Carburetor GV 125 Year 2012

[Max]

Hi Guys,

My Name is Max and I´m proud ower of a GV 125 classic KM4MF53A.

I need information about the settings of the carb. Especially the adjustment of the height of the float chamber.

I have adjustet it to 17mm because I only have the service manuel from the previous model. I Can tell you that it didnt worked well.

The slider with menbrane YK8844 is a little sluggish, means it doesn´t slide very well up and down and sometimes it is a little stuck. Any tipps?

Also it would be interesting which lengh the spring of the above mentioned slider should have.

Also I have difficulty loosening some screws, do you have any tips?

Maybe it is even easier to replace the whole carb, are there any opportunities to pay less than 630 Euro?

The matching workshop manual would be a blessing.

 

Thanks and sorry for the bunch of questions 😆

regards Max from Germany

 

[Alan McLean]

Hi Max and welcome. The float hight should be 7mm (not 17 as per the manual) this is measured with the carb carb body turned up and the float is just resting on the needle valve, measurement is taken from the top of the carb body to the top of the float. As regards the slider sticking just remove it and clean the slider and carb body with carb cleaner or a little WD40, do not use anything abrasive on the slider or the body of the carb, it’s probably just some old fuel residue causing the problem and it’s just as well to clean both while you are at it. As you will be removing the sliders it would be a good opportunity to do the slider needle adjustment, if you type “tutorials” into the search bar there is a tutorial there to show how it’s do, it’s a simple job but worth doing. As regards the springs I would leave them as standard. Removing the carb screw’s is always an issue (poor quality soft material) first make sure you are using a driver with the correct size JIS tip, if that fails a small vice grips usually does it, I would then strongly advice going to the “shop” on this site and ordering a full set of s/s carb screws from Marcel and you will never have the problem again.

Hope this helps, Alan.

 

 

[Max]

Hi Alan,

Thank you so much for this quality advice! I will do it the way you described.

In this case I have to contact Marcel whether he makes shipping to Germany😄

All the best and have a great weekend.

[Alan McLean]

No problem Max, hope it works for you. I do believe Marcel would ship to Germany as I’m in Spain and he has sent items to me 👍

[Max]

Very good news. Do you have any tips for removing the carburetor? I am worried about the connection to the cylinder..

[Alan McLean]

The most difficult part is removing the airbox, it can be very frustrating but with time and patience it can be done, I have done it a couple of times and it gets easier each time.

First remove the seat and fuel tank (have you removed the tank before?) then unbolt the oil cooler and pull it towards the front wheel no need to disconnect the pipes, remove the air filter and housing and plastics around the air intake, unbolt the bracket on the left-hand side of the bike holding the two coils just let this hang down out of the way, disconnect vacuum pipes etc. from the airbox.

May be a good time to take a break now 😉

Now comes the difficult part, loosen the two clamp’s holding the airbox to the top of the carb’s, there is also a screw on the right side holding the airbox to the frame, remove this, gently pull the airbox up off the carb’s sometimes the wiring loom running running along between the airbox and frame can restrict movement so just pull the loom to one side. When the rubber couplings are clear of the carb’s push the airbox forward towards the front wheel, it will only move a couple of centimetres, now push the airbox to the right side of the bike (I find it easier getting it out this side) it will take a lot of pushing and moving the airbox back and forward to get it out so just be careful not to put too much pressure on the carb’s themselves during this process as this is when the manifolds can be damaged, I found it useful to loosen the clamp’s on the bottom of the carb’s to the manifolds this can give you a little more movement and believe me you need all the space you can get with this job. Hopefully after some time (and probably some bad language 😄) you will have the airbox out.👍

Removing the carb’s themselves is now the easy part, disconnect the throttle cable, choke cable, fuel pipe and vacuum pipes, loosen off the manifold clamp’s fully and gently lift off the carb’s. If I have forgotten anything I apologize but I’m sure you will figure it out.

Good Luck.

p.s Going back on is just reversal of above but I’m afraid no easier 😔

 

[Max]

Hi Alan,

Thanks a lot for your quality advice.

Regarding the slider needle adjustment, I havent done any modifications. Means Its the original Airfilter, normal spark plugs (new), and the two original main jets.

Does it even make sense for me, under this circumstances, to adjust slider needle?

Or would you say, I should change spark plugs, Airfilter, main jet and then do the needle adjustment?

