♠️ M77
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You are welcome 🙂 , i will mark this as [solved] , enjoy the rides!
`thsnks for your information , sorry not efi model . it’s a 2005 year.
No problem, a 1 man bleed kit should do it following what i said about the front potion where i sometimes do it the old fashioned strange way!
Ignore everything you hear about Hyosungs before 2020 online.
Unless they themselves have a GV300S , their opinion won’t matter, Hyosung has come a very long way from its 2001 early GV days. Because now it is an Euro 5+ bike, they have to take electronics even more seriously now.
Problems with GV300? = Not much , just take care of it, and it will keep going and it is Hyosung’s first 300cc liquid cooled motor ever. They did a good job.
The ONLY thing i would caution for reliability is NOT to use Lithium batteries (charging system designed for AGM battery) and upgrade to SHINGDEN Japan mosfet regulator. That’s the best electric upgrade for it. The OEM regulator is made in china , not in Korea anymore, so quality is hit & miss. I would put a japanese regulator there.
Ignition = Upgrade to NGK Japan caps because the stock caps can sometimes fail (it is made in china the OEM ones, it has plagued many motorcycles)
Coils = Uses Delphi Electronics, it is OK. 125 models were using carbs before 2018 and 300cc did not exist until 2019 , the EFi 125 sister joined in 2019
If you buy new, you still have a 5 year warranty , it is the first time Hyosung offered a 5 year warranty on a 125/300cc class machine in a long time.
300 would be a good balance to learn on it and keep it for a long time before you feel like upgrading to its GV650 sister. It is popular in europe now, there is also different GV300 versions , so choose the style that suits you (GV300R , GV300S, GV300X or GV250DRA-2025)
As you are learning on it, i would not worry about power, it will be there when you need it as you get more experienced. Chain Kits will be a future upgrade to change gearing (going faster etc)
I tend to fix a customer Hyosungs myself , it is always the older models before 2020 that need the most love and care but don’t worry too much on the GV300S , i can’t find much horrors of it yet (only stupid people blow up engines & blame the bike)
Tip = Use Motul 7100 oil every 1500 miles and use Motul Factory Line coolant and it will love you. (yes the Koreans do say in every manual that a commuter bike needs more oil changes than a seasonal rider, it helps it last longer)
Only downside i can think of is that it likes to eat brakes! – Expect to change pads often if its a commuter and it uses ABS so brakes will be engaged more , and it likes to eat clutch but fortunately we can throw away the stock chinese plates and use a beefier clutch kit (heavy duty plates) then its good to go.
Engine clearances = On the forum a member has done a guide about it already or your dealer will do it as part of warranty.
Tyres = They are OK in summer, winter can be sketchy but will be OK if you avoid ICE!, when budget allows get yourself Michelin or Bridgestone Tyres , I personally trust these two brands on my cold UK winters!
Just my random evening thoughts , hope that helps and go test ride it! – You might like it. 👍 – Hyosung has been around for a long time they made engine parts for Suzuki for years.
Excuse my grammar or spellings , i was typing fast before losing my train of thoughts!
You did not say if it is carb model or EFi, so my reply below will assume it is EFi model.
As it is CBS brakes, the rear cylinder being pumped also should help? Have you tried pumping the rear? – This is to make sure no air from the front has gone to the back or air at the back has gone to the front (vise versa)
A quick test = Disconnect rear cylinder or find a way to make sure the front caliper only has 1 hose attached to it going straight to the front cylinder , bleed & pump the brakes with a 1-man bleed kit found all over amazon / ebay. Keep doing it with the pads inside , so that all pistons push the pads together (don’t attach to brake disc)
Then disconnect it (dont push pistons) , connect the front and rear brakes together again (making sure the rear caliper has pistons pushed out to touch the pads without touching the disc.
Now Reservoir caps off from both cylinders for air to escape.
Push the pistons down flat inside the caliper (front) , you should see air bubbles in the cylinders making a sound or moving. Pump the front again until pistons full extend to touch the pads maximum, push the pistons back to flat, repeat this until you know the front is now good.
The rear should be getting better, push the rear pistons flat , and repeat, then test your brakes. It will be time consuming, but this is another “old school” method i use sometimes when i am doing multiple brakes at the same time or even my older generation GV that has two discs at the front!
Another way the bike loses pressure;
- Copper Washers on the banjo bolts need replacing.
- Pistons seals are hissing air or not sitting properly.
- Seals damaged for pistons.
- master cylinder is wanning. (if your pistons seized, your master cylinders where probably tired from fighting to push the pistons out?)
If it is a carb model = Don’t worry about rear (it uses drum brake) , just focus on the instructions i said about the front only.
Hey,
if you disconnect the RR itself, and do this:
– Rev the bike to 5,000 rpm maximum.
( I know the GV650 doesn’t have a Rev counter , so i assume you have a tach reader of some sort?)
(If not, try idle voltage + 1/4 throttle + 2/4 throttle) And Max throttle again (although hyosung does have a hard limit on their manuals for the AC output at 5K RPM mark, if it exceeds that , then further revs don’t matter as its replacement time)– Connect the meter to 500V AC and probe any of the 2 pins of the 3phase yellow wires in any order and do it 3 times.
