♠️ M77
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14 down from 16 would throw timings off yes and likely as Simon was saying that you may have hit something inside the engine, as there is a very small margin between the piston and the valves.
Like he also said, put some petrol or some liquid through the valves and see if they leak through without you pressing them down, it could be better than just visually looking at them. I would mention a likely hood of needing to replace the valve seals (if i didn’t say it before)
Rebuilding the front engine is a good idea to put fresh life in to the bike again.
As the engine cranks , the ECU should be enriching the injectors so it fires up quickly then the ISCV takes over to idle the machine.
So when turning on the key does the fuel pump prime (any noises?) and if you cranked , does it spark ?
if you’re sure the harness is spotless , we could check the Clutch Switch , Neutral Switch and Stand Switch, these definitely also cut the injector and sparks off.
If not, keep an eye out for a backup ECU you could get
Go for a small ride and come back, let it cool down quickly , report back on how it ran on the road ? And then remove your plugs , check again.
NGK is a safe call for caps. And test the resistance of coils and report back the figures.
Check the manual and test your Lambda Sensor (O2 sensor) in the exhaust pipe too. These report back burnt (or unburnt) mixture back to the ECU. Sometimes they just crap out needing a replacement.
Although, the only way to be sure about any part is to use the manual and actually write down the figures reported , then you know if a cerrtain part needs replacing. It could take 1 random sensor or part to throw whole bike out of balance.
Thermostat jammed probably , it should open and allow the radiator to get hot , there is a sensor in the bike called WTS (Water Temp Sensor) , sometimes that could also be the culprit.
Also , there is also another sensor called Fan Switch (That triggers the fan to turn on)
Fortunately, we have the service manuals in the forum which locate where they are and how to test them 🙂
Good to hear its alive and kicking!
13.5-14.5v yes to the regulator. If it gets hot just being there, i mean hot, replace it right away.
Could be pistons/piston rings or valve seats themselves as long as you are certain the valves are 100% straight.
Put a new metal gasket again just incase. (Compression loss due to head-gasket failure can happen , just like cars)
The site’s image uploader seems to have bugs i am sorting soon, so in the interim, use this website to upload images below:
https://postimg.ccThen just copy & paste forum links that start with
"[ I M G ...........]", this forum will translate them in to live images.Sorry for the hopping around , I will fix the site’s uploader.
I will fix it again don’t worry, bugs seem to crawl back again!
Least the postimage site works totally fine (not blocked by the UK yet & I hope not – stupid laws!)
The headlight looks good on your bike, i see the angel eyes ring lights are getting trendy these days 🙂
No IAT on the GV250 is on the airbox and ET on the physical front engine cylinder.
IAT = Ohms text.
ET= Ohms test.Don’t put IAT in water.
If there is continued issues with the ECU, there is a new upgrade system below: (I sell the fuel pump separate if needed) , i “may” still have older sensors like ET etc… I can always dig them out and see and included them in the bundle.
I have fuel pipes for the GV , eBay does not allow me to export them. So best to do the deal via email instead , or otherwise look for Delphi systems at your local wreckers , now you bike has a 2018 overhaul and yes I also sell the 2018 stator & regulator as they are entirely different now.
Harness & ECU = https://www.ebay.co.uk/itm/257182139648
2018 plugs for injectors & ET sensor etc = https://www.ebay.co.uk/itm/257148903272
Fuel pump wire = https://www.ebay.co.uk/itm/256602588520
Fuel Pump (Delphi ECU uses Blue Pump and has different pessure rating) https://www.ebay.co.uk/itm/257147094683
Main fuel hose = https://www.ebay.co.uk/itm/257155594594
Injectors = Hoses are OK , but i would get braided ones (can be supplied if needed) https://www.ebay.co.uk/itm/257150820566
IAT Sensor (untested) = https://www.ebay.co.uk/itm/257147129279
ET Sensor (untested but i am suspicious it works) = https://www.ebay.co.uk/itm/257134793489 (for future spare!)
