â ď¸ M77
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Check your TPS using the service manual and don’t forget to to make sure the fuel injectors have been cleaned with an in-tank cleaner such as “Wynns Formula Gold Petrol” or a similar product in your country.
Hmm, if you don’t mind at all, have a listen one more time and with an auxilary cup tank to drip feed fuel to the fuel pump, as we need the big tank out of the way.
Go around the bike as much as you can and get your ear as close as possible to all areas of the engine, find the location where it is making the most of these noises and 1 last picture with your finger showing where the noise is the loudest ?
It’s a good thing the clutch plates and springs are OK.  Sometimes it can be the thrust bearing that sits inside the front cover of the clutch plates, it spins nonstop even in neutral, so you want to be sure the needle bearing is OK. Get a VERNIER caliper, measure thickness of your plates (if the engine clutch cover is apart, the manual mentions to check thickness of the friction plates before deciding a pro-active change before last minute issues in the future, your gearbox will love you for it.
In regards to valve clearances, you could get a feeler-gauge , open the valve tops off on a cold morning, before it even starts , follow the service manual to spin the crank a few times then place the feeler gauge under the cam lobes to get clearance values , feel free to report them here , at least you will know yourself some hard numbers before it needs stripping down to change the shim-tappets
Check manualsLIB website or contact your dealer, they will give it to you, or check KR-MOTORS website (Hyosung Official website), click their GV300S bike models , and they should have a page that says âmanualsâ Some one on the forum has already done valve clearances tutorial on their GV300S , if you search for it
Searched KR motors website and manualslib, no service manual exists for this bike.
Get in touch with your dealer, they will get it from the importer who imported the bike in your country, you won’t be the only Hyosung rider with a GV300S , your country is also having a GV250-DRA imported , so the importers must have manuals to give dealers to fix the bikes on servicing , a physical copy is very handy! – Give it a try
I will try to hunt it down and upload it to the site soon.Check manualsLIB website or contact your dealer, they will give it to you,  or check KR-MOTORS website (Hyosung Official website), click their GV300S bike models , and they should have a page that says “manuals”
Some one on the forum has already done valve clearances tutorial on their GV300S , if you search for it
No need to upgrade the oil pump, changing to 25o cooler is the #1 engine mod for the 125cc , your rear cylinder will thank you!
Front cylinder not a problem as it gets a lot of air anyway.
Sprockets, try a 520 chain conversion kit  (52T on a 428 chain rear wheel is too big for long distance riding)  , 520 sprockets have 46T rear or 48T (take it from GD250R sprocket will fit)
If you keep 428 chains, try 15T front and 52T rear (Can’t change size on rear on 428 chain sadly) but if you don’t care about acceleration, 15T may help reduce the revs further for more speed
Don’t forget new clutch , new springs , and valve clearances go a long way , use the service manual (GV125 and GV250 are the same clearances as both engine use shims)
Grab a bottle of something like WYNNS FORMULA GOLD PETROL (search online) or similar (but do NOT get REDEX), just something like WYNNS Formula Gold Petrol in your country.
Pour the whole thing inside the tank (1 full bottle inside) , go for a ride until the fuel is low, you want this product to clean out your injectors, fuel lines, fuel pump (anything fuel related) that may have internal deposits / gunk and the pistons will burn it away.
See if the idle rpm improves.
– Check your tyres for cracks (very old rubber is dangerous)
– Disconnect your calipers from the brake discs, and clean your calipers inside with brake cleaner (don’t remove the brake hoses)
– Also check your pads, if the brake pads are thin, replace them.
– Check your sprockets for bad teeth or replace them
– The chain , if the chain is covered in rust or has tight spots in some places as you spin the wheel to check slack (put bike in paddock stand), replace the chain.Doing small things 1st above ^  before dealing with anything major.  If it is working normally, that is a good thing!
Oil = Motul 7100 is the best oil for these twins. It will thank you for it (or Silkolene Pro 4 oil)
Tutorial below
[How to Tutorial] How to Change Oil & Oil Filter on Hyosung GV125 GV250 GT GT250R GT125R
2500 KM is quite young!
AFAIK the workshop manual on oil presure check gives a higher number for 250 than 125: 250 -> 2.0 Âą 0.5 ă/ă (at 65 ââ3,000 rpm) 125 -> 0.9 ~1.1 ă/ă (at 65 ââ3,000 rpm) Unless itâs a typo maybe that suggests that oil pumps can be adjusted for increased oil presure?
