♠️ M77
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hi, so my bike got 1 rear intake hole, 1 front intake hole with rear pump and vacuum fuel tap. how can i apply this method? would appreciate much if could help me.
Hey its OK. Front intake pipe = fuel pump. Rear intake pipe = vacuum tank tap. Only GT250R & GT250 Any 125 owners should follow the original topic at the very top above ^^ Hope that helps.
I have an 08 GT125R with only one hole in both the front, and only one in the rear intake manifold. Would this work for me too? Cheers!
Hey, I don’t see why not 🙂
For optimum performance of the vac system why not do it like this …..
Front Intake ==> T Junction (Plastic or metal) <=== Rear Intake.
The see the 3rd hole of the T Junction? Do this …..
TJunction ==> long hose to rear of bike ===> SECOND JUNCTION
SECOND JUNCTION ==> Feeds Pump and Vacuum Tap.
In other words, you just get yourself 2 junction parts so that front & rear intake both feed the vacuum of the pump and the tap. Since the pump likes it when it gets vacuum from both cylinders of the 125cc
250 doesn’t matter too much since 1 cylinder does enough , but 1 cylinder can also work for 125 , just not optimally in some situation.
Let us know how you get on or if i have confused you in anyway, ask and i will clarify again… 🙂
Hey,
Do you know what caused them to get fried if the indicators are standard hyosung ?Does the relay box say “2x 10w x 3.4” or show us the picture of the box ? I do have a GV relay somwhere that i know works.
However , i am not sure if its 2 pin or 3 pin. Not that it matters too much unless your particular harness is fussy about it 😉 – I have 2 pin relays working on my own GT bikes that are meant for a 3 pin relay , that is also with stock 10w indcators x4
If an ex keeper used 21w bulb on each indicator, that’s easily 84 watts total! compared to 40 watts, god forbid if all of them turn on at the same time, we can see 84w shortly cooking the little relay box
So check the wattages of your bulbs too!
Hey,
I am happy you got your NGK caps. I wanted to respond to this topic and ask a few questions but wow , you already told me on email this morning when i woke up::didn’t notice a loose slider connection to the coil and it was basically working on a single piston,
So looks like you’re already riding away now 🙂
Let us know if you encounter any issues again but i hope not, look after that damsel!
Hey,
I even have an 09 and 11 Registered Aquila myself, they haven’t changed much at all 😉
Regards.
Hi, Fuel pump checked and works fine. Last part will be to fit the K&N filter and bigger jets.
That’s good news! – One less thing to worry about 🙂
See how it goes with the carb, also an excuse for one final major clean, (we can’t clean once can we, sometimes twice or thrice is good!)
Hey,
The as long the pilot jet says it is size 15, it is OK. The pilots are working by the fact you said it idles and revs up like a dream. I would leave the mixture screws at 2.5 turns each and leave it there until i advise when to reduce or increase it based on how it behaves on its upcoming road test ride.
If the pump was opened and there was nothing faulty in it ? Have you connected the pump back to the fuel filter.
The hose that leads to the carb, take it off and see if fuel shoots out and does it flow it or comes out like a trickle drop drop ? If it’s the later, investigate the manifolds are fully sealed and the carb is fully sealed to the manifolds to improve the vacuum system to operate the pump.
Both rear and front manifolds should have nipples to send vacuum to the rear pump as it does need both engine cylinders cranking to draw it open.
Failing that, it may be time to replace the pump. It could be its original one and never investigated in the bike’s life time. They rarely fail , but it does happen & isnt uncommon.
The slide needles both look good to me, can’t see any obvious bending. However, i will say new is better than old. Remember the advise of setting to the 4th grove towards the pointy end or revert back to the 3rd groove , if it behaves lean, 5th groove it is.
The needles take full effect when the bike revs go up and you’re riding as its part of “main jet” fuel metering.
I am glad the bike is running at least, so i think our last stop is the diagnosis of the fuel pump and vacuum system. I got your email , i’ll reply to that one too shortly!
Hey Mike,
If you can see the filter filling up, that’s good. That means the TAP is on from the tank area.
Next, take the fuel hose OFF the carb and point it to a bucket , then see if the fuel pump is shooting fuel out ? The pump is the one that sits near the battery ofcourse.