Eg. Pin 1 /Pin 2 = Voltage?
Pin 2 / Pin 3 = Voltage?
Pin 1 / Pin = Voltage?Then let it cool down for least 12 hours outside in a shade (away from any sun heat radiation) , or overnight is best.
Get the meter out again switch to 10 OHMS (Ten) and probe those 3 pins again. And report what each combination says 3x
Resistance is the pretext to fry electronics (slow cooking) therefore the harness weakens. Hyosung has used thinner gauge wires on the EFi models compared to carb models. And also any oxidization of the pins , increases the resistance of the plugs connecting the stator to RR to harness.
Furthermore, is the stator OEM or aftermarket ? and I assume it is still using DAEWOO ECU? (We got Delphi in 2012 here in UK but also Daewoo units phased out by 2014) – It is the Daewoo Electronics that have plagued the 650 models and 250cc models but fortunately we can fix certain aspects of it.
Normally I put an extra red wire from the RR to the battery with a 10A fuse. I’d rather a 10A fuse blows up so i know it won’t cook the battery next and the RR is also still connected to the main harness which either uses a 20A relay box or 15A fuse or 20-30A fuses (Hyosung made variations of EFi harness over the years, so small things change)
Before I digress further, I will await the report of the stator information, it is best we start there. The RR can’t do anything until the stator feeds it.
i will assume you’re not using a Lithium battery (if so, I would advise against it due to the variable voltage nature of the Hyosung charging system which Hyosung manuals state it can tolerate up to 15V but 13.5V minimum DC to start charging the bike)
Keep in mind, if the fuel pump is OEM and suspicious or some aftermarket version, it may contribute to the additional charging system taxation which the RR will just get hot. Daewoo pumps are specific as they run different pressure ratings compared to later Delphi units. Daewoo pumps are Black with OEM numbers printed on it (the Aliexpress clones are black/blue intended to run the Delphi systems – Daewoo stopped making their pumps as they went out of business. So fi you find another used Daewoo pump , look after it.
I can’t remember if it is 3.5BAR or 3.0 bar but it is possible to manually check the pressure yourself.
Something else came to my mind but worth thinking about, in the context of the charging system, this “extra” resistance (aforementioned above^) does not necessarily mean the regulator will “cook” due to higher current; rather, it indicates a failure in the efficiency and thermal integrity of the stator itself. henceforward we must address the stator first. The general consensus amongst 70% of Hyo 650 owners who keep their bikes longer than 5 years (not the stupid 1 summer riders who switch bikes after abusing it with cheap china RR’s and fitting lithium batteries or crashing them because they are too throttle happy on the streets as their race track are ones you should not seek advice from) is to make sure the Stator is in good spec all the way through , connectors are not oxidized (common for brown burns to to happen there) and fit MOSFET RR’s but beware there is a LOT of fake mosfet RRs and even the fakes are now becoming almost hard to detect , real Shingdens (mosfet kings) are very expensive brand new. A used one from a local bike you can see running with your own eyes is better salvage but still costly. OEM RR’s have always let me down as Hyosung doesn’t make them , so its an outsourced product.
Also where i mentioned checking OHMS of the stator cold (about same temps you would check valve clearances) , this springs to mind , If one phase is example 3OHMS and others are different like 2OHMS (Pin 1+2 = 3Ohms , Pin2+3=2Ohms , Pin1+3=2Ohms), the RR must handle an unbalanced load. the OEM RR uses either SHUNT or older diode tech (depends what Hyosung gets as they have many variations of their RR’s being made, it’s hard to keep up) , which dumps excess current “somewhere” to regulate voltage. That kind of imbalance could cause uneven heating of the SCR, or diodes within the regulator, leading to premature failure as you said that as soon as you run the bike , it is not long before it’s “cooked?” . Just my random suspicions but please investigate and correct me if i am wrong as i am hoping we don’t have bigger issues on the bike and it could just be something small that was overlooked!
Can you show us a picture of this part ? Upload it here. Just to make sure Hyosung hasn’t updated the spring design (caliper stays the same) but spring (anti rattle might change as they outsource these things to other companies making it)
I dont have those at hand as its not something i keep on file, but hopefully someone else does. Though, try to look for a crashed 250cc and ask the seller for the ISC unit, so you can double check but also clean your contacts (every plug on the bike including the ECU socket) incase of oxidized pins affecting ohm readings or water ingress found ?
Just an idea!
Tak ale pomiaru dokonałem na zdemontowanej panewce co przekłamało pomiar
The forum doesn’t auto translate sadly , you would have to repeat what you said in English, sorry about this!
it could be possible you have sticky slides that wont go above a certain RPM
Have you tried this mod below?
[How to Tutorial] Adjust Carb Slide Needle (Tuning) Hyosung GV250 GV125 GT GT125R GT250R
Least you want to investigate the needles are also not getting jammed inside the Needle_JET tube (brass) , as the more revs you need, the higher the slide must lift for air passage and fuel to leave the main jets.
