♠️ M77
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It will be hard without doing custom work to the bike involving some kind of piggyback ECU or aftermarket part to make up for the fact that airbox deletes means more air in the system but injectors are still flowing at the same rate. Engine will cook slowly and if the exhaust is too short , it affects backpressure a little bit , so it may feel a little less torquey or more “flat” if you will.
Perharps , find lighter exhausts off recent harley models and get someone to fabricate custom headers , if harley can get away with using slimmer pipes on a delphi unit ( i believe one of their models uses a delphi unit) , you could rob their exhaust setup but… the ecu may be tuned by them to deal with it. Unless you know how to access the ECU with a PC or know someone locally who does harley flash tunes, he may take a look at your ECU , do a few dyno runs with different setups OEM vs Aftermarket parts , they can tune the bike appropriately. There is a guy in Australia called Hyosung Performance Tuning , he loves his GV’s and is know to flash tune ECU’s (I dont know if you are close to him or not, as you did not mention location in your post) (Don’t worry I am fixing the forum profile pages this week!)
Pod Filters = Hyosungs have historically hated them and always ran rough , i suppose you could leave the air system as it is since the big box is tucked away under the tank and the airbox above the engine doesn’t weigh much, the bike won’t notice that kind of weight unless you are racing on a track where every milli second counts.
Biggest weight is also the wheels = here this is a totally custom job on how to find light wheels off other bikes and retrofit them to the Hyosung (lots of studying + trial and error here!) also keep in mind the speed sensor on the front wheel wants a Hyosung rim , it won’t spin on other rims to count speed unless you find a 1:1 replacement rim that slots in the Hyosung speed sensor without messing around.
Just some thoughts at 1am (im about to head to bed haha) & some ideas here! – I may have a better answer when I am more wide awake
Hapy holidays & new years 2025 in advance!
Video sounds good. I hate to say it , Historically Hyosungs since 2000 have always hated pod filter setups , so maybe start by putting the original airbox back and original filter?
Also if there is too many changes to the air system = ECU will not adjust completely as Hyosung themselves set the ECU to expect to run efficiently on its OEM parts including the injectors (i am currently studying upgrade options to the injectors so that they output a little more fuel to stop the bike leaning out on full throttle)
I would also advise doing compression tests after the engine is warm with both spark plugs out. You said it was getting worse , we don’t know if your compression is getting lower (due to bike leaning out & running hotter from that air system change , thus piston ring woes likely) . Maybe on rainy days , some wet air was sucked in to the engine over time (it looks exposed)
Just some thoughts here , keep us postedon that video situation
Can you elaborate on what it is actually doing from the moment you turn it on ? and how much of a mood is it in while riding before it gives up ? So i can point out what the issues might be. Even information on how it idles on stand still ?
What colour are the spark plugs ? are the CR8E or some other code name etc..
Did the coils change? (rear one fails commonly, so do a swap test)
Does it have black HT caps ? (get rid of them and use NGK ones!) – Nothing but trouble those thingsYour ECU is discontinued, it’s the early type (circa 2017-2018) , before they all changed to the updated delphi units including all wiring harnesses changed (not backwards compatible) and most sensors changed. The fact that it runs (even starts the bike) means not all hope is lost on that unit. So i would address it as last item to worry about
Can you post a picture of your ECU?
There is no public wiring diagram as of yet but then again, it shouldn’t be too hard to fix unless the ECU is toast.
It’s best you make a new topic if you can please , so it’s easier to follow your bike alone. 👍
Happy holidays!
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Topic closed, as Simon replied to a duplicate one you just made.
Ride Safe!
I would be shocked as to why a NEW gasket kit would cause a bike not to start again, that’s bizzare! – He did something that he does not want to admit , because it’s a GV Aquila 125 Carby, let me tell you this … It is VERY stressful to “perfectly” align the airbox , hence we did tutorials for it.
I suspect….
- Intake O-Ring has smudged or crapped up , during refitting it (if you see our tutorial , you will see why its an easy mistake to make)
- If he didn’t remove the carbs or airbox out of the bike, and did the rebuild kit while the carbs were in situ, then likely floating dust got in the carbs before he closed it all up
- The “middle big snorkel” that connects the top airbox and the side-right airboxes may be loose.
It sounds stupid, but I’ve worked on many customer GV125 bikes, they are VERY fussy to start if something is amiss during refitting parts back, so it’s worth having a look, and if it does run, you may be leaking out air or loosing vacumm through one part of the intake system that’s loose or missing (ie. o-ring under in the intake pipe by the cylinder heads)
Maybe the fuel filter is facing the wrong way when the tank was fitted back in ?
