LaserBeam
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I noticed that too, but it happens in UK too. Owners mix cylinders (eg. Front engine use 2016 cylinder with updated tensioner and rear cylinder use 2003 cylinder that uses Generation 1 tensioner)
Oh i see. So your Front Cylinder is from an EFI (Electronic Fuel Injection) bike. Which means theres a HOLE in the FRONT CYLINDER that runs down from the HEAD & out the lower/rear of the Cylinder. It is for measuring GASSES but your carby bike won’t measure them. Have you plugged this hole? It will leak exhaust gasses if you don’t & you will lose some power – reduces the backpressure i think. I’ve been told i can plug that hole on the outside of cylinder, next to the tensioner. There’s 3 holes, the 2 on the outside are for screws, the inside hole is exhaust gas. Luckily i found an old cylinder for my carby bike so i didn’t need to buy an EFI cylinder & different cam chain tensioner & different tensioner gasket.
If your bike was running better before the valve clearance and NEW shims were put in, i’d put the old shims back in.
I’d also check the manual for the TORQUE of the camshaft retainers, just to see if that helps reduce chain noise. Apparently most of the noise comes from the chain hitting the GREY metal piece, i think it’s called a cam chain GUIDE. Check that that baby is not too tight or too loose also. I get ticking noise a bit, mostly when the bike is cold. Usually the front cylinder. I don’t like the noise but mines not that bad.
If your SHIMS were TOO BIG, the cams could be pushing the valves onto the pistons. That will make some noise. Bad noise. Could be terminal if left unattended. Won’t do much for the compression either. I’d check the shims again before doing the cam chain, unless you are sure the chain is buggered as i don’t have a puller to remove that flywheel & i kind of like it where it is. 🙂
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syazel, i tried to send you a personal message, not sure if this site allows it. I’m not going to put the link to the carb parts here, i don’t think Marcel will like it. What i am going to do is post pictures of 2x carb kits available now. I think you will need DIAPHRAMS & possibly the FLOATS, although it’s best to keep the ORIGINAL FLOATS if they haven’t been messed with as they will be set at the right height. Sugest you buy the flaots anyway just in case. Some kits come with needles but you should be able to clean up your old needles. Try to get a Carb Kit that looks like these:
You can easily put all these new parts into your carbies, except the long, thin, pointed part with the fat screw thread on the top of it. This is the mixture screw but it is SET BY FACTORY and you shouldn’t need to touch it. To get to it, you have to DRILL it out. I never needed to touch it. All my satisfaction came from the other parts. I especially like the big golden cylinder. It has a ACORN HEADED SCREW on top and it just slides out. Your needle slides in and out of this and it’s a good idea to swap it for new one. The FLOAT SEAT has an O-ring around it and a filter screen. I am sure you need a new one of those on each carb. The FLOAT NEEDLE drops into it. This little needle has a button on top of it with a spring inside. I am pretty sure your springs will not be springey anymore. The first kit is the one i suggest you buy. I have a link to a picture tutorial on how to service these Hyosung Dual Carbs & will post it here when i find it. There are MANY carb kits where you shop but make sure you get one that looks like my photos – they are a bit more complete than most kits. You can do this job if you can undo screws & you are not heavy handed. Be carefiul undoing the ACRON SREW it likes to break – it’s thread is small & it’s BRASS so it’s brittle. HEAT the CARBYS really well before you start the job. Heat the silver meatal around the screws & heat the screws too. Mostly make the carby HOSUING hot so the heat expands the casing and allows the screws to undo easily without breakage. Marcel has some good guides here & i will upload a full photo walkthrough for you. If you can’t fix the carby with this kit you WON’T have lost much cash. If you ultrasound the carbs you will lose cash as you’ll still need to replace all those bits. They have to take carb apart to clean it & they may wreck it in the process. What do they care? I’d also look for a used Carby from a wrecked Hyosung too, if i couldn’t repair mine. Once you’ve done the job, you’ll realise it’s easy & is better done by somone who gives a sht about the carby. You got this, mate.