TPS = https://www.ebay.co.uk/itm/257150787245
MAF = https://www.ebay.co.uk/itm/257150806030
IAC = https://www.ebay.co.uk/itm/257152400938
Stator/Reg combo = Needed for 2018 harness! = https://www.ebay.co.uk/itm/257148968953
There is a few variations of 300S as Hyosung is updating the look of the GV300S faster than we can keep up, there is now 300-SS , 300SA , 300R , i don’t think they will continue to make the early S model for much longer as they progressively move on from it.
2018-2021 (pre-facelift era) would be your safe bet for looks wise (plastics) if hyosung changes plastics, the frames would get updated with new mounting points which makes it harder to fit on to older models without modifications etc.
300S is more wide spread in asia that’s why and EU/UK is a larger 125 market, there are some german shops doing things like backrests, saddle mounts, even SHAD EU does nice hard tail boxes for them.
Exhausts = Look below:
What other parts need attention on the GD250 ? We could elaborate what ever the manual isn’t making sense of.
Manual is OK for most parts as GD/GDR share the same parts under the plastics.
GD250N / GD250R = Plastics and extra fairings and race-look.
Tank is the same and so is the pump, however they are expensive to replace and easy to break the pump connector, so lift very very slowly and unclip the high pressure hose carefully and then tank can be put away to the side , keep in mind there is likely the ECU attached to the tank or regulator. Hyosung has moved parts around the GD250 & GD250R frame under the tank to try cool down either the ECU or Regulator.
I had a different bike in the past that had its ECU mounted under the tank (on the tank itself) and i almost yanked it off! – I learned to be slow in everything now.
Thanks mate Not after more power and also not expecting any, just like the look of it 😉 Barry
Further studies and testing on my part will be conducted when I can, as i would like to make some mods for those newer models too.
Power on a 125 is something i will work on! – While the EBC clutch upgrade is good (on the shop) better than stock, I will be trying a carbon plate (yes real carbon from EBC UK) , only 1 rider said it is a little improved over EBC HD , he is still testing…
Looks = Beauty is of the beholder haha. (my eyes prefer the older S look as i loved the older GV models, so a bobber isn’t too bad) , new model USD forks make me worried about chrome rot or stone attacks from road , RWU forks are easier to maintain than USD forks.
They did the same thing with pre-2017 GV125 and GV250 = Same chassis , same air filter , same coils, but as GV250 got more improved over the years , less parts started to fit GV125 Carb Model (because after 2008-2010 GV250 started to use EFi parts, and we could not even use EFi parts on the GV125 carb model)
Eg. GV250DR / GV250DRA = Air filter does not fit at all , it looks the same but they forced it to only fit 2018+ model and only Hyosung makes it.
GV125S/GV300S were identical in 2019-2021 (for plastics and fuel tank) , but as you found out now, due to newer Euro5+ laws passed in the EU, hyosung is doing GV125R . GV125X , GV125-SS EVO (USD forks) , they started to change little parts inside there and there even engines have newer casings. Injectors in GV300S will not even work on GV125-S , etc …. It starts to get complicated , as you go deeper.
So if you wanted to use a GV300S part, it is safer to go for 2018-2020 models before the 2021/2022 facelift. GV300-SS (GV300SA) definitely has a different style airbox and i can’t confirm yet it fits GV125-S due to throttle bodies ( i need to buy a GV300-SS throttle body to verify this )
They are changing GV125-S / GV300-S too fast for me to keep up lol.
However, don’t expect any power improvements using GV300S air filters, blame the stupid emissions laws in EU
This is the recent facelift 300S (SS / EVO ) – There is also an R model in Israel, looks same as GV125-R in France (Sima Moto is the main EU importer)
IAT = Air intake temperature sensor (for airbox) checks the air inside and reports back to ECU
ET = Engine Temp Sensor , it is on the Front Cylinder Header under the metal manifold.
Service manual would usually tell you where these things are and how to test them properly , the IAT would just need to know OMHS readings not voltage.
(Heat changes the resistance = so ECU would know if the resistance goes up , it means air is less dense as more heat reduces oxygen density)
So i would definitely follow the manual checking sensors 1 by 1 first. Some sensors only need ohms readings. If you applied voltage to them, it fries them and you will need to replace them again.
