♠️ M77
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12 Bar is very good, that is like 175 PSI for a 125cc Hyosung twin. So engine is OK.
For the engine, now if the top speed is poor, i would definitely check with service manual these 2 because it is also true;
- Valve Clearances
Get a feeler gauge and follow instructions and see if any valve is out of spec?
Tight valves = hard starting / overheating / poor speed.
Loose valves = noisy / poor speed / dangerous if too loose, it will annoy the chain tensioner. - Clutch Plates
Get Venier Calipers and measure clutch springs and measure plate thickness vs manual oem limits.
Bad clutch = bad speeds.
Beautiful big (heavy!) girls the Korean bikes are but they like to eat clutch and brakes!
So if engine is sorted, next step try these tips:
– Show us which caps did you get ? If they are NGK CAPS, then no problem, ignore this message.
– Next tip, replace ignition coils. (Better ones , like these we have )
Do not buy rubbish chinese knock offs.
If you do not want to wait for us to ship coils, then you can go to your local junk yard (scrap yard) and find SUZUKI SV650 1999 (1999 only!) good condition working coils and try them.
They are BIG, so they may cause issues fitting it!
Hyosung GT650 (2003 iirc) and SV650 use same coils because they are japanese and made by Mitsubishi. These are the “only” korean coils we don’t mind keeping haha. After 2003-2005 iirc , Hyosung used different coils
Fuel System next,
– check air filter is new and clean ? If i have already send you new air filter, then ignore this
– Carb cleaning by ultrasonic will help.
– Did you replace manifold ORINGS rubbers ? (intake pipe o-rings) ? Maybe i have already send you new ones ?Hello!
Welcome to the website, it is good to see you here 🙂 , we have other riders from Japan too , this guy below is a regular customer of mine and he rides a GV125 too, this is his profile.
https://hyoriders.club/members/eisukesaito/profile/If you see other riders in Japan, maybe you can share this website to them too 🙂
I like your bikes, the Side-Car (we call them in UK) , is quite a rare thing to see on our roads, that’s amazing! Nice work!
You are welcome to share more pictures here ;Hey,
I am very happy for you that the bike finally ran, i did think the CDI was sort of the last resort item for sparking woes, now if anyone has similar woes, i will make sure to make them digest this topic. Very informative! Hell, you even laid out you tested some electrical components and what the specs are.
Usually some folk can’t or won’t want to read the manuals if it is too confusing for them , but not always!
I’m quite jealous you won a cheap auction backup bike but that will come in handy as parts donor for your racing days, you won’t have to wait to replace anything or just have an extra girl ready to go! A little switcheroo won’t hurt haha.
As for the harness, if the ignition system has to pulse 10,000v to spark the plugs, i would not be surprised if the koreans added one way diodes or some other mystery sensors embedded in the harness so that things don’t retrograde back if something doesn’t go to plan.
The horn does draw some power to be fair and it’s always live (as long as engine is running) , so all the rider does is press the horn button to complete the circuit. You don’t have to be a full electrician right now to know sometimes bad coils will arc the sparks or zap signals out of their HT leads , the harness must not get fried back or the cdi. It isn’t fool proof since the stator unit can still blow the cdi or blow ignition system system.
Just make sure it produces 70v around 5k revs and never exceeds 90v in any revs , it is almost the hottest thing on the left side of the lower crank.
When starting the bike -> magneto tells cdi how fast the rotor is spinning -> the CDI then tells the dash board (rpm signal bouncing around 600 rpm) , now the cdi next has to communicate with the rest of the ignition system to spark the plugs (as long the clutch switch & kick stand doesn’t prevent the CDI from doing so – – ie. safety cut out — (ie to avoid setting off with the stand down or starting the bike without holding clutch)
Neutral sensor isn’t foolproof , it may say N but gearbox may still be “slightly engaged” , alas when bike starts , it rolls 3 seconds later and falls , oh yes , i’ve witnessed it haha. I always make sure to roll the bike forward and back anyways to make sure its really neutral , keep gear linkages greased up and sparing no expensive on quality oils. That will keep the valve train silky smooth (oh yeah, the engine doesn’t have a camshaft under the gearbox too)
I’m a bit sad you’re leaving haha, i though the bike would stay married to you even if as a winter hack ?
Keep the big toys in hibernation till next summer even.
Perharps a GV650 will tempt you ? haha
The 2 black spade connectors going towards the oil cooler is for the horn system.