Just for information:

I had a problem with reaching the high speed, the bike goes hardly up to 90 kph. Before I failed with the float hight adjustment. I checked the valves, the fuel filter, the fuel pump and the spark plugs (the distance was to big, that why I got new ones, bit couldnt try If that was the reason for no high speed because of the float hight fail)

Again thanks and have a nice sunday

Hasta Luego Amigo

Max

 

[Alan McLean]

Hi Max, The slider needle adjustment allows the carb’s run a little richer than the factory setup, I did it on my bike prior to changing the two main jets as mine had a flat spot around 5k rpm, it solved that problem for me. It’s probably worth trying as it’s a simple modification and if you’re not happy with the results you can easily return it back to factory settings.

The best way to judge your fueling is ok is by the colour of your spark plugs, so you could check the condition of them prior to doing the mod and then checking them after the mod (clean the spark plugs before riding it again after the mod) once you have ridden it for a while.

Alan.

[♠️ M77]

Just to add also,

How to remove airbox from GV125 an easier way….

• Loosen bolts for rear intake pipe.
• loosen clamps for intake pipe front and rear.
• Now, remove rear intake pipe”very gentle” and slowly  from the bike.
• Measure bolts for intake pipe  (eg. M6 x 20 for example, and get stainess steel please)
• Now loosen and slowly remove front intake pipe from under the carb   (slide them out nicely)

Step 2….
Loosen airbox bolt from the FRAME (1x bolt holds airbox to frame.)

Voila, the carb and air box have come out easy.

 

To fit everything back ,  do the steps above ^ in reverse.

This method protects manifolds and puts them away safely and you can take the airbox with carb together away from bike too next.

Caution = If you remove intake pipe , please change “manifold ORING” everytime, as old ones get flat or old after a while and air leaks will happen.

Caution = Get big masking tape, and hide engine holes , you don’t want to accidently drop bolts or metal parts inside engine holes and valves will seize when you start.  Make sure engine surface is very smooth and clean before fitting manifolds again.

Everything else,  follow Alan above ^ , i agree with what he has said so far 👍
This link is the slide mod is below

[Tutorial] How to adjust Carb Slide Needle (Tuning) – Hyosung GV & GT 125/250

[Alan McLean]

♠️ M77 wrote:

Just to add also, How to remove airbox from GV125 an easier way….

• Loosen bolts for rear intake pipe.
• loosen clamps for intake pipe front and rear.
• Now, remove rear intake pipe”very gentle” and slowly from the bike.
• Measure bolts for intake pipe (eg. M6 x 20 for example, and get stainess steel please)
• Now loosen and slowly remove front intake pipe from under the carb (slide them out nicely)

Step 2…. Loosen airbox bolt from the FRAME (1x bolt holds airbox to frame.) Voila, the carb and air box have come out easy. To fit everything back , do the steps above ^ in reverse. This method protects manifolds and puts them away safely and you can take the airbox with carb together away from bike too next. Caution = If you remove intake pipe , please change “manifold ORING” everytime, as old ones get flat or old after a while and air leaks will happen. Caution = Get big masking tape, and hide engine holes , you don’t want to accidently drop bolts or metal parts inside engine holes and valves will seize when you start. Make sure engine surface is very smooth and clean before fitting manifolds again. Everything else, follow Alan above ^ , i agree with what he has said so far 👍 This link is the slide mod is below

[Tutorial] How to adjust Carb Slide Needle (Tuning) – Hyosung GV & GT 125/250

Quote

I will have to try that method myself Marcel the next time I have to remove the carb. 👍

[Max]

That method of Marcel works very well. Thanks a lot for this tipp!

 

I noticed that the slider needles are set differently and also the airscrew on the rear cylinder was only unscrewed 1 1/2 turns. Furthermore, the springs for the diaphragms have slightly different lengths.

If I now adjust the slider needles according to the forum. How far must the airsrew be unscrewed ? And both front and rear same ?

Do I still have to match the carburetors so that they run in step? If so, how can I do that without special equipment?

Thanks and regards Max

 

[Max]

Update:

in my carb were wrong pilots and main jets. Pilot 17.5 and main 82.5.

Where can I get new main jets?? And shall I go for 90, 90 front and rear or 87.5 + 87.5 like original?

I enclose you some pictures

Diaphgram seems ok right?

What are the two screws on the float chamber covers for, do they belong screwed all the way in?

 

[Max]

okey actually it seems like it´s a different carb and the 82,5 is the standard main jet 😮

[Alan McLean]

Hi Max, not sure what you mean by different carb’s, have they been replaced at some stage?

As regards the fuel mixture screw all I can tell you what mine are set at (factory setting) Front 2 1/4 turns out and rear 2 1/2 turns out. They do recommend that you don’t alter the factory settings on these but if yours has been tampered with you could try the settings above.