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I will send you a link to a carb kit & guide on how to install the bits. It can be easy but apply heat to the brass parts before your undo them .. heat the carbs all over thats what i do. Very hot. A bit too hot to touch, not too hot you cook the orings inside. Ultrasonic clean will cost too much but is a good alternative IF they look after you carbs. Can of Carb Cleaner, some tools, a table, a chair, some parts & you can make them better.
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Hi Maciek. Your REAR CamChain TENSIONER is not the right part. Your Front tensioner is the correct part. It’s 27.1 mm in diameter, from memory. Try a wrecker or new aftermarket part to see if that eases the noise.
The manual says to TURN THE MOTOR 10 times, at least, before measuring VALVE CLEARANCES. Pop the right shims in both cylinders and it will sound & run better. I didn’t read all your post – is your rear cam chain ruined for sure? It may not be idk.
When you lay your cams on the head, place the cam that’s furthest away from the tensioner, on first. After i lay the 2nd cam down, under the chain, i press my finder in the TENSIONER HOLE to apply the pressure to the cam chain, so i can see how it will look when the tensioner is installed). Then i release the pressure & rotate this cam until its in the right spot. Bike will run with the cams out a bit but it sounds bad & the bike doesn’t like it. I use NGK CR8E spark plugs & testing CR7E from memory.
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PS. Marcel may know where you can access a Carby Service kit & a way to get it to Poland. Good luck.
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d entire fuel tank into the engine
I serviced my carbs and replaced most of the jets & gaskets. Spray it all clean with Carby Cleaner & replace as many of the parts as possible. A carby repair kit won’t cost much. HEAT the Screws abd JETS before removing them so the brass doesn’t break. It’s fairly easy job & should improve your carbs. If not you should try to find WRECKED Hyosung with the same carbys. I’ve got 2x carbs & serviced both. You can get a new dual carb from Hyosung but costs almost as much as the bike. I alos found a similar dual carby that is the same size but has it’s throttle on the other side. I intend to see if i can move the throttle cable across to make this carby work, but it may not be that safe. It is for the Honda Rebel 250. The dimensions are the same so it will fit but i’ve not tested it yet. It is a very cheap priced aftermarket carburettor but it looks ok in quality. Cost me only $35 quid. But your best bet is to find a used Hyosung Mikuni carb & service it, if your own carby does not come good after a clean. They are MECAHNICAL so parts can be replaced to make them work again. My guess is your FLOAT NEEDLE is not sealing off the fuel correctly. Perhaps it’s O-Ring has failed. It is a cheap and easy part to replace. You don’t have to get the Mikuni parts to test if you can save your carby. replace the bits you can & spray the hell out of eeryhting in there. You can also get CARB JET FILES which are just peices of wire you poke in the holes of the jets to clean them. A strong Carby Cleaner spray can should do most of the cleaning for you. Marcel has some guides on removing the carbs and opeing them up and tricks like adding a bit of vasleine to the gasket and the diaphram to create a good seal, etc. If you have trouble removing a part or finding replacemet parts, you can contact me.
Hyosung BDS26 Dual Carburetor :
Aftermarket PD26JS Dual Carburettor for HONDA Rebel 250:
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You can get valve compression tools that cover all sorts of size valves for only a few quid which will do the job Quote
Thank you Simon. Bought a Valve Spring Compression Tool Kit. Won’t know if it works until i try it, which is not the way i like to start the job. Bought a FULL Cylinder/Piston kit but it never arrived. So i bought the parts individually. Will be the 2nd time i’ve done my clinders & pistons – i honed the old cylinders but they’re not perfect.
Bought a Piston Kit, a rear Cylinder, Head & Cylinder Gaskets, Intake & Exhaust Valves, Valve Oil Seals & Valve Collets. All i need is a Front Cylinder & possibly a new set of Valve Springs.
57mm Piston & Rings Set:
Valves, Oil Seals, Collets:
Valve Spring Compression Tool Kit:
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Marcel the manual is not going to tell me to buy a Hyosung Valve Tensioner is it? I gave up looking for one.
I thought the shop sold the valve oil seals & hoped you’d have one handy. 🙂
How did you guys remove & replace your valves. A link to a valve tensioner that worked on a hyosung would help a lot.
