Midrange lack of power GT125R
- This topic has 28 replies, 4 voices, and was last updated 10 months ago by
.
-
Posts
-
-
Hi all,
I have a 2015 GT125r and it’s a lovely machine. However I am running into a lack of power between 6-9k rpm.
Things I have checked:
Compression shows as 145 on each cylinder, tested hot
New coils from store on here
New Intake O rings from store on here
Carbs upjetted to 90&92.5
New vacuum hoses purchased from store on here
New fuel hoses and filter purchased from store on here
Needle jet adjusted to the richer setting on both slides (bottom groove – I only have 3 Clip settings in my slides)
Slides move freely and don’t hand up anywhere either.
I have eliminated a vacuum leak. Both boots hold vacuum against my hand when cranked and carbs removed.
I can confirm carbs are correctly seated in rubbers and too the airbox.
I tested the resistance of my spark plug caps (they are OEM) and they both read just over 11k of resistance. Could this be what’s causing my midrange lag. Once last 9k RPM I can physically feel the bike pull harder.
I also have what I can only describe as a lumpy idle when the engine is hot. It will tick over at 1500 then will drop to 1k then back upto 1500. If I put the bike in it’s side stand whilst running it will sometimes cut out at idle due to this behaviour.
I don’t have much cash at the moment so can’t afford to randomly throw parts at it so any help would be much appreciated
Thanks in advance everyone.
-
-
—————- I also have what I can only describe as a lumpy idle when the engine is hot. It will tick over at 1500 then will drop to 1k then back upto 1500. If I put the bike in it’s side stand whilst running it will sometimes cut out at idle due to this behaviour. —
An indication on wrong carb-bowl-level …
Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): GT250R-efi
-
-
Was the carb needle on the 1st notch (towards the blunt end?)
Simon is correct , if it goes on the middle slot – can it help ? as that’s OEM. Hence its towards the 3rd tip towards pointy tip, it means you get to “mains” a bit sooner,from stoodstill “pilot” idling.
The reason for the 3rd groove towards the tip is when the slides lift , you get a bit of enrichment since the needle is up 2mm ish out of the carb, so that tends to affect the 4-7k rpm flatness (mid-range) but the 125cc usually revs past 7k pretty quickly on hard throttle when the bike is okay & the main jets simply just take over at this rate.
If the mixtures have been messed with , floats messed with (like Cobra2 says on wrong float heights) = it can throw things off a little bit.
Also when you change gears , do you get any jerk-jerk-jerk behavior then it revs up / rides normally ?
Also can you supply pictures of your plugs so we see what’s happening with the mixture ?
Any intake mods ? any exhaust mods ?
Lots of questions i know but take ya time, more info is good for our heads
// Meditation doesn't mean you have to sit still....
-
Thanks for the replies everyone. I can confirm the needle slides are on the “rich” setting. Before I did this the bike was pretty much unrideable in the mid range.
Only mods are the ones listed above and a bolt on exhaust can. (Bike had this when I purchased it)
I’ve also deleted the AIS. I have made sure that the pipe that used to go to the AIS from the airbox is plugged correctly to avoid any air leaks too.
Bike worked really really well for 3 months then just seemed to start struggling in the midrange and upper midrange. I have never adjusted the floats as I know they need to stay at 7mm with the carb upside down.
I’ll get a picture of my plugs over the weekend. I’m a little busy over the next couple of days but will do it asap. Mixtures haven’t been touched as again I know these are not recommended to be touched by housing themselves.
The reason I mentioned the HT Caps is that I’m sure they are supposed to be under 10k resistance so wondered if this could attribute to it as nothing has changed since the bike was running well. I tested the Caps with them not attached to the HT Lead
-
-
Did you get a chance to take pics of your plugs ?
The OEM Caps are not great as Hyosung doesn’t make them, but some outsourced company called “Golden China” . Using NGK Caps does help a lot and they rarely fail with sparking issues as bad caps can cause weird misfiring issues especially when its hot as its buried deep in the engine heads.
You want the rubber NGK caps similar to the ones on our store. Don’t buy “Plastic NGK Cap” , totally rubbish those ones. (Just like regular CR8E Plugs & LASER plugs are recommended but don’t touch “Iridium IX Blue Box” as they don’t like IX plugs much)
// Meditation doesn't mean you have to sit still....