- This will check if there is enough vacuum to open the pump so it can do its job, it works in a pulsating nature of the engine intake cycle strokes , and it needs fuel flowing through it to work. Henceforward check the tank tap is working first by observing if you see the fuel flowing through the filter.
- Consider the hoses not to be kinked, the bike does also like gravity assist, so consider how the neat the lines are routed.
If the pump is good to go, then ofcourse the carb needs addressing again…
- Take the pilots out, and look in the sky. If you can’t see through them, there is debris inside you will need to clean them harder. It is these jets that will cause the bike to act moody and cut off.
- Mixture settings all good from my last advise ?
- Get a clean hose..connect it to the carb, consider your mouth please as i rarely advise this redneck method of doing something but lift 1 float, blow through the hose , and let go of the float. If you sense air is flowing through with ease.
Repeat with another float. Then you know your fuel valves do open/close based on the float raising or resting on the needle.
If the slide needle is on the 3rd grove pointing towards the tip, place it on the 4th groove facing the tip, that lifts the fuel up sooner as bike revs increase.
Check the slide cap isn’t leaking any air by ensuring the slide caps were flat and screwed in well, as if there is a chance of air leak, the slides won’t lift efficiently , thus the bike dies when revs increase.
I haven’t address the air intake system (orings, manifolds, airbox) as you have said you installed them as religious as you could.
I hope after this you can finally have results and test ride the bike yourself to see how it is behaving.
if the rpm needle drops fast ….and the revs stay at 1700 rpm (ideal) hot, the bike is OK.
if the rpm needle drops really slowly … you either have a pilot jet clogged that’s hunting fuel or there is an unknown air leak.Hi Mike,
Ignore the fact someone used 7.2mm (extra .2mm is extreme!), I just used their picture, it is too dark at the moment for me to fetch out a carb and take a picture, please excuse me for that.
- Just make sure its 7.00mm like this photo shows and you should be good to go…
- Also, lift the float, and let it go, you should hear the valves under it bounce a tiny bit, only a tiny bit! Then the spring inside the valve isn’t totally dead. It makes for awkward fueling situations for the float if the valves are dead.
Hope this info helps.
Top Yoke Decal – If i know a UK maker i will let you know or i may just do it because someone from the US actually wants to do it but i told him i’ll think about it. It was going to be a new shop item on a limited run to see how they fair up in popularity.
The coils , i meant checking their primary resistance and also secondary resistance , i mentioned a few times in other threads on how to diagnose certain electric parts with a multi meter , if you browse around, if not i can always dig out a topic and link you directly to it.
And you’re welcome !
Patiently following this 🙂
If you will , try to also reinforce the internals of the motor by putting beefier parts though, more power more responsibility 😉
Things like better bearings, new cam chain , clutch pack, sparing no expensive to motul oil, and what not.
Thank you your a star I’ll give it a go tomorrow also the gt125r has 5 gears not 6 is this right?
Correct even 250’s have 5 gears , they don’t need 6 gears for what they are to be fair. Although 6th be a little nice overdrive haha.
It took 6th gear for a Yammy YZFR125 to hit the 80s , hyo does that in 5th.
Korea did not reveal the turns to discourage owners tampering with them , and due to the fact 125cc and 250cc , GV and GT, have slightly different turns from each other based on what model the bike is and the jettings used.
So your profile says GT125R (a carb with a jet pump attached to the rear float bowl), use around 2 and 1 quarter to 3 full turns max. Rear being slightly richer as it’s the hottest cylinder.
1/8 of a turn does make a difference, so i would encourage a carb ultrasonic cleaner and dead-on adjusted clearances & lastly a religously clean intake system that’s also leak-free including how far the airbox swallows the carb, and intake manifold orings changed.
You will find that if any of the above ^ is not done, the mixture messing will be a nightmare to get it spot on.
Sometimes tools to anaylize the heat of the exhaust pipes also helps , even as much as reading the air/fuel ratio that’s coming out of the tail pipe. Clean & new spark plugs will be a good hint after a short run.
Show us the plugs when done. (though , it can be expected to go through 1 or 2 plugs , as per typical “plug chopping” process)
I hope this reply helped.