I know even the 650 has a wiring diagram that says “igniter” on it and it is usually a strange mystery object or plainly exposed , however korea makes the harness.
Otherwise if there isn’t some sort of mystery sensor for the coil at the front section only , then i will suspect the harness itself allow the CDI to deal with igniting the coils directly without some sort of diode assist / or igniters.
Since fitting new coils …. These would also cut sparks off (and i will also assume they have been checked already ?)
– > Clutch Handlebar switch (bypass it, because it’s a race bike, you won’t need it unless your local club says it must be present)
– > Kick Stand switch (bypass it)
– > PickUp Sensor from the Stator (but it works as its circuit isnt dead and is in good ohms spec)
– > CDI unit.
-> Regulator Unit (You can contact some local wreckers and ask for a Kawasaki Mule regulator and a genuine Yamaha r1 regulator. Please avoid knockoffs because it’s not fun to see regs in smoke – its so common usually electrical issues we tend to only blame the coils, reg and stators because Hyosung doesn’t make them , but they are outsourced parts to some other korean company to do it. I digress, sorry.Here is another hint, if you have a Digital Dash connected to the harness, you will see the rpm counter bounce when its cranking – That confirms it magneto is spinning 600 rpm as the typical speed of the stator motor to crank a heavy 250 flywheel.
I know you said the harness is checked from end to end with a meter, every wire colour you can find matching, so that’s great. I “should” assume the harness is okay , i can’t see it being fried from the pics or toasted up.
Perharps a spare harness from the wreckers and swap over the diode sensors and try again also ?
Keep us posted please. This is interesting.
Yes, Hyuindai Electric Red 🙂
Credits to a member from facebook, so i’ve remembered it ever since. I know because my bike is red and i like colour to match exactly.Just gotta figure out the exact Korean car that has diamond sparkle white , if anyone ever knows , share it away!
It could be advised to replace the front ignition or both of them (and keep one as backup).
Also when bike is running this is OEM values for charging system on your battery
- Idle 1800 rpm hot = 14v
- 5,000 revs = 14.8V (15v max)
Regulator that’s producing 13.x or 12.x volts in any revs is not good. And to be honest , a lot of owners worldwide replace regulators for better ones because the Korea ones are not great. Hyosung does not make them but they ask another Korea company to make stators and regulators for them. But i digress sorry , have a good session testing it and let us know.
Also, maybe get a USPRO Compression Tester from Amazon and check your compression for your pistons , after the engine is about 20 mins hot.
Sorry for the delayed reply. You got this 🙂
As per photos , you are correct 🙂 Diodes / Mystery Sensors and the black ball thing is likely the “igniter” which is part of the sparking system too.
They have wrapped that so tight with only black wires out of it suggesting its not something that fails often , i hope not.
Post a picture of your situation of the fuel sender, so i see how water is invading it or how bad the oring is .
Regards
Hello,
If you are checking for sparks, you should also rest the spark plug on the the cylinder head bolt (or any part of the frame that is not painted) so that you get a good ground connection. Then see if the sparks are strong or poor when cranking the bike.If you suspect the sparks are coming out of the cables when engine is in idle , you should replace the coil and HT cap.
Did you also do other checks i said above ^ ?
Yay!
Glad it’s all quickly sorted out, if simon says they are cool , i guess they are an alternative source otherwise i was about to refer you to TNorthEast or Startrights Leeds , incase i don’t have the cables you ask. I tend to keep some old ones for the ebay store.We all know not to order anything from hyospares or (scam-spares more politely!) by now and its clones.
Keep us posted and ride steady now.ah ok, I’m from Leeds originally so know start rights well. I’ll pop in next time I’m back home. thanks.
Tell them Marcel sent you, and you may speak to the actual boss to help you faster if its urgent. I know he does daily post runs .
Best of luck with the coils, i do also have a suspicion that the harness should be in the list of investigation as per my previous comments. Neutral sensor works if it says “green” on the dash.
Mind you the harness itself has mystery sensors embedded in them (hyosung calls them diodes) and there is a strange ball diode near the front call , we call that the “igniter” , to do with the overal bike sparking system, so have something “MANNOL TAPE” to retape the whole harness properly if you ever check the diodes are okay. Your meter will probably have a DIODE test function on it for the mystery sensors embedded in the harness. Hyosung hasn’t told any one how to test them , other than replacing it or replace harness.
The flat rectangular sensor that’s near rear coil section also is Neutral and rear coil. Just a heads up.
