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Hey,
Good pic but i couldn’t see the rest of your bike setup where did the other pipes go, what happend to the other throttle body?
This is the setup for your 2008 bike,

Also take note , the rest of the pipe set up that follows the AIS (egr / air valve system) device

The sign of high revs could also mean the air filter has rattled loose ? (Inspect the filter bolts) – When taking out throttle bodies, inspect their o-rings like image above.
I know for a fact this also happens on carby bikes with leaky o-rings – They rev high, the rpm needle takes a while to return down to idle.
Aug 26, 2018 at 1:33 PM in reply to: [Tutorial] Hyosung GV650 & GT650: Tip Over Sensor (TOS) Bypass Mod & C23 Fix #1680Hey,
According to the manual – The RO Switch (Roll Over) aka. (TOS Tip Over Sensor) is under the seat.
It should be near the battery, if you read the above ^ pdf file, you would have a visual idea of where it is.According to the service manual (EFI), this is what it says:
“CHE” : The LCD panel ① indicates “CHE” letters when no communication signal from the ECU is received for 3 seconds.
C23 = RO/TOS Switch faulty.
For a more detailed explanation. Download the link below and go to pages:
#27, #34, #47, #66 ,
– Service Manual Link –Personally I don’t have a TPS sensor on mine, if it did, i’d find ways to get rid of it myself. But i have no experience in using other brand manufacture TOS sensors on a GV650
However, the above ^ book at the top, does mention that you may use other brands from “EFi/Ei” (injected bikes.) Designs may also vary too.
This is the most recent TOS sensor hyosung uses that I know dealers to be stocking up,
Hope this info helps, let us know how you get on!
Seems to be an expensive part for a genuine backrest from Korea. About £165-175 new if i was to import direct!!
Quite a rare sight in UK though!
You can also “try” asking too in the facebook group incase someone may be breaking a full aquila
Hey Pete!
Great questions there. Hope this answer helps!
- ALL “GT125” since 1998 use the same coils , same CDI , same regulator.
- They started with a small grey regulator –> then they tried a slightly bigger black regulator a few years later (since 2010 i should say)
(but both fail too much!) They can’t even do 14.6 volts! - They tried to use a newer coil from a 250-EFi (which also works with Carb bikes)
However, no power difference whatsoever.The upgraded reg/rec uses MOSFET tech regulators, which are much more efficient than 1970’s serial/diode tech (Hyo). Very common on big Kawasaki machines, so you know the Japanese don’t like for things to fail.
And I know Kawasaki machines myself, so i studied their electrics in comparison to hyosungs. For example, I would know which pins are plus / negative , how much volts per wire etc…
650 owners = 2 major mods they always do = Drop a 250cc Ninja Magneto & Regulator as the 650s REALLY do cook their stock regulators , so an upgrade was necessary. Hyosung would just keep on sending the same stock ones which would again blow up. No change.
125ccc = All standard hyosung regulators cause so many problems, it’s beyond belief. Just go on our facebook group, also chinese versions have set the bikes on fire & smoke on dashboards.
So I never ever sell them, (too much liability) – Kawasaki tech wins.
Wiring Harness = 125GTR / GT125 Nakeds (all) – Same plug, No change whatsoever.
Ignition Coils = Also a bolt on fit , just look at the shop gallery, so many bikes 2007 plate , 2016 RC , 2012 model etc… Kawasaki race parts here again.
People tried Suzuki SV650 coils on 125, they don’t work. Placebo effect lol.
Remember, no one goes to a mechanic under my watch, I got you! –
For a total novice biker Even clutch change was done at home without paying a random mechanic £200 to do it!Oh by the way! – It’s a great shout check your spark plugs , if they are the “stock ones” (CR8E) – Just bin them. Too heavy & fouls too much.
“CR8E IX” (Blue iridium) or CR8E-Lasers work best! – The coils & reg rec work best with IX or Laser plugs definitely.
Remember, this colour below = a very happy hyosung motor (Good sparks, fuel, air)
(All coffee brown ring/dark biege center)

If there is anything i missed, just let me know! Have a great weekend.
Hey, tell you what…
- Grab a multi meter -> switch to DC 12V (Volts)
- “Bike Off” = battery should be 12.8 (“minimum”) 13v is good.
- “Bike On” = battery must NOT drop below 12.7 whatsoever
(it won’t start on even 11.9v)
Then we know the battery is “HOLDING” charge regardless if you switch the lights off.
