♠️ M77
Forum Replies Created
-
Posts
-
Remove the airbox carefully and inspect the throttle body O-RING (There is an O Ring which connects the metal bodies to the plastic airbox incase of any leaks caused by a stone/dirt ingress somewhere ?
The crack you see there, can you shine a torch through it for any possible pin-hole gaps ? – find some kind of tiger glue seal to patch that area and see if that helped ?
I’ve not seen that before, did the bike fall and airbox got warped? or did something hit it ? that should not happen right in the middle where throttle bodies are exposed, also while the throttle bodies are out, use carb cleaner to clean it (not the plastic sensors or plastic airbox!)
Sensors on the throttle body = Only use contact cleaner to clean the connector sockets. Helps improve signals to the ECU for a smoother throttle response
Hope that helps!
Hey, this sounds like extra hassle but i hope you don’t mind it, remove the whole flywheel.
I had this issue with a customer bike in the UK that was a 125cc variant, the bottom crank shaft had 2 missing teeth which was a known for certain engine batches, so the chain was never fully wrapped around and didn’t run right, eventually the front cam shaft snapped in half.
So have a look at the bottom crank teeth where the chain rolls and confirm it all looks good and healthy ?
If so, do you want to chance a replacement cam chain and cam shafts and tensioner ?
Take a look at the tensioner Belts (the plastic guides that slide the chain , including the top metal triangle which has a plastic buffer that gives the chain some little downward tension also)
It’s a good job you have sharp ears and eyes, it could have been worse and fortunately it sounds like either the chain or the tensioner need a replacement (IF the crank teeth are OK or the cam shaft Teeth are also OK? – giving the sprockets no-reason to jump the chains at high speed)
You’re lucky, a single chain bounce out of the sprocket, over here means were are rebuilding a snapped engine🤕🩼
Let us know what you find!
Thank you so much for the help and for taking the time to write out such a clear, step-by-step guide! I am really sorry for the late reply in getting back to you. Just wanted to let you know that I actually managed to get them changed already. This detailed breakdown of the 3-piston caliper and the warning about the CBS rear brake pedal is super useful anyway, and it’s great to have it on the forum for reference. Thanks again!
You are welcome! Glad you got it sorted 🙂
Dont ditch the box, here is the help guides below
[How to Tutorial] How to Remove & Re-Install the GV125 Carby | GV250 AirBox (Alternative Guide)
[How to Tutorial] Intake Boot Manifold / Air Box Removal GV125 & GV250 Carby
We have been calling these calipers TCTC even our dealers say its a TCTC caliper , so thank you for confirming its true Domestic name 🙂 , normally when i look at the calipers , it says TC_TC , but i dont see TC_IC ,
Other riders have sold the wholesale website or others have been scammy lately , so it is suspicious why they banned South Korea.
Check ebay ? There is a few used calipers there now , even eBay USA (.com) or eBay UK (.co.uk)
That is crazy!
Okay, hmmm, what if you get 2007-2016 Forks ===> it means you can use TCTC calipers , but it also means you will use 2007 mudguard , 2007 7.6 inch headlight etc, as the 2001 and 2007+ models have a front facelift look, not just a fork upgrade.
Could use a spare nut from a DIY store that fits (i forgot the size) , as a temp measure to get back on the road, until you both find ways to fix the actual issues or patiently wait for a replacement used float to show up on fleebay
What rubber pipes and o rings do you mean?
Pipes = Sorry i meant the intake manifolds (which hold the carbs down to the cylinder heads) , so they also have o-rings in them, so if one of them got deformed during re-install or are too old , you could have a micro leak that has made the vacuum system weaker. Also make sure both front and rear intake pipe share vacuum to open the fuel pump. (2 intake pipes feeding the vacuum pump in a shared T-Junction (T-Piece) = better chance of fuel flow)
If you see any egr parts (ais parts) get rid of it, your vacuum system will thank you, look here:
[How to Tutorial] AIS Removal Guide – Hyosung GV125 GV125C (EGR Blank Kit Fitting Guide)
This sounds crazy but have you seen the tutorials on the forum on how to carefully remove the airbox , then you can access the carbs to give them a much needed ultrasonic clean
Then check what jet sizes are still in the carb ? Also we don’t know if the float needles are still working properly , these floats control how much fuel you can get , if it gets too low before the pump can send more fuel, you will feel like its running on a dry tank then cuts out. It wont start until you crank it multiple times , then it works (cranking was filling up the carbs again)
So maybe our next battle should be the carbs
Good job replacing everything else, it just means you are serious about giving it more life , some people just abandon it which is a shame. From what you said, it sounds like we should deal with the carbs and also double check the rubber pipes for any damage and replace O-RINGS which sit inside the rubber pipes
DSG is no longer around, but… i personally would see if i can get a spare caliper from the RT125 or RX125 (old models) that also have a DSG caliper too, because the OLD GV`125 (before 2004) was using a flat disc from the RT125 if my memory is correct.