Marcel is the best one to ask as regards the main jets, he supplied me with larger main jets front and rear (rear been larger than front) I did not change the pilot jets, my original main jets were 8.25 front and year. The theory behind having a larger main jet on the rear carb is to aid cooling of the rear cylinder, but as I said Marcel is the guru on these matters.

The two screws on the the float bowls is just a drainage screw so should be screwed closed, not too tight.

Alan.

[Max]

Hi Alan,

Thanks for your reply.

Seems like we have the same Carb, which year is your bike from?
I had only wondered, because I expected 87.5 Jets and not 82.5. I think your settings will only work if I also update my main jets.
Which sizes do you use right now?
And do you use these bigger main jets with the same slider needles?
Are there anymore new parts in your carb and how fast is your bike going with these settings?

I can’t wait to get back on the road 😀

Best regards / Saludos
Max

 

[♠️ M77]

Hey Max,
Send me an email if you need Pilot Jets  (Size 15 is oem for all 125 twins, but sometimes you will find  17.5 added by other owners and makes bike hard to start)
I will not ship your parts until you let me know first please.
I also have some “main jets” too.

For GV125 only this is the optimal settings:
Size 15 Pilot Jets =  2.5 turns out mixtures , both front and rear.
Size 90 & 92.5 is the max jetting and recommended.
Slide Needles = Factory is 3 grooves.   3rd groove towards pointy tip is good.
If you have 5 grooves = 3 to 5 groove towards the pointy tip is good, but check spark plugs and fine tune it.  Maybe they like 3 or 4,  because 5 is very rich.

Size 87.5 & 90 is OK too as long as bike uses standard factory exhaust and do no modify air filters (GV’s don’t like pod filters ever.)

Do not worry too much about air because GV250 also uses the same air filter and air box, it will flow enough air for 250 & 125cc.  Just make sure filter is new because they get clogged faster than GT125s   (GTs use 650cc air filter and are able to filter air for much longer before bike starts to feel like its on a leash & slower/sluggish).  Around every 5K is a good time to check GV air filters to keep air flow optimal.

All GT125 have 87.5 and 90 because i work with a lot of hyosung bikes now ,everytime i do some upgrades ,i always find 87.5 front and 90 rear.   82.5 on a GV is too small but it is probably to slow it down  (restriction?) but most motorcycle makers these days used to put smaller main jets to try meet EURO laws but there is a problem, they will be leaner in top gear (and thus bike gets much hotter), so its not good for piston rings in the long term.

I hope i have made sense ,  good spark plugs will help burn that extra fuel , but we will deal with electrics another time 😉 , lets fix the carb first.

[Alan McLean]

Hi Max, my GV is 2010, when I got it she was running very poorly so after checking all the electrical side of things I decided to take the carb’s off to clean that’s when I checked the number of turns on the fuel screw so those were the factory settings before I did anything.

I adjusted the needle/slider mode before I changed the main jets, it did cure the problem I had with a flat spot around 5k rpm.

I then decided to go with the larger main jets as per Marcel’s suggestions 90 front 92.5 rear with the same needles, this made the biggest difference, where I live is quite hilly and the bike would struggle but after changing the main jets it was a completely different bike.

I will probably adjust the needles just to tweak it, I still feel there is a bit more to be had from her but happy the way she is performing at present. Just for example I have been away for the last four months and when I came back the bike started on the second push of the button.

I think the next best mod I can do is the 520 chain and sprocket kit from Marcel from all I have read it’s a big improvement over stock, and as I said it’s quite hilly where I live so the 520 kit would certainly help.

 

[Max]

Hi Guys,

Everthing is build together! With slider needles both in 3 of 5 and air screws 2.5 out and 90 plus 92.5 main jets. New Air filter is build in too as well as sparkplugs.

My bike still cant rev over 7 to 8 thousand rpm. and about 70 to 80 kmh.

Im really sad surprised right now.

Any Tipps??

Max

 

[♠️ M77]

Max wrote:

80 kmh

That is like the imfamous “can’t get past 60 mph” issue here in UK too.

I would check the following or replace;

• Ignition coil , sometimes sparks will come out of the wires (coil arcing) , or HT cap is faulty
  These 2 parts are common failing OEM parts.
• Spark Plugs are breaking down.  (Dying)
• The Carb Slides are sticky  (dirt again)
• Regulator faulty under heavy load (common), oem regulators are not great.
• Main Jets may be clogged again
  (sometimes we clean carbs 2x before we are fully satisfied, so be ready to clean carb 2-3x time before engine is happy with result)
• check intake pipes are not leaking air (spray carb cleaner near them)
• spray air boxes  top of carb and air filter box  (2 boxes, for any leaks near the joints)

 

[Max]

Hello Marcel,

Thank you very much for your great advice.
I checked the cables of the spark plugs and found that I get electric shocks through the cable. Especially at the front cylinder it was strong. At the same time I could not see but hear the spark on the rear cylinder.
I also made a video of the spark, you can watch it here. https://youtu.be/pfjwQTfNMLQ

I am curious what is your assessment of this.
Thanks again for your really great support.

