â™ ï¸ M77
Forum Replies Created
-
Posts
-
Those sprockets are well overdue! They are starting to look like hooks.  Wow. You definitely used them hard 😉
Yes a full replacement is advised but this time email us for an X Ring option as I have not added it to the site yet.
Also as per Hyosung manuals. Replace clutch plates every 4-6k miles otherwise your clutch will start to affect your gearbox but this is just advise as I dont know when your clutch was replaced.
Dang that red looks sweet!
Indeed it does!
Hey,
I would drop down to 13T , 14T is too heavy for it. I almost never use 14T when i do 520 conversions. As you have 428 , i do not know what tooth count of rear sprocket to comment further, this could contribute to speed issues. 67MPH is usually the factory speed but here in UK National speed is 70mph and that is even dangerous for some riders as cars normally drive to 80mph + all day long, hence the need for a longer gear rear sprocket but also quicker small front sprocket , so you have to experiment with ratios that suit you.
Clutch Plates = Some minor HP loss happens if springs are heat fatigued & plates are too worn down ? = Less HP transfered to back wheel, so it is possible that it may contribute to your vmax issue.
Intake System = Connect the carbs to the airbox first ====> then tighten nicely.
Now your carbs and airbox are fully sealed up.
This means you have one big piece (carb+airbox) going down to the intake pipes connecting the engine.
Be VERY cautious as it is getting harder & harder everyday to get good condition rubber parts and they are very delicate things.
Is it possible to take a picture of the manual and upload it here ? And also show us your footpeg area to see what they mean by that.
In the past , i basically used universal pannier kits (was cheaper) but were hard shells which I needed and also got a universal rack kit that mounts to the sides of the grab rails along the rear pillion area. I just had to get creative and swear a lot to make things fit! This was on a bigger older GV (carb ) , personally I have not fitted one to a GV125-S, however Hyosung did not change any structural parts for the footrests since 2018-2025
The major change in 2024/2025 is their new model called GV-125X (X) , totally looks different. S-models will remain S-models without much change visually to be fair
The worst is that you could end up getting a metal plate fabricated to get around fitting the boxes or return it but i would also email or contact Shad themselves.
They are an OK company (quality wise), personally I use their Click-Lock tank bag systems, but as for customer support I can’t comment as i never had to bother them about any issues i had personally with their products.
Keep us posted!
Can you also upload a picture of the front sprocket and rear sprocket please? so we can see the close up of their teeth , then I will have better advise if it wise to replace just the chain or not.
general consensus is that a chain should be replaced with the sprocket , but because it is a 125 running on a 520 sprocket, you “may not” need a rear sprocket yet but the front sprocket is more critical as it wears down much much faster.
Also report how many miles you have done and what chain lube do you use ? how often do you lube it ?
Sometimes not lubing the chain after it rains , makes it wear out a lot faster , it’s just how mother nature is vs naked moving parts.
If you do a LOT of miles every day, I could do you an X-Ring chain next time but we can discuss that privately via email.
For now, just show us here what your sprocket teeth look like and report back “miles , lube product , how often etc.”
Try to tap in a socket in to the bolt and nut on both sides , get the impact socket, and use a breaker bar instead ?
Those frame bolts will turn to cheese , so be ready to replace them, it sounds like it was rusted in ? (owner not expecting to remove the engine but rode through mud & salt so much that anything not stainless gets seized in terms of bolts. Copper grease advised when refitting critical stuff!
Attack them tactfully as they round off easily but i took out the worst ones with breaker bar + a black impact socket
Not myself personally but I don’t have any further comments without more pictures of your situation to advise further.
Sounds like you just need to copy the old parts & old harness layout over to the new stuff etc , but yes sometimes Hyosung adds extra stuff on later models without notice.
probably means Fi light was flashing ? You may be getting a sequence flash ie,
Fi light blinks in a sequence = 5 blinks , pause , 6 blinks , pause , 7 blinks  (it repeats itself)
567 code = could mean EFi system thinks battery is too low to power everything on it especially the pump too.  (code 567 is just an example)
If its not that, go to the 650 manuals section of this forum and download the service manual that matches your bike (Daewoo Korea ECU or Mitsubishi Japan i am guessing based on 2010)  , the manual will show you how to read the flashing sequence.
The dash could say “Fi / 0 / Fi / 0 ” but also test your stator using this guide below and tell us the ohms
(ignore that it says 125cc, the principal is the same)Rectifier – How to Test Stator , Battery , Regulator – GT125R Carby
get ohm readings for the coils that spark your plugs and HT caps too , tell us
if you have extra time, drain oil nicely ==> Remove the stator cover slowly as not to rip the gasket that may get stuck to the engine crank, and see if the stator is burnt out.
if in doubt, upload some pictures here.
Upload a picture of your spark plugs on the forum so we can see what is happening if you can.
Sometimes black smoke means you’re too rich or there is air starvation on the bike.
Personally i have not used it and would never use it, there has been a lot of people complaining about its “scammy” behavior and if you do get lucky, some parts are missing etc. So use caution.
If not, buy a wrecked engine in your country or a wrecked hyosung bike and take its engine.