Pressure is changed inside the engine because there is bigger holes for oil to flow around the pistons and cylinder head, also the 250cc has a bigger cooler, so need to move oil quicker as the 250 cylinders warms up quicker.  But i personally have taken apart both engines, the oil pumps look the same.  My suspicion is that the 250 will have a smaller internal sprocket for the 250 to spin the pump a little faster, but alas, i did not measure both oil pump sprockets.   The manual is correct that it makes more pressure, so i have been corrected there.
Both GT125R and GT250R have identical redline, it’s strange on GV Aquila as the redline is longer (doesn’t mean it’s good for it) , its the same engine used on both GT and GV.   Engine acts funny around 11,000 rpm (it doesn’t like it for too long) but peak power is at 10,000-10500 rpm.  Good cruising RPM is 6500-7000 rpm.   Higher good revs is 8,000 to 9,000 rpms  (you will feel it when you hit a certain RPM the engine has a better rhythm between 6500-8000 rpm, either 250 or 125cc) . Engine will last longer if you don’t redline it.
Download the service manual on this forum , and flick the kill switch red button 3-5x quick as soon as you turn on the key.
The manual mentions if you get sequence flashing red light, you must count them.
Eg. 10 flashes _ pause_5 flashes_ pause_6flashes = Code was 10-5-6 , the ECU will repeat itself to make sure you got it or if 2x parts have issues like a Lambda Sensor and Clutch Switch , then you will get 2 separate codes (example)
As the FI light comes on sometimes, it is also a good idea to strip down the bike and clean every connector you can find with contact cleaner
When you get to the ECU ==> Disconnect it and hide it far away for now,   then ONLY clean the ECU connector plug carefully with contact cleaner.
let the bike dry out its harness from the contact cleaner – don’t clean the ECU with any liquids.
If the ECU is dirty, only use compressed air to blow the pins clean.
Compressed air also helps blow a lot of gremlins in under the airbox trying to invade your plugs.
I say do this because it goes a long way to improve signals to the ECU, your bike may jerk due to signal loses (momentarily) which the ECU gets stuck on what to do next OR  you genuinely have a fault somewhere (usually means replacing the particular part if cleaning doesn’t solve it)
Download the service manual on this forum , and flick the kill switch red button 3-5x quick as soon as you turn on the key.
The manual mentions if you get sequence flashing red light, you must count them.
Eg. 10 flashes _ pause_5 flashes_ pause_6flashes  = Code was 10-5-6 , the ECU will repeat itself to make sure you got it or  if 2x parts have issues like a Lambda Sensor and Clutch Switch , then you will get 2 separate codes.
Its the best way , as the ECU will let you know why it won’t turn on the fuel pump until the errors are fixed.   Inspect the rest of the harness.
I have no good comment on those cut wires just yet, as it seems to come from the backseat, it is likely someone trying to trick the ECU in to “dealer mode” or it was part of some “aftermarket lights , cutting wires to fit etc”  , i am not sure, but i can’t see the full harness layout to avoid giving wrong answers. Seems other wires have been taped up in the background , i see bullet connectors that may mean indicators.
The service manual will have a wiring diagram that describes what should be at the back, as you’re looking at the bike yourself.   BLACK solid wire with a white line on the bike is always “Ground , negative , minus 12v from battery usually”  , all other colours point to specific things described in the manual in better detail.
There is a few on ebay that came out of a GT125 , the GT125 uses the same engine as GV125 Carb models. – You might want to message the sellers to see if there is any catch or work they need or if they are “drop in & ride away”
I wish i had one, I’m sold out on the 125 engines, but yes other sellers have it on ebay , fingers crossed for you!
Closed due to duplicate post. I have answered it on your other topic.
I used to use GHOST Drift cams and their little stick-on adhesive pads you an mount to the bike fairing if you want a bike view or helmet mount.
I heard GoPro must be better these days , i have not tried other brands personally, so its a matter of research maybe the top 5 camera companies used by Skiers or ATV riders, if these cams can survive harsh enviroments, they should be good for the street use.  The design / looks is of the beholder đ
I mean specific oil brand , some oil is cheap and doesn’t really help the motor but the service manual says if the bike is a daily rider or used heavily then use “Premium” oil.