[♠️ M77]

Hello,
If you are checking for sparks, you should also rest the spark plug on the the cylinder head bolt  (or any part of the frame that is not painted) so that you get a good ground connection.  Then see if the sparks are strong or poor when cranking the bike.

If you suspect the sparks are coming out of the cables when engine is in idle , you should replace the coil and HT cap.

Did you also do other checks i said above ^ ?

[Max]

Hi Marcel,

In this case I have done it wrong, but I definetly got some electric shocks through the cables. I will check die sparks as you explained, this afternoon.

[Max]

Here is the update:

60 mph problem.. at least you habe heard of it haha 😅

Still electroshocks in my hand from the wire of the front ignition coil.

How can I test if the regulator works as it should?

Thanks and best regards

Max

[♠️ M77]

It could be advised to replace the front ignition or both of them  (and keep one as backup).

Also when bike is running this is OEM values for charging system on your battery

• Idle 1800 rpm hot =  14v
• 5,000 revs  = 14.8V  (15v max)

Regulator that’s producing 13.x or 12.x volts in any revs is not good.  And to be honest , a lot of owners worldwide replace regulators for better ones because the Korea ones are not great. Hyosung does not make them but they ask another Korea company to make stators and regulators for them. But i digress sorry , have a good session testing it and let us know.

Also, maybe get a USPRO Compression Tester from Amazon and check your compression for your pistons , after the engine is about 20 mins hot.

Sorry for the delayed reply.  You got this 🙂

[Alan McLean]

Hi Max, as Marcel say’s check the charging rate coming from the regulator rectifier, you can also use this method https://youtu.be/-Rqh1PXD5H4 another tell tale sign is to check the underside of the regulator they tend to blow diodes and this can be seen on the underside of the regulator.

I would also recommend changing both coils and plug cap’s as Marcel suggested.

Best of luck.😔

 

[Max]

Hi Guys,

huge thanks for your advice.

I will check compression and reg on friday. How much bar should the compression test give?

Thanks for your support, i can’t wait to ride the bike. 😎

[Max]

Hi Guys little update

sparkplugcaps replaced, no change 🙁

Both cylinders have compression over 12 bar so engine is fine.

Maybe Cdi is defect?

what do you think?

Now I will take the carb for ultrasonic bath. And maybe replace cdi.

Regulator looks normal and I cant imagine this thing to cause my trouble with the high end power?

[♠️ M77]

12 Bar is very good, that is like 175 PSI for a 125cc Hyosung twin. So engine is OK.

For the engine, now if the top speed is poor, i would definitely check with service manual these 2 because it is also true;

• Valve Clearances
  Get a feeler gauge and follow instructions and see if any valve is out of spec?
  Tight valves = hard starting / overheating / poor speed.
  Loose valves = noisy / poor speed / dangerous if too loose, it will annoy the chain tensioner.
• Clutch Plates
  Get Venier Calipers and measure clutch springs and measure plate thickness vs manual oem limits.
  Bad clutch = bad speeds.
  Beautiful big (heavy!) girls the Korean bikes are but they like to eat clutch and brakes!

So if engine is sorted, next step try these tips:

– Show us which caps did you get ? If they are NGK CAPS, then no problem, ignore this message.

– Next tip, replace ignition coils.  (Better ones , like these we have )  
Do not buy rubbish chinese knock offs.
If you do not want to wait for us to ship coils,  then you can go to your local junk yard (scrap yard) and find SUZUKI SV650 1999  (1999 only!) good condition working coils and try them.
They are BIG, so they may cause issues fitting it!
Hyosung GT650 (2003 iirc) and SV650 use same coils because they are japanese and made by Mitsubishi. These are the “only” korean coils we don’t mind keeping haha.   After  2003-2005 iirc , Hyosung used different coils

Fuel System next,
– check air filter is new and clean ? If i have already send you new air filter, then ignore this
– Carb cleaning by ultrasonic will help.
– Did you replace manifold ORINGS rubbers ?  (intake pipe o-rings) ? Maybe i have already send you new ones ?