If the lights “DIMM” when when you switch them on even though bike isn’t starting = the battery has gone bad. (the lights are a good example of how much power they draw)
When you press the starter button with a weak battery = you will hear loud clicks from the “starter motor solenoid” or it won’t act at all.
Once we have solved the battery issue.
The solenoid immediately should spin the starter motor as soon as you touch the starter button. No delays about it.
If the bike cranks “slowly” – Investigate these 3 in order: Dying solenoid (too common) , starter motor is dying out if its too old or too worn internally (a lot of uses in a short life of the bike) , and lastly the battery (may be sending low current) (weak amps through the wires)
Battery is 12AH/14AH // 180-230 CCA (Cold Crank Amps) (this is starting juice)
Code is “14BS” (eg. VARTA 14BS)Also a local garage should be able to “test” your battery for its internals (not just volts) but wether it needs replacing overall (dead charging cells inside.)
I hope this info helps, but let us know how you get on pal!
Jul 31, 2018 at 11:23 AM in reply to: [How to Tutorial] How to Swap Upgrade Carb Main Jets Hyosung GT GT125R GV250 GV125 GT250R #1597I think your “float bowl” gaskets are leaking or the bowls aren’t screwed in tight (maybe one bolt is looser than rest)
I’ve seen this happen a few times to some , usually you can drain the fuel again…then expose the carb bowls.
Investigate the gaskets. If they look crushed or flat, they probably need replacing.
Or re-tighten each bolt that is on the float bowl.
A leak does prevent start ups.
Also, i’d 100% recommend changing the oil as soon as possible , as any wet fuel pouring down the piston chamber, will mix with the oil , glaze the piston walls soon.
Any recommended place to get SS ?
Do you mean stainless exhausts?; I’d say Black Widow UK definitely, some folks have scorpion pipes fitted on.
As for bolts, a local bike shop must have a tray of exhaust bolts as they are common replacements for rusty ones…
Stainless = only the “threaded” stud can be found in stainless form too.
Not stainless = the original hyosung TALL nuts , for these sand them down and apply vht paint, when you’re cleaning the bike on a regular , a tiny dose of acf50 on the bolts and the pipes, that will burn off , but leaves a tiny film over them. Another way to avoid more weather attacks on the pipes.
As for the tall nuts, only hyosung seems apparently to be the only source. So dealers have to order them in , you may find used “hyosung exhaust nuts” on ebay that aren’t too ruined, may still have some life in them. Expect to repaint them or treat the surfacing rust
Hope this info helps!
Whoaa….. I say that looks really bad!
Do you think you’re able to get a exhaust shop local or a garage to extract the “likely” seized bolts at the engine ports.
Or try , if you dare , the front engine is usually prone to rusty bolts & pipes sometimes from salty muddy weather!
The reason i say this is because it’s easier to remove the exhaust system off the bike, then get a way to get it welded (costly) / sleeved up again.
i have seen people also spray a lot of VHT black paint that is supoosed to be weather resistant. Then they wrap it up with exhaust wrap all over.
More than likely you will be looking at fresh studs & bolts anyway! – Stainless is the way to go!
The stock hyosung exhaust pipes have 1 big outer shield (which is whats corroding away) & 1 small “inner” exhaust gas pipe that the engine uses…)
Haha hey Deano!
Welcome to the forums, I can agree if i was you I probably wouldn’t stop smiling either!
But no matter the time, better later than never, i am sure this time you ain’t getting off the bike anytime soon lol.
Ride safe pal – I hope to do a meet near the scottish borders to meet some of you hyo owners living in the higher lands!
Jul 27, 2018 at 8:56 AM in reply to: [How to Tutorial] How to Swap Upgrade Carb Main Jets Hyosung GT GT125R GV250 GV125 GT250R #1577Hi, im New to motorbike mods and may seem like a noob question but where do you get the jets from because I’m seeing sellers asking to make sure there the right size as there all different, also looking on just eBay for k&n air filters it claims it makes no difference to a stock setup are they worth getting if I have ss pipes, thanks in advance
If you can’t get Mikuni jets for your bike , just email me and I will find out for you.Do you know a local bike garage that keeps a stock of jets as the Mikuni brand is used on other bikes too. I always send out some bolts, ebc jets & filters to some who already have ss pipes.
If you get jets from another source, be wary of cheap china brass as they gum up easily!
Can be a nightmare cleaning them out haha.

K&N 650 filters push about 2/3x more air than stock. In fact, the stock setup already needs bigger jets as the factory versions are too small.