55=60 mph uphill is decent, and now it’s doing less, i would get the mech sort out what he did and pay the collection fees.
As a side note:
- When it’s warm , get compression readings (important!) = Both plugs must be out , crank bike at full throttle. Tell us the PSI on each cylinder
- Valve clearances ? (as per manual its around every 4k to inspect or change tappets) (The longer it goes without it done, the more MPH it looses and it gets harder to start)
- Clutch = Big girl fella, the 125 plates wear down almost the same rate as the front caliper pads do , hence manual repeats that around 4k ish , check the clutch “measure the plates” , and “measure the springs” , clutch fatigue will drop power.
Simon’s right though , takes a day to sort the carbs out , unless he was waiting for parts or doing engine clearances the same time (since engine was exposed, would be a good time to check clearances as a good measure for servicing to alert the customer if engine still in spec or not)
I don’t know what your local stores are like in Australia , but browse the shop on this site and see if one of our coils matches your bike (Hyosung makes different ones based on ECU, ie. Delphi takes Delphi coils which we have started to list this week) , or an NGK wholeseller locally and show him a picture of the NGK caps we stock up , that’s if you are in a mega hurry
WhyGoStock does similar if you want to use a US source , i rarely mention other sources like HyoAU, HyoNZ , HyoEU etc as they are the same design , same scammer that loads of people have complained about.
Magnecor HT wires are common on Amazon UK, so it should on Amazon AU ?
If not send us an email if need anything from us.
Or , try a local salvage breaker and go to their bikes in the yard that may have 2nd NGK caps on them (just avoid plastic caps as they WILL crack), and possibly a Hyosung that has the same coils as you, take a meter with you and test their resistance if they allow it.
It’s the Xmas rush & new years, so things are a bit slow in UK even to ship stuff abroad ourselves, if you don’t mind the extra wait.
Hi Marcel, hope all is well. When attempting to start the bike, no fuel leaves the tank. I also used “mannol 10w40” intsead of the recommended oil. Im going to put a new oil, fill up the tank and attempt to start again.
Low vacuum (intake oring leaks) as per my earlier comments above ^ (or just see this link directly below)
Or tap issues.
And yes as long as the oil says JASO MA2 for motorcycles (certification) otherwise it may be car oil & you will have a lot of issues later. If it’s bike oil, i would replace it after 500 miles and use motul. It sounds crazy but most people who say “any oil is fine” are the ones you wouldn’t want to hear their advise on serious matters anyway lol
If not , i would find a GOOD working OEM cap for now and use MAGNECOR HT wires alongside your new coils (replace both)
You got it! – If the coil is intermitent (haywire or chaotic) it will behave as your video did. I would replace the coils and try to use NGK leads and NGK caps (The OEM Caps are too problematic to reliably conclude the matter as resolved)
The starter motor’s body was a hyosung creation to make it fit on the GD engine as it is one of a kind, but i can’t “confirm” if it is possible to use the “internal parts” off the GT250R , or 650 or the MS3 scooter. The MS3 is very rare now but shares maybe one or two parts with the GD250 , such as exhaust sensor but for everything else, I personally did not do any detailed comparisons between the MS3 & GD250 as no one was interested , so I did not bother but my memory is faint. It’s just an idea
If not, look for a shop locally that can rebuild starter motors for you on a lower cost until you can get a new one.
Hmm that’s strange.
If its H4 fitting, then yes it must be 55w type (The headlight plastic shell inside will tell you bulb size & watts)
Then while its apart ==> Reach the headlight 3-Pin Plug ==> Get a meter “red probe inside the YELLOW pin” and “black probe on the grey or black wire” (ignore the white wire) ==> You will know if 12V is actually going there, because Yellow wire is high beam
Report back and let us know.
35w bulbs use totally different fittings, so it wouldn’t go inside the headlight and they are for the 5 inch headlight from the early 200os era GV125s
Nowadays hyosung uses 7.6 inch headlight shells with H4 fittings since 2005 for the carb models
I had that before , it turned out that i had to sort out a few parts:
- Coils, Plugs, Caps in tandem
- The ECU wires had some oxidization, so had to clean up carefully and wait 24hrs to dry up
- Injectors just got replace (i couldn’t verify if they were faulty or not, but i just got new ones just to save future breakdowns, so new injectors advised!)