-
Hi Marcel
I haven’t had chance yet. I’ll try tomorrow. I’m gigging tonight so spent all day prepping for that haha but I’ll get them posted asap.
I do get a misfire when the engine is warm so I will invest in some caps either way. I’m using stock plugs at the moment.
Thanks for the reply matey
-
Stock CR8E plugs will be OK, but swervice manual usually mentions spark plugs all the time as half of fuel / sparking issues as if a carb is good , coils etc but plugs are not, the bike will be jerky since those little things foul easy but we need them little things to get us from A to B (literally)
Laser Plugs + Caps + Coils make a good three-way marriage but lets make sure the bike is good for it, as if the bike is good then you wont change your plugs for a long time (I’ve even had laser plugs on my bikes for 2-4yrs and rarely touch the carbs but it could just be me being OCD lol)
// Meditation doesn't mean you have to sit still....
-
Thanks Marcel. I’ll get some new plugs too as I think it’s due..I still haven’t had chance to pull mine so I can get pics from you but I will do it soon. Just had a whirlwind weekend. Think I may take the carbs off anyway and double check the float heights just to be safe too.
Bad time of year to be working on bikes as I have no garage so have to do it all outside. If it isn’t raining it’s freezing haha
-
I have no garage so have to do it all outside. If it isn’t raining it’s freezing haha
You’re the king of your house , bring the damsel inside and put a rag under the bike and keep the fuel tank outside, carbs out and be wise lol.
It’s gonna snow soon anyways , so we should all have our babies indoors (safely ofcourse, so the fire service doesn’t panic!)
// Meditation doesn't mean you have to sit still....
-
I’d live to bring it in but I can’t get it through our door haha. I keep her covered outside and coated with acf 50 so she should be okay. I’m an all year round rider as she is my daily driver. I always leave her to warm up for 10 mins though..she doesn’t like the cold too much haha
-
Hi sorry it’s been so long. Today I finally changed my spark plugs and caps and the machine instantly feels better. Still have the issues with it cutting out when leaning into the side stand but pretty sure that’s float heights slightly out of whack.
I’ve got pictures of the plugs from the machine as requested and are posted below. Let me know what you think
-
Top
Hi sorry it’s been so long. Today I finally changed my spark plugs and caps and the machine instantly feels better. Still have the issues with it cutting out when leaning into the side stand but pretty sure that’s float heights slightly out of whack. I’ve got pictures of the plugs from the machine as requested and are posted below. Let me know what you think
Top pic is rear plug bottom pic is front plug
-
Front Plug is oily on the threads , i would be looking to check:
- Have the valve stem seals ever been changed ? *(if the valve seal is worn out, it could drip oil in the combustion chamber during revving up = bit of smoke puff on exhaust, it would smell a bit oily, but its a faint hint!) * Check history of that engine if the valves ever got service at all.
Try this bottle “ONLY!” (ignore everything else!)
As it states it is safe for “carbs” and “motorcycles” , Wynns is a trusted brand
https://www.halfords.com/motoring/engine-oils-and-fluids/fuel-and-oil-additives/wynns-lead-substitute-with-fuel-stabiliser-118855.htmlFollow instructions on the box, then generally ride with a half tank of E5 with that product (mix the correct amount! = As half a tank is about 8L ish of E5 fuel) - Check oil level , every 20-50 miles and see if its going down
- Check oil level as above ^ but check if its getting dark & darker quickly (if it was having oil change today)
- Use strictly Motul 7100 – most recommended oil for the 125 Hyosungs and its a high heat oil due to fact our 125s have small oil coolers
- Invest in a Gt250 EFi oil cooler. It will thank you a lot. Do not bother getting chinese coolers , you want the oil pump happy. I’d trust Korea on their coolers this time!
If i am wrong ? Is that wet plug “FUEL” ? — If its wet fuel , then ignore what i said above ^
If it is WET FUEL
- Service the carb and yes check your floats
- Replace the floats , float seats , float needles – So the bike isn’t jamming (while riding) or flooding the cylinder (while riding or overnight standing as it drips out of the carb in to the manifolds then piston chambers)
- Open the “OIL FILLER” cap –> Sniff hard for fuel , if there is fuel smell that is strong , don’t ride it and change the oil.