If not, to use a TCTC caliper, be ready to fabricate or modify bracket to fit it.
Hyosung stopped making it that is why, but is there a way you can remove the piston , measure it or take it to a local bike shop so they match it from a different bike?
Technically, you CAN fit another caliper of similar size (maybe old 80s suzuki 125? ) and fabricate a custom bracket to mount it ?
I was going to say it is the gold nut that usually has the O-RING , the silver plunger has a spring to it.
So focus on the gold nut to seal, unless its leaking through the actual silver rod (would be odd if it did)
Unscrew it, and place a fuel safe o-ring from a local shop like halfords or something, there is an O-ring usually as it is just a plunger that only squirts a bit more fuel on 0-1/4 throttle twists. Not critical as GV Aquilas or older GT Nakeds never had it , it’s a GTR thing.
And sure here is the diagram (Press and hold to save image to phone or PC) – You won’t always see the plunger as the diagrams still used the 1st generation carb floats
Sorry for delayed reply, but since one was not made, I will use your topic to make my reply as a tutorial if it helps others too (add your replies with pictures if you get stuck!).
Step-by-Step Guide: Hyosung GV125S EFI Front Brake Pad Replacement (and CBS Care)
Since there isn’t a dedicated guide on the forum yet, here is a complete walkthrough for the GV125S. It is a very manageable DIY job, but because it uses a Combined Braking System (CBS), there are a few unique quirks you need to watch out for.
Tools and Supplies Needed:
- New brake pads (which you have ordered of course)
- Socket set & strong allen keys that wont round off (for caliper bolts)
- Flathead screwdriver / small spanner (it helps pry things off incase they have been jammed by miles and miles of road dirt)
- Brake cleaner spray and an old toothbrush
- Silicone or copper grease
- A small block of wood or a G-clamp
1. Removing the Caliper and Pads
- Locate the two main bolts securing the front caliper to the fork leg. Loosen and remove them.
- Slide the caliper off the disc. Do not let it hang by the rubber hoses—use a bungee cord or zip-tie to tie it to the frame, mudguard, or steering bar, or let it sit on top of a tiny table.
- On the bottom front of the caliper, you will see a small “mini” blanking nut. Unscrew this to reveal the threaded sliding pin hiding underneath it.
- Unscrew and completely remove this internal sliding pin. The old brake pads will now slide right out.
2. Managing the 3-Piston Caliper & CBS (Crucial Step!)
The GV125S features a 3-piston front caliper because of the linked CBS setup (where the rear brake pedal also activates the front pistons).
- ⚠️ Golden Rule: Do not touch the rear brake pedal while your front caliper is off. Because the fluid lines are linked, pumping the rear pedal will instantly shoot the front pistons right out of their bores, spilling fluid everywhere.
- Cleaning the Pistons: Before forcing the three pistons back into the caliper to make room for thick new pads, they must be clean. Spray them down with brake cleaner and scrub off all road grime with an old toothbrush. If you push them back in while dirty, you will drag corrosive road grit straight past the delicate rubber seals, causing the caliper to seize up later.
- Pushing them back: Use a flat piece of wood or an old brake pad across the pistons to push them back evenly and slowly. Keep an eye on your front master cylinder reservoir to ensure fluid doesn’t overflow (We don’t know if a garage previously put too much fluid when they serviced the bike brakes before you came along. Don’t forget the GV125-S EFi has been out since 2018, so we have older models that were likely re-serviced with new brake fluid previously. It is wise to make sure it gets a fresh fluid flush every 4 years, but this is more of an advanced job for another time—if your bike is a 2023 model and it is 2026 today, then you likely have 1 year before Hyosung mandates the lines get replaced and fresh fluid. But I digress!).
3. Reassembly & The “Hyosung Brakes Rust” Check
- Take your sliding pin and give it a thorough clean. Apply a very thin smear of silicone or copper grease to the smooth shaft of the pin. Do not get grease on the brake-pad friction material!
- Drop the new pads into place, slide the greased pin back through, and tighten it down. Replace the mini blanking nut.
- Mount the caliper back onto the fork leg and torque down the two main bolts. Make sure it is tight so the caliper doesn’t fly off when applying brakes during a ride. If in doubt, get a small torque wrench and use a setting of around 15-20 ft-lbs (or roughly 20-27 Nm) to tighten the bolts until it clicks.