If you have SS pipes or K&N Filter (whichever comes first) , jets will need to be changed or there is a risk of overheating the rear or piston wall glazing.
Take out your spark plug – this colour below (coffee brown) means fuel / air / exhaust system is optimal.
Center is “CREAM / BIEGE” in real life.

If its a pure white colour in the center, then it’s lean, which doesn’t help with the risks i mentioned above ^ ^
If it’s sooty black = that means it’s rich, the fueling system needs cleaning (carbs in this case) or plugs / coils need inspecting or it’s getting too much fuel with less air (clogged filter)
Hello. Yeah just email me about the GV chain upgrades. Its a special order as 520 rear sprocket is custom made in the US 😉
So it will be a game changer when many gv riders have done away the fragile slow 428 chains.
Your parts have been sent. Expect them tomorrow hopefully.
Valve clearance schedule is:
600miles (1st service) , then every 4,000.
I hope your mechanic knows his way around hyosungs (they are still a suzuki intruder engine but evolved better by the Koreans).
Lincs isn’t far. If you need me , just give me a shout , be happy to show you how things done anyway & what to watch out for etc..
Have a good week!
For the coils,
1. Grab a multi meter
2. Red wire on the HT LEAD
3. Black wire on the spade-terminal of the coil.You must get 5.0K – 6.2K Ohms maximum. That’s a healthy coil, any values beyond that, the coil needs replacing as they can’t be repaired.
5K = 5,000 ohms.
Like my example here..
(Black wire from your meter must test both the “terminal” spade and “fins” (where bolt slots through)

Take out your spark plugs , this image below was my laser iridium plugs after 2 years (20k miles) .
COFFEE BROWN = Healthy fuel system including your carbs (optimal)
BLACK CHARCOAL = too rich or carb issues inside (gunk?)
BLACK & WET = fuel smell = coils are not working or plug itself is shot.
BLACK & OILY = piston rings (God forbid!)
WHITE CENTER = too lean… that will kill piston rings very soon! (Suspects = carbs , coils & plugs)In all cases the last 2 are critical and no one want’s to be there… better to be richer than leaner…

You said you only had it 18 months. How many miles is it done so far ? & does it have history of service inspections concerning the check for plugs , air filter clogged , and possible check on coils ? if it was behaving erratic in the past before ?
If it was a new bike, the dealer would “have” to fix back to standard again as part of the warranty.
Pilots & Starting Jets (2 other tubes next to main jet) control starting & idling , slow running until main jet takes over from 2nd gear ish or full open throttle.
Get a CLEAR hole , while cleaning , like my example below:
Pilots are VERY notoriously easy to gum up! –A big fuel filter helps a lot prevent gunk going to the carbs in the 1st place.
A clean air filter is also important! – Some clogged particles do get sucked in!

“STARTER JET” is the jet that can’t be removed, but compressed air with a straw can blow hard through it or a carb cleaner is best. The hole is much more tiny than the pilot!
Hey,
That’s cool, let us know how it goes with the new mechanic in the future, but i think i am confident you can be able to keep most tasks done yourself.
Keep receipts of whatever you buy & save it in a book somewhere, it’s something I do in case i have to sell it, i have receipts of whatever parts have been added & the mileage at the time.
Valves are checked 600 miles, as it’s important to ensure the engine isn’t tappy, ratty or loose cams etc… The first 600 miles gives the chance for bike parts to mature up inside and mesh together nicely
So after 600 miles, it would not be surprising to see some metallic shavings on the oil , once you do a fresh change.
How many miles do you do each week anyway?
Speaking of upgrades, honestly speaking, the mind is the limit but based on various feedback online, i know these mods are the “most obvious / most effective” upgrades meaning you will notice it outright & perform way better.
- 520 Chain Kit (Converts 428 chain to a fast 520 chain system)
- Large Kawasaki regulator
- Kawasaki ignition coils
- NGK CR8E IX or Laser Iridium plugs
You can read more about the first 4^ popular upgrades via the shop link below:
https://hyoriders.club/shop/GV Aquila chain kits are a custom order, (no one does 428-to-520 kits besides myself), so send me an email!
5. Then also importantly (stock or modified bikes) – Upgrade carb jets to one size up…
I have written a full tutorial below , so you can see how the process works.
Easy to do! (if you need jets, just send me an email or ask your mechanic)
Your carb is Mikuni BDS26-DOUBLELink here:
https://hyoriders.club/forums/topic/tutorial-hyosung-gv-gt-125-250-how-to-swap-carburetor-main-jets/Hey @sebringmaster
Let’s try another method now,
- Go to halfords locally, grab a can called BRADEX EASY START
- Lift up your fuel tank
- Spay lots & lots of bradex in to the air filter hole.
