♠️ M77
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Yes you need fairings off, then use jacks to rise the bike up safely. Then remove the shock from under the bike , adjust it while it is out of the bike
OR if you have very small strong hands, go where the rear brake reservoir is, use a C-Shock tool to rotate the shock a few more clicks until the springs feel stiffer.
I think its time to rebuild the front cylinder
At minimum, you want around 125 PSI
Hyosung says the limit is 110 psi hot and healthy range is 140 – 175 psi
Here is a cheap front barrel and piston, it should be OK
https://www.ebay.co.uk/itm/256864818680And here is a spare one
https://www.ebay.co.uk/itm/255751060887I have confidence that either of the above will finally get the bike running.
Ofcourse make sure to get new gaskets you see on this shop
Rear is already at the limit of 110 psi but… If you have to do the rear, then check these out
https://www.ebay.co.uk/itm/256513929819Hyosung Korea isn’t making new pistons for carb 125cc or rings.
I am slowly researching and soon will test custom piston rings off another bike that may fit our bikes. If you just want piston rings, then i think you should email me , but stock is rare now.
This is why you can’t idle, the compression is too low.
Did you test the compression again one more time please and use the “METAL Pole” like this:
Use the Straight one with the curvy rubber tip, and press down hard on the spark plug hole.
Tell us the compression (even cold, although “hot” would be prefered as per OEM ) with full throttle and both plugs out.
Do this with a fully charged battery
Yes,
EFi cylinders have extra holes for E-AIS (electric air intake valve thing for fake emissions) and ET sensors (Engine Temp Sensors.)But yes you can use any 250 cylinders and plug up the EFi holes. Tensioners depend on cylinder of course.
I would not whatsoever use chinese carbs , many tried and failed. If Hyosung had to use a carb giant like Mikuni Japan, then it’s £600 new that’s what Mikuni Japan would want hundreds , not Hyosung as they still have to pay Mikuni to make us a double carb specifically for the Hyosung 125
What is actually wrong with yours ? This site has every possible part to replace its internals, all we need is your skeleton shell.
Something i’ve learned about high temps is the spark plug cap , i can’t remember if you have an NGK one fitted but the stock ones just aint good. Another thing to look out for is the ignition coil, it does happen too but less often than the plug cap.
the plug should be mud brown / beach seaside brown all the way , if unsure , post a picture of it.
Always a jaw dropping moment going through these Passes , good to see the bike out & about 🙂
Yup , just as Simon said , if its the carb float bowls or top diaphragm covers , then it points to the ground (road)
Fuel Tank Overflow = To the road too!
Not just the pilot jets clogged, but remember the “Permanent Jet” that is next to it? That is for starting and nursing her to idle back to Pilots. Those 2 cannot be blocked and including the passages inside the carb itself.
If the Pilots are clear, but also use Compressed Air with a straw, spray every little hole you see inside the carb until you can hear swooshing inside (pathway now clear)
Remove the intake manifolds -> Replace the o-rings (These little bastards) make the bikes hard to idle if they even so much as let some vacuum escape under there
If the o-rings are new -> Try to fully clean the surface where they sit so it’s 100% smoothed out. use a PLASTIC toothbrush and scrub hard (no wire brush!)
Then use a little bit of Engine Oil to dress up the o rings wet and install them back.
When it runs , spray carb cleaner around that area to see if revs rise again, then you may have some kind of crack on the intake pipe itself.
AirBox = Front Carb on front Cylinder ==> Check the airbox has fully consumed the front carb, if you see silver lip (carb top rim?) sticking out, there is your future idle problem there.
Final checks, make sure when its hot, do a compression test. I believe it really needs compression checking now.
Let her warm up 10 mins.
Both Spark Plugs out
Full Throttle
Crank It for 5 seconds
Get readings for each cylinder and let us know.I went all over the place in my reply but i hope i made sense.
520 Chain Kit & Clutch Upgrade.
The 520 kit is one of the best life changing mods for the GV125-S , every customer i know did not go back to stock 428 skinny chains & tiny sprockets.
Clutch = It just compliments the 520 upgrade, your clutch will have a bit more punch 👍
Exhaust = Get a garage to cut yours and weld a 51mm cone ===> Get / Find a full size 51mm exhaust muffler that you like
but remember All GV125 including 2001 models all the way to 2025 models will run SLOWER if you do not keep DB-Killer inside. It is because GV pipes are too short compared to Hyosung GT bikes, the GV models I tested (both carby and EFi) always hated it when I installed very small exhaust cans
Yes the noise is good , but the performance was rubbish. I used OEM exhaust and drilled a bigger hole for nice sound and the other bike I used OEM Harley 2022 exhaust pipes as a custom job.
Chinese cans from China = I did not care to try , they look like they will rust in 2 winters and look poorly made. The EU where we live is very salty and wet , especially UK!
If you want a good example of an exhaust that does not make your bike slow ==> Look at LEOVINCE Exhausts for GV125 and GV250 , then ask your mechanic to see if he can do something like that.
Whatever exhaust you have , make sure it is long enough to reach the chain adjuster
Keep us posted.