- Replace the filter , i would mandate this tbh.
While riding === I need to ask?
- Do you hear “popping sounds” in the airbox as you rev up while riding ?
- Does it pull back hard, then slingshot forward ?
- Or does it bog down while riding as revs go up , but only “smooth ride” is during very low speeds ?
I want to ask more but let’s address the top first so we build a proper picture
Let us know everything I just said.
PS. Glad the caps work for you , that’s why we all use them 😉 – Gotta love NGK caps!
// Meditation doesn't mean you have to sit still....
- Have the valve stem seals ever been changed ? *(if the valve seal is worn out, it could drip oil in the combustion chamber during revving up = bit of smoke puff on exhaust, it would smell a bit oily, but its a faint hint!) * Check history of that engine if the valves ever got service at all.
-
Hi Marcel
To be honest the threads on the plug being wet may be due to the fact the sparkplug wasn’t tight when I swapped them out earlier today. I’ll post pics.of the new plugs once my clamps and carb screws arrive as I’ll have to strip her back down then anyway. I’ve put 30 miles in the new plugs and caps today and the bike already feels better. Only bogginess is around 3k rpm to 4k but I’ll be deep cleaning the carbs soon so hopefully that will help.
No pooping in the airbox while revving
And if I gun i have a nice pull throughout the rev range with a slight surge of power just over 9k to 10.5k. I don’t go over that limit but it pulls strongest in that narrow rev range.
I’m using motul 7100 oil. It’s due a change soon so I’ll do that with the carb clean/clamp replacement next week. Oil filter was brand new last oil change, about 1000 miles ago. Good to reuse or would you change it?
-
Hi Marcel To be honest the threads on the plug being wet may be due to the fact the sparkplug wasn’t tight when I swapped them out earlier today. I’ll post pics.of the new plugs once my clamps and carb screws arrive as I’ll have to strip her back down then anyway.
That’s fine fella, keep us posted.
Least she is responding better in meantime , also check your fuel lines aren’t kinked or anything as it is essential for the initial pickup. High revs tend to force more fuel out of narrow lines that are kinked , hence it hasn’t broken down yet but i am only “assuming” since you said it misses at certain revs.
Speaking of “flat spot” , Go to “Tutorials” section of this forum and click “Slide Mod” , it will thank you for it too.
BUT “make sure” it gets a compression test done (search “compression test”) on this forum search box , for old topics as i mentioned how to do it on someone else’s thread.
Also , after doing the slide mod , check the plugs again, clean them hard (Acetone is fine, or carb cleaner or brake cleaner and use a gentle spark plug brush from halfords) ==> Ride again and then give us the final plug pics so we can advise where you are and tell us also if the slide mod made it worse or better, the engine will tell you its mood as you ride.
// Meditation doesn't mean you have to sit still....
-
Hi Marcel.
Sorry for the delay between posts. Long story here so I’ll try to be quick.
You know I emailed you about my uprated coils failing, well the uprated reg/rec has just died too. I’ve just tested the 3 yellow wires from the stator and they are all directly shorted to each other. Less than 1ohm resistance between all 3 phases.
So I think I’ve found out why the new parts were failing. Also explains my poor sparking issues.
Would you need pictures of my flywheel and stator to confirm what unit I need?
I’ve spent so much money in this bike and it’s just decided to blow up all the new parts. I’m not a happy bunny and now looking at another god knows how much to fix her.
-
-
Hi Marcel. Sorry for the delay between posts. Long story here so I’ll try to be quick. You know I emailed you about my uprated coils failing, well the uprated reg/rec has just died too. I’ve just tested the 3 yellow wires from the stator and they are all directly shorted to each other. Less than 1ohm resistance between all 3 phases. So I think I’ve found out why the new parts were failing. Also explains my poor sparking issues. Would you need pictures of my flywheel and stator to confirm what unit I need? I’ve spent so much money in this bike and it’s just decided to blow up all the new parts. I’m not a happy bunny and now looking at another god knows how much to fix her.
