♠️ M77
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Will send you an email, sorry i had to remove your email in the post as it is a public forum. I may have a new mod for you to try, you might like it!
Watch a quick youtube video of the SV650 , it uses the same Kayaba forks as the GT650 (just different thickness & caliper mounting brackets & wheel spindle)
I know one of the 650 manuals on the forum has a guide for fork oil change but i can’t remember which one, so its worth a look ? Let me know!
Marcel thinks of everything
Haha , probably why my head is swelling like a hot summer melon, information overload!
Getting somewhere! Great news 😀 , if you can, use “contact cleaner” on every plug , trust me it should pay off, incase of oxidization of pins on cewrtain plugs , the signals shoulds flow steady to the ECU and various sensors on the bike. Let it dry for least 1 day so you don’t have wet pins connecting the ECU again (too easy to fry the ECU)
2K is good but a bit too hot for it for idling, if it can idle around 1500-1800 max, we’re good to go!
As long as you followed the tutorial , you should not have issues. Remember the “HUMP” side of the front sprocket that has numbers written on it must be facing YOU , then put the LOCKING washer on it.
“Rubber” on the old sprocket is just vibration damper , not needed as since the 428s rattle like skittles when shot up!
The “Holes” for screws on the sprocket means it fits a Yamaha bike. You have a hyosung which uses a BIG nut and a locking washer.
Make sure washer is folded twice and tightly hugging the nut, if you do 80+ on that 520 chain, you don’t want that nut big rattling loose! “medium loctite” also helps as an extra measure to lock thread. “red loctite (high strength) is even better and torque the nut to 60 ft lbs (google FT LBS to NM conversion if your torque-wench says NM instead of FT.LBS) this is to avoid you stripping the threads by being too tight!
Pictures of the VIN & Registration = send an email now (click contact at the bottom of this site), and I will respond, after responding you will have our email to forward pictures. Just need to keep your bike’s ID tags private from a public forum.
But yes we also want fitted pictures , i will use them on the Customer Shop Gallery page of the 520 kit 🙂
Chain Cutting = It is safer to use a “chain breaker” , since you need to remove one link and make sure the master link is safe to clip on again. (Don’t rivet the master link, as the master link is a “Clip-On” type, so don’t damage the little “fish hook” that locks it.
Again, before cutting chain, sit on the bike and ensure the tension is good , (about 20mm movement is OK) and make your shocks stiffer (pot hole country!) , that should make the chain less bouncy and saggy which would stretch it in the long run causing premature wear.
If you take a picture of your ECU , under the seat , i will confirm if it was an “early 2018-2019” model that was late registered. (Some dealers buy the bikes and they stay in showrooms for years until the owner buys it and they give it a 24 plate for example unless it was “pre-registered” as soon as it landed in the country)
Rear Sprocket = Counter Sunk bolts used by Hyosung as they made 2 hubs (strange if you ask me) , your counter sunk bolts will be better used on the 520 and it will lock the 520 sprocket just fine. (hence the counter-sunk bolt will sink in , as you screw in, until the 520 stops it. That means its locked enough, it will not rattle.)
If you see any rust , go to halfords and get Stainless Counter Sunk bolts for the rear sprocket as the back wheel gets a lot of dirt thrown at it!
Any chance you could send us an email with your registration and VIN plate , i will know if hyosung made “hidden” change to the swingarm again because I made sure it is the same chain we sent to other lads last week, no issues fitting.
If you are very sure the adjusters are maxed out, then cut 1 link. I really need to keep a long list of every customer bike that has a GV-S EFi and ask Hyosung why they keep changing factory chain sizes on the sly. It’s frustrating for me as a seller lol. Good job on the fitting though!
You could Amazon Prime 1 Day a chain “breaker” to take 1 link out or a local garage can do it if its a short walk ?|
BEFORE cutting , sit on the bike and check chain slack , should be around 30-40mm pushed up from middle of chain. (It can’t be tight when sitting!)
At the risk of being shouted at! 🤐 (as i know this means strip down time) – You may need to re-download the service manual on this forum that matches your bike (i uploaded loads of variations Hyosung made) and use a pocket meter to test every single electric sensor on the bike until you’re dead sure it’s all in spec
Fuel Pump = I haven’t got a conclusion yet but i’d keep an eye on it.
The ECU should be the last resort and it’s not exactly easy to get hold of due the 2009 type you have as Hyosung has moved on to 2014+ delphi systems. Though, if your bike starts and runs, i suspect to try and at least measure every sensor on the bike 1st before forking out money for another ECU.
Ok I haven’t had a chance to go for a ride until yesterday. It still backfires and misses and stalls. It seems mainly under 5 k revs. So I’ve checked all connections and replaced the coils, leads, caps and plugs and injectors. I’m thinking maybe the ecu is stuffed?