Not unless the the skeleton of the carb itself , needs compressed air (again yes)
This is the closest video that explains what part of the carb is activated and gives you more pointers to look for
(Video is only viewable on youtube, due to the uploader making it that way)
have you measured your old parts first ? it would be easier.
Nice work Nigel , who would have thought! – Another reason why we sell appropriate sized filters for the GV125 fuel line kits with a good flow rate.
Keep an eye on her and take good care of it, we’re right on the riding season , I can’t wait to take my babies out, after a LONG depressing grey UK winter lol
I hate to be the legend that upsets you but slowly , investigate the stator (drain oil first) – I believe it would be a good idea to get a new good stator.
Also replace that regulator. never trust a regulator that is not a real japan mosfet shingden on EFI bikes because there is too many sensors that depend on a very stable voltage.
Stator = I had a 3 customer bikes in the last few years where stators where the reason bikes did not cold start properly and i had to replace everything else on the bike, i did not realize the stator was fault.
Bike 1 & Bike 2 = Wrong stator fitted.
Bike 3 = Pulse sensor went haywire.A carb model will get away with a bad stator and bad regulator for a while (in limp mode) as it’s just only worried about a CDI unit.
So yeah, lets go to the stator and regulator unit. Keep your old one for purely emergencies but i doubt you will even need to worry about it as a true mosfet shingden regulator will last years and years and years , I still have the same one my bigger GV EFi model. Everyone knows getting a Daewoo ECU for the GV650/GV250 is like going to war! No gold to be found for 99% of the earth. The regulator was needed to be upgraded even with an inline fuse to avoid electrical spikes to it.
Bike wont start without a stator anyways , it’s the 1st object the bike looks for before triggering anything else. If it starts when warm , but refuses after its cold , check how much battery has drained (if 12.9V in the morning , then check overnight how much voltage was lost)
Get your mechanic to do a “LOAD” test on the battery too using a special Yuasa Analyzer (usually mechanics or garages keep this)
& yes , Hyosungs have a character of their own! Must be a Korean thing!
Does it spark well when its ice cold for hours ? Check your coils if possible ?
To start the bike we need 3 things = Stator Signal (crank spinning) , Injectors firing and ignition coils firing the plugs nice and bright
I would be suspicious of the stator ? It is easy to put the wrong one too or that the pulse sensor seems to hate the cold (ECU thinks dead signal recieved = cut sparks)
Your wobbling = Find out what cable wires are moving and check them (eg ? Clutch Switch sensor, KillSwitch Plug under air box could be covered in crud/dirt ?)
Roger, topic closed.
Continuing the conversation here
From your google drive image , 2_1 , 2_1 ,2_1 in that sequence is = Intake air temperature sensor
This is the sensor on the airbox itself. To diagnose this, go back to the service manual and search “C21” code, there is a diagram they wrote on how to test this.
Also it would be very wise to get compressed air (air only!) and blow every connector on the bike clean, so you have to find a day where you strip the bike down and take your time, remember where everything was or label the plugs if you want.
No liquid cleaners on the ECU sockets whatsoever, that is the most sensitive and most infamous ECU that plagued the early Daewoo GV250 models, so much that Hyosung moved on and switched to the Delphi Electronics.
So look after that ECU like your life depends on it and if you have to , buy a few fork gaiters , yes fork gaiters , and use them to hide plugs away from exposures of the road / rain / salt etc..
Use a “tiny” drop of contact cleaner on every plug you find EXCEPT the ECU plug! – Leave to dry overnight.
Get a can of “ACF50” , apply this in every plug you can find , EXCEPT the ECU plug again. (This is oxidization protection / anti rust measure)
Hopefully we get some progress ? keep us posted!
Check this out, there is an actual pin out for the 3 plug CDI unit
Needing a little help with my current project (+GT125 CDI PIN OUT)
See if that lines up with your bike, otherwise as you said, if it runs , i would not touch the CDI again haha.
Get a fresh set of CR8E from halfords , those plugs. Do not use “IX Blue Box” iridium plugs as Hyosungs are not keen on them (Hence we use stock ones or LASER type plugs) but i am digressing.
Go for a short ride with new plugs. Come back. Take many pictures. Upload them to this forum so we can see , if its electrical issues we will tell. Also label with plug is front or rear.
If not, upload pictures to GoogleDrive/OneDrive and make a “public” folder called “hyoforums” or something else , paste the share link here , whichever way is easier for you.
I hope also the throttle slides (diaphragms) have not got sticky , if they did, they will cap the speed the bike rolls at . They need to lift fully and smoothly to allow more fuel . the faster you go.
As long as it has the original AirBox on it, the K&N catridge + updated mains should be fine. Main Jets only activate fully when on the road.
If in the garage / stand still traffic, its your pilot jets that do the work. See what happens when you do a deeper dive over the weekend.
Good luck!
Hmmm, try ebay UK or ebay EU for “GV125” CDI as they use 6 pins but if possible at all , can i ask why the need to replace the CDI if the bike is working as it is ?
Also, upload a current picture of your CDI so we can see the underside of it, then i may see if other Hyosungs fit that you may scour a used one for cheaper ?
Regards