Sorry I’ve been away at inlaws this weekend, so i stand corrected that you did not fit it yourself the original 428s. As i will quote your exact reply:
the 13 front and 49 rear was on from when i bought it…..theres nothing in the side panniers the chain was a gold one the type with rubber seals…. its had a engine swap done by oiley bikers top speed before was 62mph using gps at aound 1100rpm the bike has done 19.488 km its had new ngk spark plugs new ngk uprated caps new ht leads new CG125 coils carbs are standard i use castrol power one 10w 40 oil plus run orangey brown. v power fuelto be honest with you i dident think it had adjustable valve clearences the bikes speedo has indicated 70 before but in reality using a gps app it was doing 65mphUsing the gearing commander (it’s on google) so you can play with the settings if you like) it’s a decent source as it is on par. I played with various 428 sprocket settings on a GV125, the 13T and 49T defo drops the mph for sure, it’s not factory set up.
I do own aquilas and GTs , i know the speedos are out, so the speeds i mention when selling chain sets are what it says on the dash, i can’t try just one bike , i need several donors with varying engine mileages , some modded bikes, some stock and i have people who are test dummies to help me and i send the kits before i go retail, i can’t take back what i say online, i’ve way too many witnesses now (which is a good thing), 10% has to be removed when GPS is used. No speedo made by hyo i’ve known so far is ever the same as GPS. Even most cars are like this, sometimes 10-15% is removed from any speed to actually slow down people (even though they think they are truly driving 70 in motorways) but no they drive at 80mph on the dash so it’s 72ish on GPS, are they taking a risk with smart-camera motorways ever increasing, yes they are but its what i see everyday.
Don’t worry too much about the chain set for now, we’re going back to the engine internals (cams, clearances, clutch basket, compression, etc) && (plus whatever else is attached to it, be it fueling or electrical things to make it come to life)
If one has a digital hyosung dash, and it says 33, going down the estate, the light poles in the street will have a matrix display saying “Your Speed xxxx” – 33 on dash is always 30 by the matrix display in the street = that’s 10% removed from the dash. 44indicated is 40. I can see why 80 will drop to 70 gps as any speed is always factored in around 10%. Common figure , some dashes are less out (5%) , some will be 15% out.
The revs is the main concern on a small cc bike, we want it screaming less at the “same” speed it did before a change of modification (ie. chain set) , the valves on hyosungs don’t like staying at 13k revs for long. The valves start floating at 12k revs. All GV125 engines peak their power at 10-11.5k revs.
Please take a look at the service manual below which another member has kindly posted on social media, as you’re on it already, if it helps. I know trawling through the forum has all kinds of books, but i’ll organize that much sooner with another site design change.
Link to manual here
https://www.facebook.com/groups/345623961212/permalink/10156911795301213it is specifically for your bike, so it has so much detail. The troubleshooting section at the end will back up the “clearances” being mentioned multiple times (even if engine idles fine), the challenge now is to beat everything the engineers have said in the book. Trust them than any of us here , they made the motors 🙂 . You’re a mechanic yourself fella so the book’s instructions will be familar to you in some pages read, if not, a local garage can do what the book says and don’t pay them until it is so. (Some garages are just cowboys, sorry to say, they really are, so i’d watch them!)
If the manual has something missing, tell me i’ll upload it again directly to this site.
Have a great weekend ❤
PS. I really do need to start making more tutorials of engine jobs unless Korea’s english is perfectly fine , I can try to break things down to layman terms.
Like this tutorial here on clutch ( i do need to update it anyway)
https://hyoriders.club/forums/topic/tutorial-hyosung-gv-gt-125-250-clutch-plates-replacementI have tried to advise the customer in a few occassions that it will be easier if the bike had clearances done and a deep clutch inspection. I wanted to know every nook and cranny of the bike including seeing the plugs “with my own eyes” , so i can see any potentioal bottlenecks , and i would have advised some mods to do free.
He has already done 1 carb mod which is altering his slide needle to improve the 4-7k range. (mid range,) that’s well and good. he would pass a stock GV, just a little bit side to side.
He said it’s had an engine swap and mileage is beyond 10k miles. It needs clearances doing. I’ve advised the valves really do matter when it comes to top end performance.
I’ve advised it doesn’t always need to be modifications but it can help sometimes on the “lower end” so it has a bit more oomph to start off before it runs out of puff at the top gear
He has not told me what the maximum speed was in 5th gear and what rev range it was on, this is with a 520.