[Max]

Hi Marcel,

I have already done valve clearance —> everything in tolerance

Clutch —> Already replaced 🤙

—> air filter new

—> manifold orings new

Regarding the cap, just any cap from a mechanic near by, not even new I think. There were cracks in the previous cap.

How long is the shipping of the coils from the store? Caps would be good too in that case..

What do you think about the CDI?? Not possible that it causes the problem?

[♠️ M77]

Max wrote:

Hi Marcel, I have already done valve clearance —> everything in tolerance Clutch —> Already replaced —> air filter new —> manifold orings new Regarding the cap, just any cap from a mechanic near by, not even new I think. There were cracks in the previous cap. How long is the shipping of the coils from the store? Caps would be good too in that case.. What do you think about the CDI?? Not possible that it causes the problem?

Quote

An NGK cap would be better, some caps have too much resistance. (20 ooo ohms etc, not good for carby hyosung) , Hyosung oem caps are under 10K usually, NGKS would be less, like the ones i keep on the store.

Speaking of store, you will need to send me an email with your address so i can see how long it takes to arrive for the coils.

CDI can be faulty yes but usually when it is dead, it stops sparking.   You may download the GV125 service manual and check resistance of the cdi terminals with a pocket meter.

[Max]

Hello Marcel,
since yesterday the speedo does not work anymore.
which part of the motorcycle is responsible for the speedo?

[♠️ M77]

Max wrote:

Hello Marcel, since yesterday the speedo does not work anymore. which part of the motorcycle is responsible for the speedo?

Quote

Do you mean MPH reading  or revs  (rpm ?)  or fuel gauge reading ?

[Max]

Hi Marcel,

the revs rpm reading, I heard it could be an empty battery.

[♠️ M77]

Max wrote:

Hi Marcel, the revs rpm reading, I heard it could be an empty battery.

Quote

RPM Revs reading comes from dashboard wire that is colour  “Yellow/Black”  (usually)  and it works by signal from these devices  below (so check them)
– Stator
– CDI
– Harness (Mystery sensors inside hardness/ aka. Mystery diodes)
– Ignition Coils

Have a look at this topic below for some ideas on electrical troubleshooting and how to test parts with a meter

It is a GT250 yes but still carby, and they sometimes use same coils , caps,  & regulator as  GV125

No spark – GT250 Carby

Only stator / harness / switches and some other electrical parts are only for GV125 but either way it should give you some idea.

[Max]

Hi Marcel,

Thanks for the info!

I am going to test the mention parts with a meter as discribed in the manuel.

Thanks again for the parts, maybe I get it this time to an end😁

[Max]

Hi Guys,

I have tested the stator and it works well. Also ignition coils and sparkplugcaps are ok, as tested with a multimeter.

The Regulator and the CDI seem to be faulty. The reg is already on shipping, thanks again Marcel.

Can I replace my CDI with any DC CDI from Amazon?

Or can/would anyone recommend an explicit one for replacement??

[♠️ M77]

Max wrote:

Hi Guys, I have tested the stator and it works well. Also ignition coils and sparkplugcaps are ok, as tested with a multimeter. The Regulator and the CDI seem to be faulty. The reg is already on shipping, thanks again Marcel. Can I replace my CDI with any DC CDI from Amazon? Or can/would anyone recommend an explicit one for replacement??

Quote

Sorry for delay.
It should be only a “GV125” cdi specifically for yours.  Because some Hyosung GV CDI’s have 3 plugs and some have 2 plugs.

So i will assume your GV has 2 plugs under it. Replace CDI with the same one with 2 plugs for HYOSUNG GV125 only.

Other cdis from any bike or random ones may not work or will damage parts sometimes.

However, do test your CDI with ohms meter if you can ,  if you can try manualslib website for GV125 Service Manual page for your bike, it will show you how t test cdi.

(((I will upload more manuals on this hyoriders site when i get more time)))

[Max]

Hi Marcel,

I have checked stator (should be ok) as in manuel and mistery diodes (varistors) (should also be ok).

CDI testing was not clear, But it is the last thing which is not replaced or tested in function.

Please help me, which CDI’s can I buy as replacement??

Is one of a GT 125 also possible??

Mine is “CDI Unit Gv 125 32900H G515.

Can you recommend me an link or somethinng to get a new one??

Thanks and regards

Max

[♠️ M77]

Can you attach a picture of your current cdi so we see the plugs , some CDI have 3 plugs and some have 2 and some have 1 (too rare as usually thats for a GA cruise but korea can surprise us with their cruiser variants of bikes)

GT125/GT250 carby bikes are always 3 plugs.

[Author]

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