Okay I’ve just looked at the specs for the charging coils and the manual says between 0.6-0.9 ohms. So might be In spec then. I’m gonna retest
-
-
Okay double checked and all 3 phases measure 0.8 ohms, so maybe this isn’t my problem.
Voltage of the phases at 4k rpm all sit at 65v AC.
A bit late to rev it to 5k, neighbours won’t be happy.
Any insight would be helpful right now as the bike has eaten 2 coils and and regulator/rectifier that cost me a lot of money. I need to get to the bottom of this
-
-
Do you have the following ….?
- Accessories on the bike that need electrics ?
- What exact battery is on it ? (name and size of it) and how old is it ?
- Has the battery ever had an independent test for free on any local garage or halfords (they use special Yuasa meters for that)
- When riding , does it misfire or jerk forward and back sometimes ? (ignition coils vs cdi = as they do mess with electrics if they go haywire and your reg is still forced to keep sending “regulated” 14 volts on top of charging the battery too)
- How old are the headlights ? Exact bulb and name ? (Generally very old bulbs get more yellow ish and can tax the wires and charging system to light them up) ( I mean new ones already want 55 watts out of the electric system )
Depending on your replies (all i asked) , we will see if it was best you got an even bigger reg rec that’s used on the 650 bikes (see shop) but …… rarely …. As the general global consensus everywhere is that OEM Regs die often more than the proper aftermarket ones (Hyo is power hungry especially later models with more electronics) , hence hyosung changed stators many times across 125 to 650cc models , even the 125cc has had 3 regulator changes by Korea themselves. A good aftermarket reg keeps it going as long as the stator behaves well , and “chinesium” regulators will go on fire faster than Korea’s own regs.
Something on the bike is “overloaded” …. The reg looks like it was having a hard time OR also check the stator OHMS after its warmed up for 10mins , and tell us the resistance (more resistance = more tax on the bike , bikes don’t like being taxed too much) (any bike in general) thats why the stator ohm readings are usually checked ice cold because we know it rises up with heat (heat is the enemy of any electric device on earth)
// Meditation doesn't mean you have to sit still....
-
Hey Marcel
I’ll do a resistance check in the stator tomorrow with the bike fully warmed up.
- Battery is a yuasa ytx 14 BS, not sure on age. Haven’t had it checked either but will get it done at halfords asap
- Headlights are stock bulbs a year old as I replaced them not long after I got the bike
- There are no electrical accessories on the bike at all
- Yes the bike does misfire/jerk occasionally whilst riding, mainly when changing gear, I’ve I pull clutch in, shift up or down and it takes a moment for the bike To respond and can jerk/misfire.
The Regulator/rectifier that blew is already the uprated one from your shop. I’ve had to revert to the OEM one that luckily I kept.
Other things to note. On the uprated regulator the bottom end performance of the bike was much better but top end lacking. Putting the OEM one back on yesterday I noticed a much flatter bottom end but top end power improved.
Also to note. When riding, if I put the headlights on when I’m cruising at say 7k RPM the tacho will do a little jump when switching the lights on. Doesn’t do it all the time but enough to make me question if there’s some voltage leaking somewhere.
Sorry for the essay. I just want to get my machine working properly. It’s my only means of transport, but if it keeps blowing brand new parts I may have to get rid, which I don’t really want to do.
-
Flatter start but gets better as revs rise = That’s the OEM reg that’s already inconsistent. Top end getting better means the reg was doing 15V (I hope not, but not a deal breaker , as that’s the OEM limit) = Though, it could also mean, higher revs forced the bike to get more juice from batter than the OEM reg can keep up?
The upgrade ones should be straight 13.5V from the get go, hence the electronics on your bike have woken up sooner but it won’t try to go beyond 15V. I think i have sold so many worldwide, not just here in UK , the regs i get come from Poland , the distrubitor has been good to me for that and some regs I get are from YSMoto (UK) (YellowSquare Bikes UK) , so they have been good. I’d be annoyed if every reg went on fire!😢 – You might have a voltage leak as you say or something is being taxed elsewhere. Wish i had the motorbike with me in workshop to do more indepth analysis
As for jerking = Our final request is to show us the plugs (Then i will know its fueling or coil issues or stator issue as it does control sparking with the CDI as revs go up and down).