Removal can be done with sockets i think but if anyone knows the best tool for the job, i’d like to know it please.
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Electrolysis works really well for rust removal. For sure check out some videos of the process on YouTube, it will make it easier to understand. Once finished, tip out the solution & rinse the tank out with a bit of unleaded or diesel. Slosh that around so it COATS the ENTIRE INSIDE with fuel & tip it upside down and slosh it around as you pour it out again. This will coat the walls & prevent it from insta-rusting … think they call it flash rust, where the newly cleaned metal starts to oxidise instantly. The oil in the diesel or unleaded will coat the metal and protect it a bit. Can rinse tank with distilled water then rinse with fuel. Should be ok to just rinse it with fuel a couple of times.
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-Remove LEFT PASSENGER FOOTPEG (not the right).
This allows the plastic mudguard to more easily slide out & be returned into place.
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Sweet, thank you. Yeah i went to a wrecker to have a look at the EFI Cylinders. The 3 x holes i don’t have on my Cylinders are for exhaust gasses (sensor). Apparaently i can just plug those holes up & use the EFI cylinders on a carby model bike. I need to buy 2x newer Cam Chain Tensioners & Gaskets to make it work.
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How easy is the rear shock to adjust and is the rear shock easy accessable do I need to remove fairings or mounts?
If your rear shock is SOFT & boucnces up & down easily, it’s toast.It is very easy to swap that old shock for a new one.Here is how to do it:PS. If you need more specific info about Socket or Spanner sizes for this job, let me know.-----LaserBeam---->
The secret to replacing the REAR SHOCK GT250R:
-Remove seats
-Remove 2x REAR fairings
-Unscrew CDI box but leave it connected
-Remove Battery
-Undo 2x Bolts inside the pillion seat box
-Undo 2x Bolts & remove Metal Bar from under rear mudguard (located under battery)
-Undo REAR Footpeg (Right Rear Footpeg from memory)
-Undo 4x Bolts of Rear Brake Light Housing (hang it from bike with cable-ties, etc)
-Remove Bolts holding the Rear Mudguard
-Slide MUDGUARD backwards & pull it towards the side of bike where you removed rear footpeg
-Leave Mudguard, Brake Light Housing & Indicators on bike but secured & out of the way
-Now you can easily SEE & ACCESS your REAR SHOCK
-Place a JACK under REAR of bike to take WEIGHT OFF the SWINGARM (Jack to FRAME just infront of SWINGARM & not on exhaust)
(find HEIGHT SWEET-SPOT where SHOCK BOLTS are easy to remove & replace as they have no load on them)
-Apply HEAT to the Linkages & Shock Bolts
-Undo Nut from Both Linkages but LEAVE THE BOLTS IN & let Linkages hang
-Can use RING SPANNERS to LOOSEN Rear Shocks Upper & Lower Nuts (i hit spanners with hammer but can use Breaker-Bar)
-Remove Lower Shock Bolt
-Hold Shock & Remove Upper Shock Bolt
-Lift Rear Shock up & it’s out of there
-Lower NEW Rear Shock into place, Insert Upper Bolt & Lightly tighten Nut (i add Lithium Grease to bolts & nuts of shock & linkages)
-Insert Lower Bolt & Lightly Tighten Nut
-Check HEIGHT of your JACK (May need to LIFT or LOWER the bike to get Bolts in nicley)
-Tighten Upper & Lower Shock Bolts
-Replace the Shock Linkages on the Left & Right & Tighten
-Lower the bike off the Jack & push the rear of bike down to test
-If nothing is BINDING, slide mudguard back into place & replace bolts & fairings (Don’t forget the BAR – it supports the weight of your battery)
PS. If you fully remove the Mudguard, you’ll have to undo your indicators & it will be a bit harder to replace it – don’t bother, just pull it back & to one side
PPS. Fast & very easy job – i was suprised. Hardest bit is undoing the Shock Bolts with the little ring spanners i used. 😀
Original Hyosung GT250 Shock Absorber with Bolts & Linkages Connected
Newer version of the Hyosung GT250 Rear Shcok Absorber
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Just picked up a 2017 GV650 that has an odd issue, after being left unused for a few months, the odometer has reset itself to zero ( Anyone faced this issue before? Quote
My 2008 GT250R had only 2700km on the clock in 2024. Some reset themselves at 40,000 or so. How annoying is that? And what a pain for the buyers. But i’m not putting miles on the clock to lower – that just lowers the value of your bike. The law is different in places so it’s hard to say what you should do. The cops here know my bike odometer is lying but they also know the bike was registered and sold like that, so it’s not me they want. Although they could take my bike off me. But they’d have to catch me first.
