♠️ M77
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Yes you can but caution the mudguard doesn’t rub. Hyosung GT bikes (all of them) share the same rim. So smaller capacity bikes use 110/70 and the 650 uses 120/60 the mudguard of Hyosung GT bikes accomodate this nicely.
The cams on the rear face up but torwards each other.
But look at the edge of the cam shaft bars and make sure the dark black _________ line is on the same level as the surface of the cylinder head (where rubber gaskets sit)
Both cams must be equal ________ marked to match the surface of the engine gasket area.
Also if i remember correctly (it’s 10pm, so my brain is a little funny!) , the #2 on the sprocket is 100% facing straight up | ^ to match the cam cover holder bolt thread.
#3 on the sprocket for the intake is facing UP but it will be like this / than | straight up
Spin the crank 10x to be accurate and recheck feeler gauge for clearances.
Have you tried everything below ?
Use E5 only
Go to the battery and test these;- What volts is the battery at idle (DC)
- What volts is the battery at 5k revs (DC)
Switch the multi meter to 200 to 500v AC next, while the bike is still running, go and find the location of the stator on left side of the engine.
Follow its wire. Disconnect the yellow plug (3 pin yellow plug), now do the following and report back
- Probe the meter and put both “red” and ” black” probes of the meter inside the 3 pin plug in this sequence.
- Pin 1 & Pin 2 = Volts at 5k revs?
- Pin 1 & Pin 3 = Volts at 5K revs?
- Pin3 and Pin 1 = Volts at 5K revs?
It is a three phase stator, so we check all three lines.There is no need to ground the frame or anything like that, we’re just seeing how much volt the stator gives in AC when disconnected (just the yellow plug!)
GV650, GT650, ST7 = Main major electric faults is usually the bad regulators korea ships with the bikes because Hyosung doesn’t make them, but asks another company in Korea to make stators and regulators.
Stators usually survive okay, but please check the wires are not burning hot or cooking up either, usually happens towards the regulator.
I do not mean to scare you off or anything as i’d want you to just go ride the bike but i’ve had instances where i’ve had to send both a new reg and new stator to folks in Scotland (it’s colder up there though???, i digress!)
Also check service history to see if anything about the injectors have been cleaned etc OR go to Halfords or EuroCarParts and only get this item below:
https://www.halfords.com/motoring/engine-oils-and-fluids/fuel-and-oil-additives/wynns-formula-gold-petrol-treatment-500ml-166754.htmlI do not recommend Redex, it isn’t great, despite its raves about it. Its effective on cars mainly.
If you have time and patience, you may strip the tank and (gently!) , remove the fuel pump and make sure its mesh filter isn’t overly clogged from years of debris or past keepers using junk supermarket fuel. We do not need to replace the pump if it is still working but less clogged mesh is good to improve its fuel flow.
A new pump is quite costly , we have to avoid replacing it. It will last as long as its taken care of
I hope i have made sense in this reply
I would 1000% avoid having pods on a hyosung. You will be in a long abyss trying to make it happy afterwards.
Sorry for the sour news , but really i have tried many setups , the carby motors run best with their airboxes on.
Why not just fit K&N 6507 Air Filter. Mind you, the Stock GT250 air filter is the same as the 650, and the carby 250 airbox has more than enough air capacity to run a 650 too.
What’s the restriction in air ? – The silencing cones that’s inside the air filter, that’s why K&N air filter is just an open hole without the noise suppressing one inside.
I don’t know about USA but here in UK, we don’t really like the sigma kits (wishy washy, and sometimes they make you make modifications to carbs we don’t like, like drilling things etc, it’s very silly).
Is there a local Mikuni dealer around you or any bike shop that deals with Mikuni carbs ? – Get 95 Main Jet Front and 97.5 rear = This is the most max setup. Going beyond 97.5 is wasted fuel really, the bike won’t see much dyno gains after that.
Take a look at these carb links for best set up for your bike
[Tutorial] How to adjust Carb Slide Needle (Tuning) – Hyosung GV & GT 125/250
and this one
[Tutorial] How to swap Carb Main Jets – Hyosung GV & GT 125/250
Also, this is hard to ignore ,but “you will notice this” – Get a FULL Size exhaust can (muffler) and make sure it has baffle.
Zero Baffle = Higher top speed (maybe 2-3mph extra) , same with the 125cc here in UK
Baffle included = More low end torqueModify baffle (make the baffle have smaller hole about the dimensions of a 10 Pence british coin) , bike has better acceleration overal.
Baffle = aka. DB Killer.
Why I said to use “Full Size” cans/mufflers, it is because “tiny” ones or “shorty” ones are pointless and extra loud with no real gains. (no backpressure for a heavy twin that needs a little thrust to set off from 0mph)
Full Size Muffler is similar to size of the stock Hyosung GT250 muffler
Hope this info helps, just my 2 cents 😀
Todays conspiracy: How-come even japanese-made feeler-gauges are made of recirculated British steel from early 70’s?
The Japs & the brits got a little cosy during war days and they both fought wars (to each other and to their enemies) expect them to know how to both work the steel/metals for whatever instruments they made. But ofcouse im going off-track on a bike forum , history is wishy washy so i dare not digress haha
Maybe a little quicker warm up and low speed torque. Nothing more.
