visible in the picture, then its hard.
Also it helps to mention something like this:
1. Found this plug (with supporting picture)
2. here is the exact wire colours
3. This plug was under the fork = We will tell you it is for a speed sensor etc.Just to give you an idea – Have a look at the top of the site and click “shop” link, there 3 parts i would do right away:
- Carb Gasket Rebuild Kit
- Oil Filter
- Air Filter
Then follow this tutorial for oil change
[Tutorial] How to Change Oil & Filter on Hyosung GV + GT125/250 +R
Then follow this tutorial for airbox removal (it is very hard if unsure what you are doing), the “intake pipes” are not made anymore and are very very rare and expensive to acquire , i couldn’t stress this part.
Here is one from me
[Tutorial] How to Remove & Re-Install the GV125 Carby | GV250 AirBox
Here is the alternative for another member
[Guide] Intake boot manifold removal GV125C / GV250 Carby (Air Box Tutorial)
Then ofcourse like any motorcycle, these should be checked
- New Spark Plugs (CR8E as per OEM Hyosung)
- Ignition Coils Rust (it happens)
- “HT CAPS” that hold the spark plugs (very recommended to use NGK ones, as the old style OEM Hyosung black caps crack & leak sparks!)
Ensure you have good jets and good correct sizes, this topic below should help
[Tutorial] How to swap Carb Main Jets – Hyosung GV & GT 125/250
Clutch Overhaul
[Tutorial] Hyosung GV/GT 125 & 250 Clutch Plates Replacement How To
Fuel Pipes and vacuum pipes (GT250 and GV250 use the same carbs)
How to change Vacuum Lines on Hyosung GT125R GT250R & GT Comet (Air Hose Diagram)
As you browse more and more on the forum, you will need a cup of tea but all knowledge by other members will do wonders for your winter projects 🙂
Welcome!
How cold does it get over there?
In winter , if its sunny, go ride with some warm clothes 😉 , just make sure you have VERY good tyres as i know where i live in UK , the roads can be icy!
Hello & welcome Bianca ,
The manual section says GT & GV EFi for the 250cc, they are the same engine (with some slight differences to parts based on the year)
Don’t give up on it. I think you will like it when it gets going! – Another backup source for manuals is MANUALSLIB website (Manuals-Lib is what they are called)
I will upload more on the forum when I can.
If you can fix the Hyosung yourself, you will pay less at the garage anyway for simpler tasks even if you apply the same logic on your other bikes.
Hey Bianca,
Not to worry, if that unit is working, then that’s good.
- Open the rider’s seat and remove the side plastic covers hiding the battery.
- Go behind the rear engine exhaust …. (it has 2 engines, so go to the back facing engine and look at the exhaust pipe area where the clutch cable ends up.
- There is a metal plate that is attached to the frame and the metal plate has 2 hooks on it.
- These 2 hooks are facing the plastic battery try.
Found it ?
- The solenoid has a rubber cover ..,. put it inside the rubber cover like this

- After that, look for the 2 slits on the sides of the rubber cover….. like below:
The space between the plastic battery tray and the metal plate with hooks is very narrow, so i would carefully take your time and slot it in.
Done?
Find a 2-pin plug (on the bike harness) that’s exactly the same as the fashion as the solenoid itself (ie. male connector going to the female slot) and the wire colours “must” be identical.
There is another plug that is for the FUEL TANK sensor (so becareful not to plug the wrong wire!) , if you press start , you might blow up!
Thankfully Hyosung has made sure the FUEL sensor plug has different wire colours to the plug for the STARTING SOLENOID
This next step is connecting it to the battery and starter motor, so excercise caution.
- Remove battery first!
- Red wire from the battery (the thickest part) goes to one side of the solenoid and screw it tight using it’s own nuts at the top of it.
- The Starter Motor itself has 1 single thick strong wire that goes to the opposite side of the starter solenoid.
Double check everything!
Then connect the battery and test when it is safe to do so.
Hope that helps.
2 inches = Hole Size (where exhaust fumes come out of ?) or just the side ways length of it ? I was on about the hole size.
90 & 92.5 is the absolute max and probably the best way.
The bike pulls better with the baffle (find a way to make the “HOLE” of the baffle about the size of a 10p coin)
Hello, I saw your post earlier and responded to it, but you can always update here as ill watch this topic now.
This mod is free and does wonders on the bike!
[Tutorial] How to adjust Carb Slide Needle (Tuning) – Hyosung GV & GT 125/250
Pilots = Size 15 is a good downsize , simply because the factory 17.5 is a bit too big
Mains = Depends what exhaust you have (upload a picture please)
Regards
23mm is the size for the nut :- )
The shop! 😉
All good, clutch plates we can sort that for you no problem and plus oil filter!
Everyday bike is a good way of keeping it alive, better used than stood still in a barn to be fair,
I would say make sure you have some good michelin rubbers for them icy days!
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