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See the screenshot of another customer below ::
This aquila is brand new and he is the only owner and he was my test dummy when helping me choose the correct sprockets during the time i was doing 520 kits for GV125 aquilas. No one was doing 520s for the GV’s years ago after all, the UK isn’t the only country i send chains to. There is many GV owners on here from spain and other eu countries where the 125cc exist, they seem to ride a lot more than we do! I hope they prove me wrong!
Make of this image below of what you will , my other client has not done any mods , he is an elder man with full bike license rides a pan big cc tourer. He kept the Aquila as a winter hack. The only mod so far was the chain from this shop.
is his speedo out? GPS either way is in the 70’s and he is in 4th gear trying to get past a car that was moving too slow on a 70mph road.
This is a dual carriage way, look at the horizon, the road is FLAT (mostly) , there is not much downhill here, if anything, the road inclines up a little bit.
Moving on, i advised that if the clearances get sorted out, she will be happier.
I would not send Roy a 35T sprocket because his engine isnt ready for that, I can go as low as 30T (which 30T is unachievable on a 125cc no matter how tuned, 30T has a theotrical max speed of 100 mph, it just won’t happen)
So i customized his gearing to peak at 90 and while that is well and good, it dropped his revs down to about 1,000 rpm less which is intended, as the aquila should scream less.
If i drop the revs too much, it won’t accelerate as good, i had to make a balance, the UK has hills and what not, i do not know which rides he uses.I would gladly send him a 30T sprocket, he will still moan the bike is not doing 90mph. Will it be the 520’s fault?
No, he hasn’t even maxxed out the chain kit I have sent him yet, which suggests a garage must check his clutch and clearances. He says it’s good. Korea will say the plates should be a certain thickness and a spring should be this way and that way , from the service manual to suggest if the clutch is “good” or “wanning , but rideable” , mind you the engine is 10k+ old. It will not be the same as a bike that’s 1,000 miles run in.
Clearances matter. We could spend £400 trying to go fast with mods, but clearances will draw the motor back if its hot and valves close/open too soon, hence clearances to be done. In the same time, his mechanic will do a COMPRESSION test.
150 psi is awesome (example) , 120 is OK but at the limit. 150 psi with engine that’s got clearances of 0.10 & 0.20 dead on will be faster in general (modded or not)Then henceforward, it’s much easier for the 520 chain set to do justice.
Now then, the GV 520 kits are meant for 2 things (longevity) as i know aquila riders like to go on long stretches and carry things (panniers!) . A skinny 428 will wear out much sooner. I can attest to the fact the hyosung bikes i fix in my own workshop i always change to stronger chains , & 2 clients have had issues that almost caused them an accident. Is it Korea’s fault ? No , they ship with Oring chains standard, but after that cheaper 428 chains are fitted by garages once the bike comes of age.
Next, KRMotors and any owner that’s bought a brand new aquila will quickly realize the top speed is 70 ish screaming at 13k revs. Is that healthy? No.
It’s all well and good to drop teeth on a 428, but you loose either top end or acceleration as dropping teeth is more dramatic than a 520 (520 cog teeth are more spaced out, if you want to be scientic, a 14T 520 will have a circumferance of 10cm and a 428 14T will be 7cm (this is an example). Rotation size and spinning size mass matters if we are to get scientific, not just the “teeth” count. Gear ratio matters in this case.He said he has already put a 49T on the 428 which the aquila uses 46 or 48T factory. I was wondering why it won’t hit 70 in the first place. It’s got a 49T, he needed to get lower, which i did on the 520.
Now henceforward he hasn’t maxed out 5th gear at 13k revs to tell us what speed it was on 520. He already knows the bike screams less.
GV = To scream less, and more durability when carrying panniers or going extended tours (hence “Cruiser”) , it’s never going to be a drag racer. 80 is possible because the engine is “designed to do so”
GTR = uses the same GV engine and its factory “82-88mph” = GT520 kits (more accel in general, just a little bit, no point me focusing on top end as it already does 80+ factory and ofcourse chain longevity over a skinny 428)
GT= Same engine as the GV = 80+, though its naked so it will have some wind drag slighly.
GTR is the fastest of them all , GV was purposefully dropped to 70 by Koreans by means of certain restrictions and weird gearing , so bike is already screaming.