Your old battery may not be holding its juice very well (weak cells inside despite whatever voltage it says) , a fresh YUASA is advised yes (make sure it’s a genuine one from Halfords or TanyaBattery on ebay , other sellers selll either fakes or very old stock!) Time stood is the battery’s enemy, so the fresher the better.
Share this up on FB Marketplace or eBay or Gumtree , then post a link here, at least people can message you privately through those sites too.
Sad to see you go but hope your new ride keeps you smiling 🙂
Every Hyosung bike i’ve had to fix regarding suspension had leaked oil, it would be a nice surprise if they started using GAS instead of OIL. But their site still mentions oil use even for Cars / Trucks
Please do the tutorial , that would be a great knowledge base for the forum!
The reason for using a shaft & nut with a U bracket is probably likely that KYB uses that shock on a different bike other than Hyosung , so it may not be as exclusive as we think on the updated part, just the U part made for hyosung to fit our bikes. I have a suspicion Suzuki may still be using KYB shocks (as they did since the early SV & GSX days but different mountings & heights due to swingarm clearance , ours has a narrower clearance!) – the 07′ shock was overall better built but exclusively for 250R , i’ve not seen yet another bike use that shock.
Don’t change anything on the current shock right now , but keep an eye on the U-bracket , and improve it when the time comes. Spring position will not matter as long the big 2x nuts squeeze the spring more for a stiffer ride or loosen for a bouncier ride.
I’ve leaved over the years , that a slightly stiffer setting is best on these 180 kg bikes. I never felt comfortable riding even on the loose setting, the handling was just risky in the rainy roads.
For GV250 , it should be 92.5 and 95 mains. (This is even OEM size for 250 GTR too) , but measure your coils and caps , your sparks may not be optimal at the higher rev range.
Intakes post carb should be dry, so you MAY need to replace the float seats and float pins. The float seat has an O-Ring that causes internal carb leaks even if the bike is turned off.
Too much fuel dripping down the cylinders overtime is not good for piston rings & your oil will definitely stink of fuel next time you change it but i would change the oil now and oil filter as a pre-caution.
It is still made by Kayaba Japan , as they make all the forks and shocks for Hyosung (exclusively i believe, as I’ve not heard Hyosung use anyone else) though , it doesn’t shock me if Kayaba Japan used a china plant to make the updated shocks. It is weaker at the bottom yes. I would not try to undo the gold screw, may just be oil fill.
The spring adjustment (stiffness / softness) is on the 2x castle nuts resting on the spring itself. Further down makes the shock stiffer or further up make it very soft or very bouncy.
You can remove the bottom mount “U” shaped plate, that’s its only weakest point , otherwise rest of shock is OK. Get that duplicated buy someone else who does metal works and tell them to make the same “U” plate but 3x thicker & weld the nut for good.
What size Jets does it have ? Pilots and Main Jets ?. You could be over-jetted or the coils & caps are wanning (not as punchy as before)
I’ll be completely honest, I have no idea what size Jets. Spark seems good.
It is worth opening the float bowls and taking a look and let us know, and this will be a sure thing for you too, it may idle fine but as the road speeds go up, it may bog down more as it has too much fuel or otherwise try to get a meter out and test your coils with actual figures.
Ignition Cap Resistance (under 50,000 ohms) without the coil attached, just the cap. But i wouldn’t trust OEM caps to save my life anyway, so best to use NGK caps.
Ignition Coil Resistance (without the cap attached)
– Primary Ohms and
– Secondary OhmsIt could save a lot of guess work.
Could be coils ? I can’t remember if you have NGK caps , but if you have OEM capsd, make sure NGK caps & laser plugs are a #1 must have on these bikes because the caps always break down before the actual coil does.
If you already have NGK caps , check your coils. and caps with the comments i said above ^
Do this test and tell us the numbers:
– Idle => what voltage is the battery?
– Revving at 5,000 rpm => what voltage is it ?This is a charge system test or battery test , the fuel pump in those GV EFi machines draw A LOT of power hence 30 amp fuses or relays are used by Hyosung!
Any funny behavior with the pump => the bike quickly reacts strange.
Here is the O-Ring topic below (owner posted a picture of the oring that deforms):
What size Jets does it have ? Pilots and Main Jets ?. You could be over-jetted or the coils & caps are wanning (not as punchy as before)
Have you ever checked the ISCV (idle speed control valve) has an O-ring attached between it and the throttle body , it’s known to mangle up , so re-open and refit the O-ring with a little bit of grease.
If not, have you ever used “Wynns Formula Gold” as a whole bottle inside your tank and ride until the bike has 2 bars fuel left ?
(Wynns is good for bikes. Do not use redex ever. Wynns should help unclog your fuel pump’s mesh filter and injectorsIf you’re adamant the fuel parts are OK and are using E5 ?
Double check the ignition coil HT wire isn’t being vibrated out of the ignition coil itself , causes some sparks to arc’ out of the cap or coil.
Have a look at your spark plugs too, if unsure, take a picture and show us your spark plugs.
Oh you mean the “REARSET” unit , i thought you meant the “small pegs” that spring up where your feet rests on. Sorry for the confusion.
Try this one:
https://www.ebay.co.uk/itm/255149082615Thats my own stock, I have a few of them. If ebay is being difficult, send me an email below this site (Contact) for shipping fee.