I personally use Motul 7100 , i think it’s best oil for Hyosungs , compared to the likes of Castrol.   Another good Ester grade oil is Sikolene Pro 4 or Comp 4
A good oil can influence how slick your gearbox and clutch is , and how long it lasts before it “shears” off (getting useless around the bike)
10K on KBC bearings is my guess but i always changed them as in the past i had an annoying experience with the sprocket drum wobbling / grumbling before the bike hit 8,000 miles. When i switched to better ones, everything rolled smoother and had to be double sealed bearing rubber sides.  Never was a fan of bearings with metal shields on the sides.
These are my thoughts so far.  Hope they are useful!
Oil pump is the same but both engines make peak power at 10500. So anything above 11000 isnt good for the cam tensioners and valves long term but the 250 can tolerate it a little better than 125cc (just larger valves and pistons, crank, clutch basket , flywheel etc)
What exact oil are you running ? and do you have a picture or link for it ? also can you advise the last time the bike had its bearings changed out ?
Normally good bearings should have a double seal on each side of them (not metal seals) but the rubber seals built inside the actual bearing itself should keep it self-greased unless they are just due a replacement if the previous owner has put cheap ones in.
Pull the wheels out and look at the bearing codes, take a picture and go to any motorcycle shop locally and ask for replacement bearings for the wheels that match the codes you see on them, they should offer better rubber sealed ones (they will be self-greased inside) so you can swap and go.
GV250 EFi uses two cables at the bodies, so you may wish to talk to the seller that he may have sent a 650 cable by accident ? This below is the real GV250 cable i removed myself. https://www.ebay.co.uk/itm/257417684499
seller confirmed I have the right cable. It may be the case the Iâve routed it wrong. Iâll try again and add pictures of how I route it.
No problem but you must have two cables opening the front and rear cylinders then it becomes ONE at the throttle grip (2-in-to-1) style cable.
You got this!
GV250 EFi uses two cables at the bodies, so you may wish to talk to the seller that he may have sent a 650 cable by accident ?
This below is the real GV250 cable i removed myself.
It may sound crazy, but have you removed the throttle bodies completely and cleaned them out and replaced their o-rings , because if it is a sentec 2008, it will have been nearly 20 years of those o-rings cooking on engine head, microscopic leaks are possible cause uneven metering behavior for the ECU
Then also check your lambda sensor against the service manual values , it’s something i would check next , being a Sentec , it will be using an MS3-250 Hyosung lambda sensor if it has the old big white connector.
The check the resistance of the wire plug from the ISCV to the ECU plug, and see if there is a breakage in the harness , then find contact cleaner. Clean every socket you can find on the plug (every last one) , the ECU tends to get funny if one sensor is OK but resistance high due to oxidized or dirty contacts. Do not spray the ECU pins.  Wait for the harness to fully dry and retest ?
The worst case scenario is replacing the ECU if the internal chip has a fault (intermittent)Â – I am suspicious that a Sentec GT250 ECU will work on GV250 but I can’t promise this claim , so it is just my suspicion
There was a time years ago i saw ECU marked GV/GT250-Sentec  on sale. And it was factory made for both GT and GV (behaves the same as they used same parts in 2008)
Things changed a lot after 2009 which Daewoo and Delphi ECU’s
If it gets too crazy, you could switch to Delphi electronics which you can find easier on ebay but it means changing too many parts and you want to keep the cost low.
I pray the current ECU is OK and it is just a matter of harness checking , cleaning & throttle body O-Rings + lambda sensor checks
Info on the Sentec is limited as information is mostly disappearing from the web ,  it’s a good ECU if there is no issues , its just Daewoo was the worst ECU for the GV series.
GT125 uses the same engine as GV125 = Same motor but Hyosung put 87.5 & 90 on factory.
I am not sure why they put 82.5 , it seems too small!
You should do 87.5 front and 90 rear , like a GT125 = Then ride and report back.
Try fresh spark plugs (stock CR8E) , then look at their colours (plug chop to check lean vs rich condition) or show us pictures when you make a New Topic separate from this one.
If you are not sure on the slide needles , check this tutorial below
[How to Tutorial] Adjust Carb Slide Needle (Tuning) Hyosung GV250 GV125 GT GT125R GT250R
(GV Carbs have 5 groove or 3 groove needles , it just depends on model , but usually it is better to be 1 step richer , than normal so it helps the engine better especially in top gear so it does not lean out too soon)
