♠️ M77
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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! ⚠️🔥) 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)
The cheapest “premium” chinese can you can get that is GOOD (personally the only china can i like) is LEXTEK 350mm exhaust , go to Lextek’s website and get their 350-450mm exhausts (the longer the better)
Man that is a CLEAAAAAAAAANNNNNNNn bike, don’t drop her! Wow.
Good question on lights, personally leave it Halogen , 99% of LED lights are china made and ofcourse they won’t fit as their heads are too bulky for the GTR shells.
Until Osram & Philips the 2 top EU brands of bulb makers invent a road certified LED for bikes, i would stick with halogen. They do make LED for certain cars (ie. Audi R8) but on bikes there is no LED bulbs for them yet. Sometimes the chinese LED’s are “bright and glaring” , you want a light that is brighter but not painful to your oncoming road users
Get Osram Nightbreaker LASER and Philips Xtreme Vision bulbs , these are the peak of the halogen tech.
Hey , upload a photo here as a test , there should be a bright yellow box above the reply box showing a tutorial link for picture uploads.
And show us the exhaust in particular ?
EFI bikes need a balance: sound + performance.
Instead of a very short “straight through” muffler:
Look for a slip-on designed for EFI bikes, tuned to maintain some backpressure while increasing volume.
Some aftermarket mufflers give a nice growl without killing midrange torque.
Avoid removing DB killers entirely. Some aftermarket options include removable baffles for track-only use.In other words , as i have leaned over the years Black Widow Exhausts that are 400mm always gave the best sound and balance or Lextek OP1 350m long cans . EFI bikes need some backpressure—super short slip-ons can make them run lean and lose midrange torque. Keep a DB killer and use an EFI-friendly slip-on: louder sound without killing performance. Those fake akras are just “annoying” loud , but a proper slip on from the likes of Black Widow , 2Brothers USA (rare) , MTC , HAWK in my own experience have been excellent.
I also modified the baffle so that the overal hole size is about the size of a 10p british coin (forgot dimensions) , as an exit-hole too big in the DB killer meant it felt “flat” riding it , but too narrow is not good either. I experimented a lot , though my old previous bike was the Kawasaki ZZR400 , it did not care what exhaust it had (for the most part) as it makes its power much higher up (screaming inline 4!) , the twins on Hyosungs both GTs and GVs i own really prefer the torque at the early revs not to be disturbed , the GV was more frustrating but i am digressing.
The stock cans on all hyos are too heavy! – You could get a tiny acceleration gain (very tiny) but shaving off the weight by switching to”road legal , performance exhausts” , if it helps check ebay UK and find BSAU stamped exhausts (BSAU generally meaning for road use) but just loud enough to get noticed! – In UK , if an exhaust is too loud , the inspectors (MOT Test) will fail the bike if the guy hates it and issues papers to the owner to change it (before he can ride on the road legally again) we have to get our bikes checked every 12 months to make sure the bike is “road worthy” , but exhaust noise is just one of them, though some harleys are very loud and still get away with but i am digressing , its 10pm as i write this haha, i think my brain is going 😔
Hope my un-organized reply helps ?
use the carb version of the GT250 / GV250 manual for engine clearances and its internals
For EFi parts, take a look here:
Also , check the 650 manuals , (some , i mean SOME, efi parts are shared between the 650 and 250) , I uploaded a lot of 650 EFi manuals.
Welcome!
Hope you put enough miles on her this summer and what are you future plans with it?
Share a picture of her if you want!
Like you i was part of the 4 wheel world but i had more better friendships with my 2 wheeler buddies and i feel more free (although i wish England had summer all year long lol)
Sounds like you have regulator issues and stator issues (both have their own independent issues (ie. Reg is probably under/overcharging at low and high revs which affects more sensetive parts like the sensors all over the bike and the ECU or the stator itself has an output that is either too high or too low. So have a look at the topic below and confirm with numbers what state your charging system is ?
Rectifier – How to Test Stator , Battery , Regulator – GT125R Carby
Ignore that it says Gt125R , the principal is the same for GT250.
If you can verify the charging system or fixed the charging system has gone stable now, then go for a longer ride (but carry a spare battery safely incase you need to swap it if heaven forbid you get stranded)
The general idea is to put the bike under some real world load to assess how its performing etc
Thanks,
On my first go, I think the float stuck as it wouldn’t go then gas came out the overflow. Tore it down again then used your suggestion and with some tweeking I have it running reasonably well. I’m letting it sit and will see how it behaves tomorrow.
It’s not a bad idea to go through everything once more , good job!
Mix screws generally on that bike start 1 full turn from seated or 1.5 and see how it behaves?
They produce it on the spot but exact details will be confirmee by the garage
Alternative Option!
If for whatever reason you are not able to use the forum’s own image uploader , then follow the instructions below to upload your images elsewhere so you can link them on to this forum:
At least if you upload to a place like POSTIMAGES.ORG which allows free image uploads, all you need to do is then copy the [BBCODES]
Then write your forum topic like this below:
This is an example post with a picture and the picture is below:
[BBCODE] <— image will actually appear inside this bbcode don’t worryStartright Motorcycles in Leeds sell the restrictor kits or they will fabricate it for you and make it “official” , just tell them we sent you.
If not, it is possible for your local garage to grab the SV650 kits and try to retrofit them to the Hyosung throttle bodies and give it the “garage stamp” if insurance ever asks for it
But generally I have not heard much about it being an issue riding full power the riders did have A2 but were much much older folk who ride sub 400cc bikes for years , so they just went full whack (yes strange enough I did hear about older riders staying on A2 because they find riding beyond 700cc useless for street use)
For you , you can still make yours A2 compliant , if the Hyosung kits are not there from Startright Motorcycles , then its closest cousin would be the SV650 (Well Hyosung Korea did get involved making the engines or its parts in the past for suzuki) so should make life a bit easier to retrofit some kits.
Really its just restricting the throttle output that’s all!