My last worry was the ECU itself but it would sometimes moan and say “Oxygen Sensor” (lambda sensors on pipe) , it would run sweet once i got brand new ones, despite trying a few used sets from other donors. The Daewoo ECU was frustrating to work with, Delphi ECU is a little better but it takes less nonsense! So much as a clutch switch fault ,it refuses to even crank.
though, keep an eye on the “idle speed control unit” , i can’t remember where but the manual mentions it.
Have a look at spark plugs (if they are brand new) , if they are wet = you have also possible stator problem if the coils aren’t sparking properly (they need the stator & ECU to time the sparks)
Glad to hear its alive!!! 😍
The starting solenoid may be shot up. Replacement time.
Though, not uncommon but it happens, investigate the starter motor itself. (Remove from engine, place on floor , get jump leads, put the bike battery on the floor)
I say this , as you may get sparks flying and wear gloves , do it away from the bike itself. You will know if the starter motor is healthy and spinning strong.If you press start on the bike itself , and the engine makes a “big thud” sound at the crank ==> check your sprag clutch (behind the flywheel itself , but i hope not, as its means more work removing the flywheel!)
Good luck and try to take a break so you can enjoy your holidays and return to her with a renewed mind 😉
Hmmm, fully charge the battery (with a bike charger instead of a car version due to excessive current damage)
Get fresh CR8E plugs , connect them to the HT caps , place them on the “unpainted” part of the engine such as a valve cover bolt, see how good the sparks are ? Incase its not sparking strong enough to start ?
Also these stop sparks = Clutch Handlebar Switch (not recommended to bypass), Stand Switch (if bypassed check contacts again) , Neutral Switch stays “Green” on the dashboard
Also , this sounds stupid, do you hear the fuel pump priming when the key turns on?
Using the “Share Link or Get Public Link” option from either: OneDrive, GoogleDrive, Youtube (upload as UNLISTED!) , DailyMotion or other source to upload some video.
Paste it on the forum here, so we can watch what’s going on ? – Ideally stand on the left side of the bike (where the pump is, so the mic can pick up its priming noise)
But , do #1 & #2 before getting to the end of my comment.
Ps. test your stator & tell us the readings (service manual on this forum) , or if its suspicious, the bike won’t start without a good stator, it is the 1st thing it checks.
ECU primes fuel pump (unless its faulty or some other sensor in the bike is faulty , that means spending a lot of time with service manual to test every electric part you can find with a pocket meter) => Start Button is pressed => Solenoid Clicks to spin the starter motor => Stator Gets flywheel speed & pulses back to ECU => ECU, now does it’s magic to try start the bike assuming all sensors connected to it are saying “We’re good to go” or “not responding / poor response = Error Code / ECU shuts off ignition… This is just a simplistic way i can describe the process but the service manual ofcourse has way more detail in how their EFi system works
Push the whole cable outwards , as that switch is slot fitted . So push the cable instead of pulling it.
Switch is one-piece unit , it is the classic style before newer bikes had the switch changed entirely (as did their master cylinders too)
Newer Generation 125 engines & their electrics (RC / P models) , don’t really like bump starts and are VERY hard to start if it feels like parts are not in spec.
~if you try to start the bike with Jump Leads of a RUNNING CAR/VAN = It will never ever start again, bike is too fried.
If you want to use a car or van to start = Remove the battery out of the car / van
or i would recommend to just get a “Motorcycle Charger” (not a car one!) and charge the bike battery , weak batteries make it hard to start too.
I am digressing , but i hope that made sense.
Good, time to replace the starter solenoid relay and the starter motor too. Then the engine should spin faster
In service manual it says if engine spins to slowly , there is not enough cranking to start it properly
Regulator = On this site, look at the shop product pictures, you will see how big it is but owners managed to fit it there. (Bigger is better)
It is the 1st thing i would replace yes, other electrics should be fine. They can be tested later.As for wires, it’s hard to see properly , maybe I will have better answers as i study more pictures of your harness and its plugs , where they are connecting to etc and proper look of wire colours so i don’t make wrong assumptions.
The fuel tank level sensor must not be connected until you see the plug that has 1x Yellow AND 1x black on its white connector.
If there is suspicion on the fuel pump and the owner did anyhing sketchy to the harness to block the pump etc…. (ie. direct feed from tap straight to carb)
Then i would advise later down the line it is better to have a vacuum pump fitted to the bike. We will get there slowly as I can see a lot to do there. Send us a message on ebay if the center stand is needed and I may post everything at once
If the pump is not working, i would not get a new one, nothing good about relying on electric pumps for carb bikes as there will be clones made in China. All my own carb machines have mikuni vacuum pumps , they never bothered me for years on end.