- Fire up the bike, hold the starter for 7 seconds max
- WHILE the bike is “cranking” -> keep twisting the throttle multiple times…
- Once it fires , use full choke until it warms up for 10 mins.
…..failing that….
Run to halfords or eurocarparts or MotoSave again,
- Grab a pair of NGK CR8E IX (Iridium plugs)
- Connect 1 spark plug to the “IGNITION COIL HT LEAD” (HT Cap)
- Do not FIT spark plug inside engine.
- Leave the plug exposed while connected to the WIRE HT LEAD
- Switch on Dash. Put bike in neutral.
- Put the SPARK PLUG AGAINST the “FRAME” or “ENGINE” (Avoid PAINT)
(Look for a metal frame part which is not painted) - Press the starter button (keep the plug on frame)
- If you see “SPARKING” while it cranks ….
- That means THAT COIL works.
Repeat this process with another COIL.
What we have done above ^ is checking if your ignition coils front & rear are actually sparking good.
if there is a weak spark. It is probabaly the coils trying to give up the ghost or behaving erratic (very very common on stock hyo coils)
Battery:
OFF = 12.8v / ON = 12.7v max (it must NOT drop by 1.0 volts)If a battery says 12.5 or less while on (without cranking motor) = Investigate the battery , local bike shops can test your battery to see if the CELLS inside actually hold charge or quickly loose their 12v juice (not matter how charged up it is, the cells must hold it)
Remember = GV125 , GT125 Comet & GTR use identical engine, identical coils….
So please have a read on these links where i gave more detailed response to the others,- https://hyoriders.club/forums/topic/hyosung-gt125r-starting-problems/
- https://hyoriders.club/forums/topic/2008-gv125c-headlight-running-issue/#post-1293
- (Best one) = https://hyoriders.club/forums/topic/hiyosung-125cc-gv-running-slow-when-warm/
One thing to always remember =
High Revs / Hanging needle = Air leak somewhere / carburators probably messed with.Boggyness / jerkyness / cuts = Electrics & Fuel.
Common cuts are usually coils , fuel tap , clogged filter & rotted lines , carb has foreign gunk clogging its jets, side stand switch, clutch lever switch
For more reading on carb 101 , check this out… (I talked about jet sizes & pilots)
[Tutorial] How to swap Carb Main Jets – Hyosung GV & GT 125/250
Report back and let me know how you get on!!
Last tip! – Remove the front spark plug -> spray lots of bradex INTO THE HOLE (in to engine) – > reconnect the spark plug -> Fire up, and keep the revs up…. till it idles nicely to 1.7k rpm (best spot)
Go to fuel station. Fill up 4 bars of fuel (£4-5) , and buy REDEX 2 SHOTS (2 small bottles) -> Fill all of it in to the tank , so it mixes with fuel.
Ride your bike until the fuel level drops to 1 bar…. We have to see if redex can help attack all the gunk that travels on the lines, filter, and also attack gunk in carbs, so that once it hits the piston, the get burnt off by the plugs.
Personally once a month, I use LiqyMoly (german) , same as redex but for bikes with extra additives, the principal is the same. It means i have less maintenance work to do with carbs.
Good luck!
Hey Nigel!
Welcome to the site & forums. I hope you are also part of the Facebook group below too:
https://facebook.com/groups/345623961212/There is quite a lot of GV125 and GV650 owners popping up this season too. It’s not just hyosung sports bikes being famous now!
Moving on, let’s talk about your garage/dealer first!
For me with just a couple of years experience with the Hyosungs (knowing how every part works) I can honestly say this… Your dealer is an idiot.
If you have a bike under warranty for that matter, everything has to be recorded. What happens if you were to sell it and how can you prove what has been done and what ?
Also, they must tell you WHAT justifies spending £75 on what ? I can almost 99% assure you, they work on “budget” basis, basically they use WORKSHOP OIL (cheap artificial oils) …. Yet the manual says use GOOD premium oil. There is a lot of moving parts & bearings in these vtwins. a lot! Good oil, filter, o rings goes a long way
Myself, I do travel to some distant places to rescue some GTR bikes as a mobile mechanic, I can stress that it is always good to check everything on your bike if something is off. It’s good to address it before it gets worse! That saves a lot of bills in the long rung and a happier bike when the owner stays on top of things.