It may be your fuel pump wanning ? Have you got a new one to rule it out first ?
Start with this item:
Intake Pipe O-RING (Inlet Boot Seals) x2 – GV125 GT125 RX125 GV250 GT250 Hyosung
Clean and inspect your rubber intakes.
Mask the engine holes! (can’t stress it) then use a good old toothbrush (not a metal brush!) and some carb cleaner on the brush , clean the area on the cylinder heads where the intake pipe sits on.Then get carb cleaner again (3x cans, yes 3 cans…) = blow every single hole you can see inside the carb , there is loads of them.
Inspect the diaphragms and make sure the needle is at the “Middle Groove (OEM)” or “1 step DOWN facing the float bowl” using this guide.
[Tutorial] How to adjust Carb Slide Needle (Tuning) – Hyosung GV & GT 125/250
Get fresh rubber bungs below:
You WILL lose one.
Set mixute to 2.5 turns out each and do not touch it ever again unless i advise you to.
Get fresh CR8E plugs and go for a test run.
Keep in mind , if you open a carb , use “JIS” screwdriver , because regular philips drivers WILL round off the bolts and it is hell removing rounded off bolts!
Throw the bolts away and get these:
Stainless Steel Top Diaphragm Cover Carb Bolts Kit – Hyosung GV125 GT125R GT125 GT250 GV250
Stainless Steel Float Bowl Carb Bolts Kit :: Hyosung GV GT 125 250 Carby Models
When fitting your carbs to the bike, go to halfords and get “matching stainless” bolts for the intake manifolds after putting them new o-rings.
The carb must be on the airbox FIRST , screw tight (not too tight due to weak rubber holes on airbox) ===> Then hold the airbox + carb together and SLOW drop down to fit the whole thing in to the intake pipes.
Screw intake pipe clamps tight but not too tight! (These pipes are expensive and super rare now)
Consider checking your fuel pump and fuel tap = Both of these are at the shop ^ , overhaul it all
Consider also:
- Vacuum pipe (at shop) (tutorial here)
- Fuel Pipe and Large Filter (Hyosung says in their manual “any rubber hose” that’s 4yrs old (doesn’t matter mileage) rubber rots inside which will lead to eventual clogging of your jets etc..) (Fuel pipe kit is at the shop) (tutorial here)
Check your main jets and verify the last owners didn’t put stupid sizes on the carb making it too boggy to run (tutorial here)
What we have done here is “overhauled” the entire fuel system in time for spring season too.
Now, with that being said:
- Your compression is good! Engine is fine. (we will deal with the clutch later)
- Find time to do valve clearances (tight / loose tappets) directly affect how it starts and how it runs. Hyosung says every 4k they must be “checked” to be adjusted or see if they are still in spec. They are similar to the old suzuki “cam under bucket” style with shims, so familarise yourself watching youtube old videos of Suzuki bikes having their valves being down, then use the Hyosung Service manual for a proper job done.
- If the fuel system is all new and overhauled. Your next war will be electrics & air filter (air vs spark vs fuel) . you’re doing the fuel parts first.
- Oil = Motul 7100 is the MOST recommended oil for hot twins and i personally would not even dream of using crappy brands like Castrol Power 1 nonsense.
Silkolene Pro 4
Silkolene Comp 4
Motul 7100
Motul 300v
These 4^ should be your only options.
(Oil Change Tutorial here, because previous owners sometimes remove the wrong bolt under the bike and gearbox is gone!) - As per manual replace filter and o-rings everytime (see kit here)
- Fuel = E5 only. Forever. The carb bikes don’t like E10 and the power is just crap! very wasteful fuel.
- Flush = “ONLY THIS PRODUCT” <—- Do not touch redex! (Put £12 of fuel in tank and then pour the whole bottle inside tank, ride as normal!)
Unrelated but possibly related?
– Choke Cable ? (kinks or frayed may make the carb not fully close the choke)
– Throttle cable (same reason)If in doubt get both new cables from the shop, your throttle will be more snappy and smoother on your hands , so you can actually feel what’s going on.
Hope this helps and good luck! Keep us posted.
why dont they like wheelies seen people do it before , does it put oil in wrong places or something ?
– Forks not made for wheelies , it barely holds the 180kg bike without bursting oil seals.
– Engine does NOT like to run dry when oil suddenly sloshses away from the spinning parts that need constant lubrication (cam chains, tensioner, clutch basket , bearings (again bearings!!!)
– There is no other 125cc you can find that has a lot of bearings inside than the Hyosung does, they must stay soaked in oil all times.