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Is there any olace where i can get new/used carburetor for gt 125 at reasonable price? Or maybe some substitute made of chinesium exists that will fit in this model? Im getting preety depressed cause i cant find any in normal price range.
Hi Safaratrew, i bought a Chinese Dual Carburettor for my GT250R. It’s called a PD26J. It’s a replacement Carb for Honda Rebel CA250Â CMX250.
It is almost the same as the Hyosung dual-carb but the throttle rotates the other way. So to fit it to our bikes we need to re-route the turn the bracket, for the throttle, around. I am hoping this will be easy to do but have not tried yet. The carb looks very similar. It is so cheap that there was no excuse not to try it. It cost me AU$65 (like 25quid). I may have to take the throttle bracket off the Mikuni Carb and swap it over, im not sure yet. Worth trying the PD26J i think.
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Jake C i adjusted mny idle speed to between 1100 to 1200 RPM at idlle when the engine is WARM. Closer to 1200RPM will probably suit most. If i put the idle to 1500 RPM it makes it hard to shift the gears into NEUTRAL. Lower revs at idle fixed that and it uses less fuel sitting at the traffic lights.
Your bike may just need more air into the carbs but i would replace the 2x FLOAT- VALVES and give the carbies a good spray with CARB-R-CLEAN by CRC or similar product.
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I installed the rear shock absorber 4 hours ago. Anyone wants to know how to do it please let me know. The 2x videos i found on the subject were wrong and make it difficult. I had another idea and it worked beautifully. Hyosung sold me the shock but the spring looks the wrong way round. I left it like that to test it. Seems firm but its ok. It’s much better than the pounding my old shock was giving my backside. Thing must’ve been half siezed. Rock soild impacts to the backside aren’t much joy. Feels like a motorbike is meant to feel. Stoked.
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I have a 2005 GV250 that seems to be running way too rich. The CR8 plugs in it are consistently wet . Carbs were cleaned last year, fresh gas, decent spark. At idle when cold I have visible fuel vapor from the exhaust. It clears up when warmed up, but you can still smell the fuel.Quote
My 2008 Gt250R also ran rich, even before i put 90 & 92.5 JETS in the carbs. Jets are super easy to swap over, just unscrew them & screw a replacement in.
1. Did you put new FLOAT-VALVES in the carbs? Very easy to do. Keep your original FLOATS as their height should be good, but change the float-valves if they not new.
2. I removed the AIRBOX completely from my bike. I put 2x AIR-FILTER PODS on the top of the carbs. Fixed the rich running bike, sounds freaking aweome & i have all this room under the tank for more air-cooling & i intend to put some HEAT-INSULATIUON under the tank to keep my fuel cooler.
3. I had great success smoothing out the fueling by TURNING the IDLE SPEED DOWN to about 1100RPM’s. The manual says to set them to 1400-1500 RPM. But i found if you lower the idle speed the bike is much smoother acceleratiing throughout the entire rev range. The only problem is it makes the bike a bit harder to start. But only because i don’t use CHOKE to start the bike – the choke floods the carbs at the slightest touch. My carbs were toast & i haven’t fixed the choke but the bike runs well.
My carbs are not great but they were really bad and caused big FUEL Leaks into the carbs & into the airbox. I never fully fixed the carb issues – they still leak a little fuel into the air-filter but i can redline my 250 now and get about 150+km/h so it’s not bad.
I bought a Chinese dual-carby to try out, but the throttle is not in the same position so it may not be able to use it.
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