Lights draw 55w , so a weaker reg will dim things a little bit until it catches on. It may look like you will need a 650 reg kit we do, this should be your LAST ever reg. I would be amazed if the 125cc blows it as it is about 3x bigger than the OEM , it’s very big. My 650 customers are happy with it, especially with EFi 2012 ones. We can’t be sending you new regs all the time lol. Spring is here, keep her , bike season is officially here and you know she is a good ride when everything is taken care of.
// Meditation doesn't mean you have to sit still....
-
-
Hi Marcel
Thanks for your replies
Unfortunately the weather has been crap today so not had chance to take her out and warm her up and get the stator resistance readings.
When the weather is a little better I’ll warm her up. Take her for a 10 min ride then I’ll redo to stator check and I’ll remove the plugs and send updated pictures of them. Hopefully in the next day or 2.
In the spring I’ll do a full tear down and check every electrical connection and clean with contact cleaner. She needs some love and a deep clean anyway so I can do them both at the same time.
Here’s a question for you. The loom has diodes in to stop back feeding of voltage. Could one of these have gone bad and there is voltage back feeding somewhere through the system when I turn my lights on causing the tacho Junp and potentially my issues of frying coils and reg/recs?
-
Right, had to nip out to the shop and I’ve noticed another 2 issues.
My indicator relay is buzzing like crazy when indicators are off. Stops buzzing when indicators are on.
And my neutral light is flickering on at low rpm when riding in gear. Goes off when revs rise above 4k.
I think there is deffo voltage leaking through the system somewhere but have no idea where to start.
Unfortunately although the bike is currently warm I can’t get the stator resistance tonight. I’ll follow up with them and plug photos tomorrow. Again sorry for being a pain. I appreciate any and all help
-
If the N-Sensor is faulty, we can send you another one for you to try but i would also get a new oring from the shop for it as there is a camshaft directly behind it with oil, so you don’t want any leaks.
Also, relays = Are the indies OEM or aftermarket ? = If OEM , try to replace both the bulbs (shop) and the actual OEM relay unit (will try find it in workshop)
Defo sounds like something happend with the charging system (reg & stator) that cause electrics to go haywire now., well before you had a chance to upgrade the regs & coils.
Don’t forget even when the bike is OFF (keys out) , the reg is always connected permantently as the red wire goes 3 ways (fuse, battery , loom unit) = if the relay is buzzing without indies being on, that’s gonna cause new battery changes eventually and a very annoyed charging system
Here’s a question for you. The loom has diodes in to stop back feeding of voltage. Could one of these have gone bad and there is voltage back feeding somewhere through the system when I turn my lights on causing the tacho Junp and potentially my issues of frying coils and reg/recs?
Some diodes are simply called “mystery diodes” which Korea doesn’t tell us their actual purpose until we strip the whole loom apart before re-wrapping with fresh black leccy tape. Also Near the “Rear Coil” , there is a relay unit that controls the Neutral sensor , if the green light comes on on dash, the sensor should be working , i believe a voltage overspike (beyond 15v) or too much “amps/current” (stator wanning) would fry it slowly overtime.
Some relays in the harness control lights or the horn beeper. Some older hyosung looms (even 650s) had some at the front that look like relays but actually were called “igniters” for the spark system (like this one…here)
Hints from experience =
If the “RPM gauge” is zig zagging at any point = Coils , Stator , Harness , Battery (Zig Zags can happen when lights turn on, as lights mean extra load is being requested by the bike to stator/reg/ battery to power the lights on top of running the engine)
If the “LCD GLASS” that says the speed you’re doing goes dark, dim, flickers = harness / dodgy part on bike that’s taxing battery / battery or reg itself.
If the “rpm needle” is zig zagging while idling (with lights off) = see above ^
If the “rpm needle” is sweeping slowly up and down = Hunting for fuel , carb , pump , tap, or coils = Plugs may be shot at this point.// Meditation doesn't mean you have to sit still....
-
- You must be logged in to reply to this topic.