80+ is not impossible , you want less revs = happier valves, you ain’t racing on a drag strip but you want to be able to go 70 in 4th gear and 5th gear now becomes your overdrive.
Whereas on a stock GV you’re already on 5th trying to scream to 70.
I say all this with love please ❤ , but had i known more in depth of the motor , i would have advised a little overhaul job with your mechanics professionally and they will follow the “service” manual. I will then talk to them what the bike needs to meet the client’s desires, i can get super technical with them. Once its in spec, then pimps happen after.
If in any doubt, please ignore this website, research the top end speed , and watch youtube videos of riders attempting the national speed on a “stock” GV and look at their rev counters.
If in any doubt again, please trust the Korean engineers when they mention what to do when bike has speed issues in troubleshooting section of their service manual. Also follow what they say to the T including clearances, carb, fueling, their service manual has a lot of detail and a LOT of checks happen for every part inside the bike including measuring things to see if they are at their limits or not, and beat their limits.
You will be much happier, don’t spend on any more mods, just do what the service manual says every page, she is past 10k after all and so will she show her mood after wards, even if its a little bit better, it’s better than nothing or can leave her alone and enjoy for her what she is & allow the mechanics to sort it themselves , just don’t use cowboy garages or you will waste money again ❤
I notice the gt125s can come with either step type rear shock or threaded type not sure if they are different but anyway is the suspension on these absolutely shocking or is mine just in dying need of a rebuild?
QuoteYou can use the GT650 shock as its more firm and it does raise up the bike a little bit.
The old gen shocks are much better wearing because i like the step_mountain clicking adjustment , than screwing type. Both shocks do need religious greasing to keep rust at bay though and their legs painted. New shape shocks found on newer bikes suffer from the “warp bending” effect on the legs when rider is always on the bike everyday , eventually it sways . However, the leg metal plate that a bolt slots through can be taken off and a fabricator can copy it easily and use much stronger steel.
Various bandit shocks are known to fit the hyos but they are without some modifications in some cases. Sometimes the hyo’s under tray needs cutting/trimming around for clearances etc. I never bothered with it since i am still using an old gen shock 40k miles later, i just put it on the stiffest setting and that also includes carrying luggage or a pillion sometimes.
However it does remind me i should probably spend this winter and see if i can mess about with my donor aquilas as they have double shocks which are old but surprisingly holding up fine!
I’ve copied your topic to the other one for you, so i’ve locked this one 🙂
Hey,
Are the plugs “IX” or “IA (Real LASER)” – I say this because Hyosung 125s don’t enjoy IX plugs for that long. It’s the LASER or stock CR8E are what they like most.Have you had a chance to browse around the shop section as what’s on there is what many of the registered folk on here use , and to the extremes they do eventually see 90 indicated on the dash.
Humbly speaking as a wizard, it is a little overkill to try to mess with the valve heads or boring the cylinders out. However there is no aftermarket oversized pistons for the vtwin , as i don’t think the crank wants to deal with a big bore kit (like you see on the Yammy 125s). It’s actually not a bad engine to be fair as it is, it’s only the weight of the bike that lets it down on the initial take off but it will defo hold down long stretches on the M or A roads better than punny little single cylinder 125s. Believe i’ve pushed the donor 125 all the way up & down the country on the M1 & M62 , i was pretty surprised coming from a guy who only had a ZZR400 that did 120 at best! and ofcourse the GS500 i recently sold.
90 is good for the hyo. However, i do like your bravery to go to the dark side , not many of us actually hone the cylinders or mess with the valve heads.
You may get yourself custom made titanium valve springs for the cams. No aftermarket folk do this for Hyosung 125s, so totally a custom job here.2 pipes (rear and front) joining to 1 pipe to the end can, seems to pull best on 125s with a long exhaust can that has a baffle hole of the size of 10p. I tried a few configurations before. If doing dual exhausts, that will look really good i won’t lie , just be sure the cans are full size with a small baffle hole so it isn’t loosing out too much puff out there. It’s not a 2 stroke , but you’ll be surprised the 4t pulls more with a baffle in than out.
I did make 2 tutorials on the site for carb jetting and the slide mod which you can check out as you browse deeper in the forum
Thank you Marcel. I have ordered parts according to your first recommendations below and will see how this goes before going further
No problem fella.