Cold starts where not an issue, and sometimes when its hot, it dies, then i have to continuously crank to get it going which damaged the starter motor in the end , so replaced the starter motor too and its relay.
You could check the service manual for the EFi models to check resistance levels needed for the coils and make sure your coils match (I can’t confirm what the SV650 ones are as i forgot!)
However Hyosung GV650 carby , GT650 carby & GT250 (some efi early models) did use the Mitsubishi Japan SV650 coils (It will have the Mitsubishi logo imprinted on it)
Some GV25o EFi models used GV650 smaller coils – So Hyosung has been known to interchange coils across all their models as long the specific ECU accepts it.
Speaking of temperature, test your ET sensor , here is a similar topic about it:
If the bike had brand new parts (or used parts from a verified working donor) – you should not have problems. This means now, you will spend some time with your multi-meter to test every single sensor on the bike and verify that it is still spec according to the manual.
Probably not (not 100% sure yet) , as GV300 has 3 different designs now (GV300S, GV300SS, GV300R etc…) and I am currently suspicious that the GV300S may be using larger bore throttle bodies (I haven’t personally taken apart both a GV125-S and GV300-S in my workshop yet , there is more 125s in the UK than there is 300s)
I know 100% that Hyosung is using a newer design air filter now going forward, it is like a flat pancake style filter now.
Why do you ask ?
IMGUR is now officially blocked in the UK 🙁
Is it possible to upload on this site directly (you should be able to see the “add media green/blue button” , if not , let me know and use a site that’s called
https://postimg.ccGlad to hear the GD Exiv is doing well 🙂
Check your coils for resistance and see if your HT Caps are arc-ing (loose sparks out of the plug)
This says its for 125GT but ignore the title, you want to use it as a guide to check resistance of your coils and the stator unit too.
Rectifier – How to Test Stator , Battery , Regulator – GT125R Carby
I once had to replace everything on a 2012 DAEWOO model GV250 and the customer was also stumped, it turned out, despite the stator working, it was the root cause.
How? The resistance was OK for the pulse sensor and stator was charging 70v strong around 4k revs , but as engine got hotter and hotter, it started to die down.
We replaced the stator unit , and it was fine since thenAlso the Daewoo ECU is my most frustrating ECU to work on compared to Delphi or Sentec ones , they absolutely want every single connector on the plug to be free of rust , oxidization, dirt etc. Contact Cleaner is advised.
Do not put liquids on the ECU itself = Use compressed air only. Just the ECU area you have to be extra caution, it only takes 1 wire or 1 pin to ruin the whole thing for good and it is near impossible to get a new Daewoo ECU.
I would deal with the TPS later, as its already idling at 1.5k rpm, although just a minor tweak should make her idle at 1800 rpm (Brand new GV’s idle at 1800rpm straight from the factory, it was the carb models that idle’d lower around 1.5K rpm as mandated by the Hyosung service manual)
Also it helps to get fresh plugs again (CR8E Yellow or LASER Rainbow plugs only) – They don’t like “IX Iridium” plugs.
Also if it has stock plug caps, throw them away, they always let us down , and get yourself NGK caps. Very recommended.
If not , use SV650 1999 caps (ensure your engine hole can still be covered to stop dirt or water going to your plugs!) and use SV650 1999 coils (they are bigger) but made by Mitsubish Japan (get OEM ones) , they may be big, so expect to make room inside your plastic cover under the tank for them.
However, if your HANKUK Korea coils are OK, leave them there and just focus on the HT caps. Generally when the plugs and caps go bad , it takes out the coil with it!
Check this out too:
The ECU needs the temp sensor working, it helps it regulate how much fuel goes in there, if cylinder is hot , it tells ECU send more fuel to stop it going lean condition, and it controls your IAC (idle control valve stepper) when the bike is at idle too. It is not good to bypass it. Hyosung has used a small margin in their ECU map code , it means it can’t compensate too much or it shuts down to protect engine.
So i can’t advise a Bypass but , find in the service manual the highest resistance it takes and max temps (eg. 4,000 ohms at 100*C degrees ) and try to find a similar sensor that has the same readings at 25c, 50c , 75 , 100 etc, if it matches the service manual , then use it. Get your mechanic to match the thread on the engine , eg. OEM sensor takes 11mm threads and uses 1.5 pitch , then get a sensor that matches that.