- Pump the front brake lever a few times until it feels firm. This resets the pistons against the new pads.
Casual afterthought: While you are doing this, inspect the condition of your original fasteners. Hyosung pins and caliper bolts are notorious for rotting, rusting, and seizing up in UK weather. We actually keep full stainless steel hardware kits down at our shop specifically for these GV125S models to stop them from ever seizing up again—just browse the shop if you ever need a set down the line!
🔍 While You’re There: Don’t Forget the Rear System!
Since you are working on linked brakes, it is highly recommended to do a quick health check on the rear setup at the same time:
- Check the Rear Master Cylinder: Because of how the GV125S is designed, the rear master cylinder sits quite low down and is highly exposed to road grit, salt, and water. Give it a visual check for any weeping fluid or accumulated crud.
- Do You Need to Change Rear Pads Too? Front and rear pads wear at completely different rates (usually fronts wear out faster, but CBS can balance that out depending on your riding style). You don’t need to change them at the same time, but you must check them.
- The Easy Rear Visual Check: Luckily, the rear caliper sits openly in the middle of the top of the rear brake disc. You don’t even need to take it off to inspect it. Get a torch, look into the back of the caliper, and check the thickness of the remaining friction material against your brand-new front pads. If they are getting down to less than 2mm, swap them out next.
Hope this helps! Keep us posted below if you have other braking questions!
Safe braking!
Ahh okay , i got you.
For each nipple, hyosung puts a clear cap called “Airbox Oil Catch Tank Cap” like you see #6-7 below
However it is not a part easily obtained on its own, so grab a clear hose and clamp it there , then block the other end of the hose and clamp it.
At least both holes will tell you if there is oil deposits inside the clear tubes (about 4cm long max is good enough)
Regards
The black large pipes on your carb = They go to the road (0verflow / breather) For general tutorial for routing fuel lines , see below
[How to Tutorial] Upgrade Fuel Lines & Filter on Hyosung GT GT125R GT250R (Carb Hose Diagram)
Hi again i cant find hose connection this topic
Hello,
I am not sure I follow you ? The link is showing the tutorial how to connect fuel pipes from the Tank to the PUMP , then the carb
Your picture = Ignore the black pipe that is sticking out of the carb, just point it towards the ground (road)
It would be a wiring issue, the “start” button is what triggers the relay circuit but not every Hyosung model has a relay connected to the CDI (carby) or ECU (efi)
But i know that in my EFi experience , the relay does not click whatsoever if the ECU thinks the bike has a fault or the clutch switch is dead (replace, dont bypass) or the kickstand switch Bypass has corroded (check again the Kickstand bypass wires under the tape did not corrode) = These turn the relay off even on later carb models.
If its wiring, follow the wiring from the start button to the relay and ECU, then see if there is any reason the signal could get weak, perhaps too much resistance in the connectors (if the pins got too oxidized, we use contact cleaner to improve the situation, then there is enough signal / power along the lines to finally trigger the relay by the “start” button)
Bypassing the relay is forcing the starter motor to spin the magneto flywheel, and the ECU gets the pickup coil signals and is forced to fire up immediately (sort of like a push start) if all other sensors didn’t throw an error code stopping the ECU
If the ECU primes the fuel pump, it generally suggests its priming to fire up now. I know from experience my Delphi ECU will NOT prime the pump if i so much have a neutral switch not working! (It thinks i am still in gear)
The black large pipes on your carb = They go to the road (0verflow / breather)
For general tutorial for routing fuel lines , see below
[How to Tutorial] Upgrade Fuel Lines & Filter on Hyosung GT GT125R GT250R (Carb Hose Diagram)
It is possible that you may need a new relay or the battery is too old ?
Have you tried OXFORD NAV BAG / BAFFALO NAV BAG ? this straps to the yoke itself , and you can see your phone or satnav as clear the dashboard too, i use it sometimes on the GTR when i am not on the GV Cruiser.
Not much room around the bars because anything else will hit the fairing screens when turning and they tend to vibrate like crazy, i never trust it.
Or, buy a SPARE Hyosung steering nut, go to a bike shop, to make a hole in it , and you can look at doing RAM mounts (many variations on Amazon US store, so have try one that fits you)
If not, i usually sometimes also chuck the phone in the bag, and rely on bluetooth earpieces in my helmet.
Welcome to the club and nice ride! – Yes they still make 650s , their latest is the GV650 Pro ABS , the GT650 was last made in 2016-2020 era (no news on revision of the GT250 and GT650 yet)
Keep the GT250R , it’s a nice little rocket! – very rare to find one that clean these days!