All the hyosung’s i’ve owned and fixed customer bikes , i tend to find the 2pin version does the same job in fairness, i never had any issue where the bike had 4 wires on the harness and a bullet connector , I used a 2Pin version that was chinese as that’s all the local supplier had at the time. Otherwise you may have to check eBay AU for the official used one from places like QLDmotorcyclebreakers (i can’t remember their name at all , but it had QLD at the start, i was getting an airbox to restore a bike in UK)
Yes add the picture as Hyosung made 2 variations of the GV125 EFi ECU’s , they may have updated it again for 2025 onwards but could still be V2 type.
Anyway, have a look at this thread and see if you can investigate your ISCV unit to maintain the idle.
GV125s idle speed when hot / ISCV problem (Idle Speed Control)
if it starts , the ECU still has some life left, so i wouldn’t say it is completely toast.
That silver metal bracket is used on GV250 EFi and Carby.
Ignore those 2 holes. It is for “idle adjuster cable hook” for carb models.
Hello, it is the correct size 11 54 11 as that’s what is sold and used in the UK , i personally not heard any reports on our soil such seals being missized.
if the odd 53 size came on your forks (i wonder why!) , try to get that 53 size in your local seal stores. There will be something that uses a 53mm tube for hydraulics but i don’t have a reference to point to.
That NGK part number seems to suggest also a 45mm seal used on Suzuki 200cc bikes , but can’t trust Google 100%
Piston rings = Working on it as i myself want to stock them , hyosung is not making anymore pistons for carby bikes, as they moved on to the GV125-S EFi now (totally different engine)
Cylinders = check ebay , if you don’t see damage on yours , then ignore that but usually ask the sellers on ebay if the jugs are OK , personally i stripped some jugs off several bikes on ebay and most are untested as the engines had other bottom end issues (bad crank bearings etc) but i could not see anything on the jugs that would cause issues later so i listed them as spares / repairs , you could buy the cheapest jugs , send them to a garage to get them re-honed , buffed up or do it yourself so its super smooth.
Pistons = Best bet is to get the used ones , they will have rings you can take from. or use the pistons.
Valve Heads = Get ones that are said to be OK on ebay, saves you having to replace bent valves on yours if its causing compression issues.
Tear down first and see what’s going on with yours , if you ever put it back together , new-gaskets are a must!
Replacement engine is a last resort , don’t give up on her, you just found out the true reason why it struggled to start , the ex-keepers need a slap for abusing it.
If you’re looking at the parts on ebay , i would just get spare pistons too. Least you can use the piston (incase yours is damaged) or take its rings to see if improves your older one. Cylinder Jugs = Justincase yours may be scored up inside causing compression loss
Cylinder Heads (valve heads) is just incase you want use newer / less mileage heads.Or possibly look in to replacing the whole engine if the labour is too much from your garages or if you don’t feel like doing it yourself. Garages have their own rates so i can’t estimate labour rates , you have to shop around.
It would be wise to remove the engine off the frame to do it all properly as its very awkward to do it while its inside the frame but you can, just very awkward, so it might test your patience or higher chance of making mistakes (ie. screw fell inside the engine!)
From the horse’s mouth , it says 250 but same thing.
https://www.manualslib.com/manual/865104/Hyosung-Aquila-250.html?page=36#manual
Shit! , okay i hate to be the guy to tell you that you will definitely need to get some spare pistons on ebay and CYLINDERS (both piston jugs and valves head)
Take the 2 heads off , replace them , also use new gaskets! – Your compression is too low hence it just struggles to maintain idle. It should be 125 psi “minimum” to get going but not ideal , and around 140+ , you have a ride-able bike. If its 175 psi that’s like a new bike.
Damn, now we can see why its been fighting and coughing a lot. The front barely got warm , and it is the one with the weakest compression.
Try this one (tap here) , I will update the forum, thanks for the headsup!
Hmm in Spain, go find this bottle (this exact bottle) and get 2 of them (yes 2 of them)
https://www.halfords.com/motoring/engine-oils-and-fluids/fuel-and-oil-additives/wynns-formula-gold-petrol-treatment-500ml-166754.htmlDrive with both bottles filled in the tank and also about half a tank of E5 fuel (5% ethanol? here it’s called premium fuel in UK) as the cheap ones (standard fuel) %10+ ethanol is just not good on Hyosungs , although it will run E10 fine but nothing positive for any vehicle using too much ethanol but i am digressing.
Observe her, the idea is to try clean out your entire fuel system critically the pump and the injector. I know myself that when i increase the throttle, the pump gets louder , what if your fuel pump has some kind mini-delay to the throttle response or the injectors are waning ? TPS would be the last thing we check but it is also worth checking to make sure it is in OEM specs with your multi meter as per manual guidance.
If the tank is nearly empty, siphon the fuel out of the tank carefully, and inspect your fuel pump or the fuel strainer being clogged, it gets clogged eventually causing the pump to work harder than it needs to or slightly less pressured fuel going to the injectors.
Least if the 2 bottles get used on the tank, its one less maintenance thing to do knowing you had the bottles try to clean out the fuel parts.
Another tip , spray carb cleaner (be wise! âš ï¸ðŸ”¥) around the intake pipes , so see if there is an air leak (even a tiny bit) , these O-Rings eventually do need replacing to keep things optimal:
Intake Pipe O-RING (Inlet Boot Seals) x2 – GV125 GT125 RX125 GV250 GT250 Hyosung
Also , check your ISCV O-ring on the airbox, like this example below:
GV125s idle speed when hot / ISCV problem (Idle Speed Control)