Otherwise, hunt a damaged Hyosung in your country (crashed bike) , and get its ET sensor from them.
I have not yet found a replacement sensor that uses the tiny connector Hyosung uses. Most sensors for bikes and carbs use big plugs , so Hyosung made it difficult.
I would not cut your wires.
If you find a sensor with a different connector (as long as it matches OEM Ohms & Temps) ==> Get a spare “injector + ET” harness from any 250cc EFI hyosung in your country (GV250 / GT250)
GV650/GD250 use water sensors, so they will not work without making the job extra difficult retrofitting it. Some people tried to put a WTS (Water Temp Sensor) in to 250cc Oil Cooled ET port, they almost damaged the engine, so it is risky and almost not worth it.
GT uses more vacuum hoses due to it having a vacuum petcock, but GV has a manual petcock, only worry about Front & Rear engines sending air to the fuel pump. That’s all you need to worry about.
Now, the other pipes like EGR (if present on the bike,) throw them away, the bike wont miss it , infact it will be glad as those things are parasitic (robs vacuum energy) and block the metal tiny pipes at the engine side and then block the airbox’s extra ports.
(I would doubt it , if it is a genuine 2000 engine it wont have egr ports , thats something added to later 2005+ engines to meat the silly Euro3 laws)
(UK for now doesn’t care so to speak as MOT testers don’t check emissions on carb 125 bikes. Just exhaust loudness that’s all.)More on that here:
How to change Vacuum Lines on Hyosung GT125R GT250R & GT Comet (Air Hose Diagram)
For fuel (liquids) , here is a specific tutorial , follow it exactly.
How to change / upgrade fuel lines & fuel filter on CARBY GV125 & GV250 Diagram
The Carb Float BOWLS = Have extra hoses on them that are basically overflow & drain ==== guide them down towards the road. (if you have V1 carbs)
If you have v2 carbs their overfow & drain pipes will be both on top of carb and bottom of carb ==> guide them down to the road.
If still stuck , post some pictures so we can where you get stuck.
Good luck!
Red and Orange will turn the bike on.
Others are not that important but the ignition lockset will have 4 wires coming out of it, just incase the black/white + red/black wire is needed by the harness (ie. other auxilary parts being turned on. )Test with Orange and Black first and test the bike.
If in doubt or it’s not working, post some pictures here.
thanks for the replies. I will look into those after this. I forgot to mention that the FI light is also on. then I turn on off key 3 times, FI light blinking x10 x1 x1 x8, which I think the error code is 0118. I found out online that error code 0118 is related to WTS (I assume it is same as ETS= engine temperature sensor) Is this also possible cause to my bike problem?
If the ET is fautly , the ECU won’t know how to keep optimal fueling as the heat rises , so it has to sense it. However fortunately, you can always remove the ET , get 2 bowls. Cold water and 50% hot boiled water. Get a mercury thermometer in there to get glass readings
If the cold water says 7C degrees , put the sensor inside , get someone with a meter to help you. your hands hold the sensor down to the water but do not allow the “black part” to touch water as it will corrode the pins!
The 2nd person will get a meter out and switch to 100 ohms ===> sensor says 25.5ohms and manual says around 0-10c sensor should be about 30 ohms . Repeat the same process for the hot bowl. These numbers are not true , I am just guessing, the 250cc service manual will tell you the real numbers to look for.
This way you can verify if the sensor is working according to different temperature or if it is behaving faulty (skippy , jumping numbers etc….) , then yes replace the sensor.
It is also very important to make sure the tiny connector is clean and its plug, if there is a bit of rust / oxidization, it means ECU gets less optimal feedback or zero feedback as the current is not enough for the ECU to sense it.
Just like fuel tank, if the float is at the bottom it could say zero ohms ==> dash board says hey your fuel is empty , and a full tank will have a high float, the fuel sensor will report 250 ohms , dash will say you have full = bars of fuel.
Ohms are very important readings for the ECU for sensor like Temp, Fuel , Coils (Stator) , etc
