Gv125s skipping second gear and vibrating more than usual
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Bike Model = : Gv125s 2021
Hi all,
I’m new to bikes and I went and got myself a gv125s 2021 model about two weeks ago. Everything was amazing with the bike did a few non mechanical changes and all was well.
Until today, I rode into work when I noticed the gear indicator showing third when I was in second, a drop in power/stutter power at the top end of “second” and the engine is causing way more vibration than normal.
I have checked the clutch cable and gear lever and both needed tightening as they were loose and I’ve checked the oil levels and they are also fine. Bought from a dealer in the uk who did a full inspection, service and MOT of the bike before I took possession of it.
I’m hoping anyone might have some advice on what it could be. The only thing i have done differently since getting her is I went on a 86 mile round trip on her rather than my 5 mile daily but that was Saturday and she was fine Sunday 😅.
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If the bike is older than 4,000 miles old, you could take a look at the clutch basket.
If you squeeze the lever in while idling , if it gets quieter = time for a clutch overhaul , sometimes could add to the gear slipping ?
Drain the oil and use Motul 7100 forever (it is possible the dealer used rubbish trade oil from a barrel in workshop, they don’t really play nice for gearboxes long term) – It just an idea.
Then go for a gentle ride , be slower , and see if gears shift through nicely.
Believe it or not, too much chain slack can mess up smooth gear changes and also remove the sprocket cover , see if the sprocket NUT (front engine) is loose or the washer is loose at all ?
If we can do these things first, come back and let us know if it helps.
Idling issue = Go to halfords and get “WYNNS XTREME FORMULA GOLD PETROL” (ignore redex, and ignore everyone else! They are trash)
Put half a tank of fuel inside and put 1/2 bottle of that formula inside that tank ===> Ride until it is 1 bar of fuel left. See if the idling improves (We are “soft cleaning” everything to do with fuel parts , so WYNNS will run through pump, injectors, fuel lines, then gets burnt away inside pistons and O2 sensors pick up last = This should possibly see if fuel clogging was an issue or not.
Idling at 1600-1800 all day is normal and it cannot be adjusted by you. It is ECU control to keep the engine idling
It would be a good idea to get fresh CR8E plugs and stay with them or get LASER ones (good plugs) = DO NOT use “Iridium IX” plugs as Hyosungs hate them.
IX = Blue Box (Avoid)
LASER = Rainbow box (CR8E LASER)
CR8E = Stock plug (yellow box)Now as you finish riding until 1 bar of fuel left ===> Remove the plugs and show us the pictures here, so we can see if the threads have changed colour and how much. Also pictures of the “inside of the plugs” so we can see a trail of what’s going on (too much air, too much fuel, poor sparking (ie. failing coils or NGK caps which the ECU cannot sense) = The ECU will not tell if the coils are failing or the plug caps have issues , you will find out the hard way when the engine stops altogether or starts firing irregular or shaking (power loss when riding too as running on 1 cylinder etc)
Take your time, I said a lot, but i expect some kind of indepth report back from you so we know every step you took and if it is doing better or not.
If it is something stupid like a loose plug or dodgy clutch bearing or 1 snapped clutch plate (happens but rare) , you will tell us and likely someone else will read this thread to avoid ££££££s of labour at garages who don’t understand Hyosungs at all.
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So an update, an embarrassing one but one none the less. Turns out the only issue with the bike is the gear sensor and a loose clutch cable. I got a friend of mine who’s very knowledgable about bikes to take the bike out to ride it and see if the gears all felt right and it was shifting etc.
He came back after riding it and confirmed all is fine other than a loose clutch cable and the gear sensor showing the wrong thing.
What had happened:
The gear indicator showed one gear higher than it should as soon as you get out of first. This caused me to panic about the bike issues and be hyper aware of noises and issues. Then the clutch wasn’t functioning correctly so where I thought the bite was it wasn’t and this caused the power loss as I was preparing to shift gears.
The vibration was caused by me using the gear indicator even though it was wrong. I was in a gear that was too low for the speed I was going but didn’t realise with my fogged mind.
The idle is also normal and sitting around 1600 as per the manual but based on the dial I kept reading 2k as in my haste I was sub consciously rounding up.
The ticking noise is there and it’s around the clutch area of the engine so I will be changing the oil and checking the clutch basket to ensure it’s not rattled loose or what not.
I apologise for wasting your time and Thankyou for the response and all the helpful tips though! I will be looking to do all the things you have suggested anyway as proactive is better than reactive.
I did have another question regarding the location of the gear indicators sensor do you have any idea on where this is located so I can try cleaning the contacts?
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Well done! – Looks like the big panic was over! – Be good to definitely spruce up the clutch and yes proper oil too (Motul 300V or Motul 7100!) – Change oil filter again! Gearboxes LOVE clean oil and you will notice a smoother shift initially.
Gear Sensor = Under the front sprocket, be very very careful as oil will come out of there and it is secure by an O-RING , there is also a spring inside too! So you don’t want the spring to fly out.
Get contact cleaner == clean the Socket going to the harness , incase it got oxidized and some signal loss could happen if there was water invasion.
Use Compressed AIR to blow it clean after using Contact Cleaner (NO WD40 please!🔥)
Get also ACF50 (Halfords) – Spray a tiny amount inside the plug , a very tiny amount. this is every biker’s best friend when it comes to anti rust measures and it is electric safe too.
Good luck!
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