Hey,
Have you had a chance to test the stator ? Since no sparks will happen if this unit is dead. Check the resistance of the coils (3 yellow plug) and also critically the “pickup sensor”
if possible, also post a picture of the stator and your flywheel and i will confirm if they match each other.
Also while at it, under 1000 ohms or 100 ohms, test each single wire from the CDI plug to the relevant wire colour that corresponds it to rest of harness.
Ie. Blue = stator , green = stator , black with yellow line = front ignition coil, blue with white line, rear ignition coil , that’s just at the top of my head 🙂
- Side Stand Switch (bypass it) (bridge wires and protect it from rain with tape) be OCD about since hyos really hate it when water gets to the electronics
- Clutch Lever Switch (see this item here ) – don’t try to bypass it. It is there for good reason for the benefit of the gearbox too.
- Stator Magneto – > Check resistance of the pulse sensor with a meter under 200 ohms and tell us what it says
(Blue & Green Plug from the stator)
(Bike stays OFF, keys Out of ignition) - Stator Magneto -> Do the same with the 3 yellow wire plug (Pin 1 & Pin 2 = Ohms? , Pin 2 and 3 = ohms ? Pin 1 + 3 = ohms ?)
(What is it under 200 ohms? Tell us. 3 tests ^ above , 3 results . eg. 1.2 , 1.4 , 1.3 ohms = each yellow wire has its own ohm reading. it’s called a 3-Phase stator)Dead stator = No sparks will happen. So this is important to check. - Make sure regulator is disconnected (it will spark without it) but plug it back in when bike runs because it is there to “charge” the battery & provide “running” juice -> when bike starts.
- HT cap failure (common) – we use NGK to remmedy this. or measure resistance of the oem caps by themselves WiTHOUT the coil attached
(What is it under 20k ohms ?) - Ignition coil (common) , usually one of the first few mods changed on carby bikes.
Or measure their primary & secondary resistance) - CDI unit – I hope not.
- Wiring Harness – I hope not, only cross this bridge after dealing with the parts above first.
What year is the GV250 ? and show us the speedo assembly that’s on the left fork ?
One is digital , one is old gen black, one is old gen silver too (3 types were used over the years but they all fit, but not all work with every dash as every GV has seen slight revisions of their dashboards as time went on)
In my personal experience with ownership of multiple varieties (GV , GT and GTR)
I use these products all the time (plus the the bits sold at the shop section of this site, since i have to use what i preach)
- Motul 7100 , Motul 5100, Silkolene Pro 4, Silkolene Comp 4 = All in 10w60 grade or 10w50 grade. But 10w40 is fine all winter though.
Because the 125cc has a harder life, its a good idea to change oil every 1.5k miles with 2k miles being a limit.
4k on the manual is “too” optimistic because the clutch and gearbox start to get cranky/moody when oil has wanned after 2k miles. You want the transmission system silky smooth always and this means finding neutral while running won’t always be an issue. - Every bolt on the bike = Stainless or titanium, except suspension and axle bars.
It’s a must. - Use coppa slip on bolts that hold “plastics” .
- Use a “tear drop” of ACF50 on every single plug you encounter on the bike it’s a must.
- Google and buy on ebay “SUZUKI HARNESS” boot -> drop the oil cooler from its mount -> Hide the plugs from bad weather in to that suzuki boot.
- A 250 cooler helps 125ccs stay cooler. Especially faired bikes. and stops most mud trying to attack the carbs and rusting it up.
- “Any metal part” that moves (EXCEPT BRAKE DISCS) -> use Putoline GREASE on them.
- AutoGlym products are what i use to clean the bike and polish , wax etc.
It’s late but if i think of more times when my brain is a bit more engage , i’ll advise accordingly. Treat it well!
Hello , i have same bike and same problem my gd 250r is a 2017 model i swapped the baterry and it run well for almost a year now its the same cuts out unexpected. I´m wondering if its a fuel pump issue…
Clean the injectors and look at the fuel pump for any clogged debris or replace it, as sometimes it happens.
Also , check service manual and try to get Error Code from Dashboard to see if ECU stored any fault FI Error codes. This will make things easier.
You can also check / replace the relays on the bike. Fuel Pump relay can sometimes fail.Hello,
You can send me an email and I will do my best to order one in from UK trade or Germany and send it to you, i ship worldwide so its not a problem as I sell stators anyway from the shop for carb bikes. Getting a GD250 EFi stator shouldn’t be a problem 🙂
- Valve Clearances