I’ve seen too many mechs take shortcuts, it doesn’t take long for each owner i meet to have a long rant about how they got ripped off in some places and ended up worse off lol.
I’ve never lived in Lincolnshire personally, so i wouldn’t know who is a true bike mechanic.
Ask in the Facebook group, as there is many lads who live there but most actually do the work themselves by following manuals.To be fair the Hyosung’s literally last quite a long long time even 10 years @barry650 has one. On his 650, all he did was change regulator for aftermarket ones to keep the electrical system happy, the rest was just regular maintainance. Ive had a 125 Aquila that was 51K and 2005 reg. Old girl still had life in here!
My local dealer services some Aquilas that are usually 30K on clock, you can tell the owners have been riding all over the place without killing them.
Speaking of that, check out the links below for service manual & “owners” book.
Service = more detailed / Owners = common things to do.So i say read all links, remember GV/GT250 engine works the same way as 125! – Just bigger pistons & a larger cooler. Same valve clearances / same timings.
OWNERS BOOKS
(Download the “2003 Onwards” models):
https://hyoriders.club/forums/topic/download-gv125-gv250-aquila-mirage-service-manuals-hyosung-owners-books/SERVICE MANUAL (ENGINE WISE)
(Download the GTR & GV250 EFI SERVICE manual) – For detail engine work/ specs.
https://hyoriders.club/forums/topic/download-gt-gtr-125-250-r-comet-service-manual-hyosung-owners-books/Coming from a guy that once spent 6 months average tinkering with his own cars in the past, I am glad to say “I agree with you Nigel , biking is just better”
Cheaper , more satisfying when things are sorted & more LIBERATING… (I am sure @bigtrev1969 can confirm this haha , i know how much he likes tinkering with this Aquila by himself , than trust some chinese to do it, i had to mention him!)
Ride safe fella. Hope this info helps you, if there anything unsure of, just let us all know!
Hey,
Personally if you go on Facebook group and search “520 chain marcel” or something like that. Everyone always has big praises for every tailored chain kit sent to them. It is their favourite mod on the bike by far.
Most common replies / feedback are along the lines of:
– much faster acceleration ,
– bike still sits at 70 all day & gets there much sooner
– max chain & sprocket speed limit is 91 – 107 (125 & GT250cc bikes)
– japan 520 kits outlast any expensive 428 on every hyo. (less chain adjustments!)
– Made for serious touring , 428s are prone to snapping away wheres you can do even 400 miles in one day with a 520.Put it this way, stock machines max out 82 – 88 (GT125 & 125R) – With a 520, you will get to 80s much quicker & not worry about a chain snapping on the way to scotland/wales for example.
Personally, I went from near York (north) to south Bristol (500-600 miles round trip) , the chain kit didn’t flinch or bother me. This is doing top gear all day on the motorway as a demo test. I still have the same shiny rear sprocket 1 year later, and still is good to this day. i’ve seen crappy sprockets fade so badly after few weeks lol.
I have not seen anyone else do a better bundle, as i’ve seen some sellers put useless sprockets with virtually no difference to acceleration (defo not a “race kit”) , besides that they don’t even include washers (mandatory replacement) or even high strength stainless bolts knowing our old hyo-stock bolts will crumble away in rust lol. Watch out, some chains are heavy & use fake metals. (Especially chinese)
Ride steady!
– MJust found on Ebay for £3.05 =
BLACK Silicone RTV Instant Gasket Rubber Sealant Waterproof Adhesive 40g Tube
I’ll give it a try.
That should work.
If you can, take a photo of the situation. Then access this forum via a mobile device , tablet or pc – Then click “Add Media” at the top to attach a picture in your replies.
It’s just strange what has been done to the bike! bit of a Frankenstein situation there!
Love it. Love it. this inspires me to do my aging 07 frame in deep cherry red.🎯
Did you strip your frame paint before this?
It will discharge slower when kept in a dry place disconnected.
Or a bike trickle charger helps too!
Reason I didnt mention cars is due to the huge amounts of current that passes through the car electric system (too strong for a bike battery or bike loom)
Some cars can fry up a bike harness ( they are only rated 10amps mostly) when the car is on/running.
It is OK to disconnect the car battery. then join it to the bike ONLY to start it.
Once it fires. ride 10miles, the magneto of the bike should add some battery juice by then (charging)
Welcome pal!🏁
Loving that SM! not many left in UK and i want one tbh.
100% agree the exhaust needs changing, not just for looks. be nice to have a bit of extra oomph to it
Oh yeah for jets. Go one size up! 👌🏽
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