– Oil Pump doesn’t like to push itself too hard, it’s small but enough to flow around , when the engine is hot the oil pressure drops to 0.5 megapascals ( i have my own donors fitted with pressure gauges so i know when its low or high) , 0.5 is when it’s idling hot but can wane/hover around 0.3-0.6 , you wouldn’t want to drop a clutch and wheelie off when it’s that low. It’s normal 0.5 as the bike is idling , it will pick up when the rider gets in gear and rides nicely.
– Top heavy girl, i’d rather do it on an SM bike.The guys that wheelie 125r’s are not friends you want when things go wrong for you. They don’t care 😉
Front 2.0 Rear 2.25 How can I check if these settings are correct? Do I need to look at the color of the spark plugs?
Fresh CR8E plugs, go for a nice ride and come back to show us the spark plugs , i will tell you if the mixture is good 🙂
When it runs , tell us the voltage of the battery at idle and also at 5,000 rpm. (Regulator test)
Fuel Pump Relays failing can happen but its not uncommon , the fuel pump draws a LOT of juice all day long. Replace with a new relay if in doubt and also make sure the contacts are clean (while you clean every plug on the harness.)
You will be amazed at even a rusty fuse can cause a 1 (one) volt drop enough to cause problems in the EFI system or a fuse that’s too old, replace fuses as precaution, the harness should have more stable juices flowing everywhere now.
Then recheck ECU for any codes later.
they look ok dont get me wrong but im worried if i ever dropped it there would still be damage may have to do lots of measuring up, plan on trying to wheelie it at some point anyway just cause i can lol
Please please don’t wheelie it! , you WILL regret it. Even the SV650’s don’t like wheelies either.
A DRZ400 SM? yeah sure go ahead!
It may sound silly, but can you get carb cleaner ?
And do this outdoors due to vapors! ==> Spray the intake system in different spots to see if revs change
If idle takes long to return to normal after a high rev = air leak or ISCV unit possibly (but another air-related sensor may be involved that’s on the throttle body such as TPS)
If if you quick twist throttle and it dies = Injectors (clogged or underperforming (wanning) ) or else the fuel pump is wanning? or else again intake system (throttle body and its ancillaries attached there)
Air filter should be clean if its a young mileage bike (if under 10,000 miles , air filter should be fine unless there is some unexplained damage to it)
Let me know if the above ^ even helped make slight changes (then we are getting somewhere)
If possible, remove harness => clean every single connector you can find (resistance or voltage loss can happen along the lines to make certain sensors on the bike perform less than optimal , in thus the ECU may not always overcompensate for this)
Also , test your stator (importat) and your regulator (way too important, probably the #1 electric device every one discards for a better one)
Battery should be new (where possible), as it’s 2025 , give her a fresh one and make sure it’s a genuine YUASA one (USA brand) , not too keen on other brands (chinese crappy cells)
That’s a fair point there! – Not seen such pre-made cages you speak of, so it looks like a custom job if you’re not keen on the simplistic R&G Crash Mushrooms they sell.
For what reason would it need one ? It seems the fairings already shield the engine (not perfect but still plastic!)
Also R&G UK already make large crash protectors that go through the fairing incase the bike drops on its side.
There isn’t an “off the shelf” pre-made cradle / engine guard for the GT125R
As its a security issue, and being a public forum. I locked this topic to continue this privately.
Send me an email below , and I will discuss what we can do for you (unless your dealer or insurance company can help you?)
Thank you, Marcel. It’s only been a few hours, don’t apologise. Order was made today around 2pm gmt to Bradford, BD4
Thanks again!Bare with me for 3 days (By wednesday i should be shipping it) because I need to order again the special rear sprocket (There is only 1 company abroad that makes it for us so far), a customer took our last stock we had on the shelf today funny enough. So I will need more sprockets!
Hold tight, any “tracking alerts” will be sent to your email.
Hello,
No need to cut the chain, we will do it for you.
Hyosung went from 140 links to 138 to 136 , so it meant some “early” models had slightly longer chain adjusters on the swingarm.
Your 22 plate will be fine! Email us if you have other sales enquiries, it will be quicker since it concerns the shop parts.
Sorry for the delayed reply. Long day!
Sounds stupid but is there any way at all you can get the bike warmed up for 5 mins hot
remove both plugs out
Put a compression tester in front engine , crank full throttle for 5 seconds.
Do the same for rear engine.
Can you tell us the compression figures.
I feel like it is very important to start there 1st before i would advise anything else for that matter.
Similar issues last week , a client of mine said he needed a new engine which we helped him get despite me cleaning his carb & tuning it twice. His rear engine had low compression!
I hope it is not your issue but it is usually overlooked , she’s a big girl!
Regards