Who doesn’t want that, every little helps!
Though back then i had a little fiddle with MS ECUs on other little bikes. But never dared to use a MegaSquirt ECU on an EFi 250 Hyosung (650 yes because very very few have gone turbo on their 650s so they do all sorts to the electrics!) But on a 250 factory bike, hmmm i would imagine i’d only use the MS ECU to custom tune the fuel setup if i used bigger injectors and modified the hell out of the intake (air filter) and exhaust pipes
Send me an email via the site contact form if you require me to try source the parts for you and thank you for the pictures.
You have the Sentec ECU (2008 only era ECU) , very impossible to replace, so please i’d advise making sure no electrics cook it!
I see Simon has got this 😉 , so i won’t disturb you two, he is on a roll here 👍. I assume he will be back shortly after his sunday dinner haha.
Compression-test: 12,5 Bar (F & R) = 175 psi
That’s very very good!
Is this when engine was hot? and both spark plugs were out?Can you wait overnight, wake up in the morning and get service manual, open top valve covers.
Get feeler gauge that is in “.mm” (0.05mm to 0.40mm)And let us know clearances for each valve? Dont do this when engine is warm, it must be overnight cold.
Stator has burnt itself, it does happen.
Can you do the following please?
– Show us the flywheel (for any damage) ? and even the numbers printed on the side of the flywheel.
– DO NOT buy chinese stators on ebay they will NOT work (most of them are hit and miss!) trust me. I own multiple hyosungs & fix customer ones here in north england.
– Can you show us the sensor of stator so i can understand what type it is.
– Can you show us the ECU = Believe me, different ECU’s (There is 4 for GV250 EFi & even the GT has 4 too) require different stators , sometimes “by force” a flywheel that matches is included (Standard KR Motors fashion) , but can still get away using old flyhweel if it matches and keep the new one as back up.Once i have this information , i will read your replies and will also advise you. I made custom orders for EFi including upgrade regulators because i am now officially going to do stator kits for EFi bikes with some custom parts included as one (can’t be split) as a Limited Run basis, that should keep a few more GV250 EFi’s on the road as they are nice bikes to be fair , I like them.
I know you have a GT250cc but remember most of its EFi electronics are robbed from GV250 EFi too.
Perharps its also a good idea to do a thorough look at the bike’s electronics with a meter and service manual, tedious task i know believe me, but least a multimeter can help you check other parts are in spec and not slowly being cooked off (ie ignition coils, ht caps, ET sensor on the engine head, etc)
Keep us posted!
Answered by email , since you sent me an email about it, so will close this topic. But please feel free to make a new topic again if having any other issues with the bike but should be a okay! 🙂
Ride easy now.
What would be the benefit of a booster plug for your GT250 EFi ?
Nice input, i also have a carby GV bike and its harness does not check for clutch switch (incase someone tries to start bike in gear) and no side stand switch connector , this is factory , nothing was cut. It seems later models of GV Korea did not bother adding extra checks thats why the later model of GV carby have 2 plugs for CDI
GT has 3 plugs. I won’t like i did make a mistake many years ago setting off the bike with the stand down lol, i made sure this time i will never forget to check side stand is up before going away.
Good diagram, next time someone has issue with CDI i will also show this topic reply you made showing what each wire does. I knew this already just never found time to make a diagram like you did. Nice job
Yup, China market, would not be surprised if china took some parts from Hyosung and also added inferior copy cat carbs (China will not spend £600 on each bike for Mikuni Japan Carbs) , mind you in china anything can be copied. I just wished they copied the intake pipes as we UK need supplies of them haha.
The green wire from the 250 CDI only works if the 250cc (not 125cc) has 2-wire neutral sensor.
All 125cc have a single wire neutral sensor. So their mod was just wasted cut wire and a placebo effect. Better coils and ignition system like caps / plugs will do a far better job than a CDI cheat (which is really not worth the trouble)
The green wire on the CDI goes straight to the Neutral Sensor Plug
That’s why your 125cc has 2 wires on the neutral sensor plug from the harness , but the ENGINE SENSOR itself has 1 wire coming out of it.
So don’t worry about it.
if the EGR/AIS has been blanked on the engine side, then check under the airbox has been blanked too incase last owner forgot.
Hyosung did away with the ON/OFF Taps on the Comet 125 because owners always left the taps on , and their engines eventually seized to constantly having flooded engines or their carb floats eventually got jammed open as the big tank of fuel is awalys trying to rush through it (incase the pump failed too).
Later Naked 125GT had vacuum taps , and GTR Carby always had it its too awkward to turn the tap off under the fairings , so vacuum tap was installed from the get go. Honestly, the Korea taps work as they should but commonly fail a lot, that’s why i never stock them on the shop.
YZF vs GT = Light frame, it is able to run away quick. A tuned hyo will race past it beyond 88mph indicated (which is the true old gen grey engines did factory) this assumes bike is factory mint and under 1000 miles run in. Old age, neglect of previous owners, bad fuel (eg. E10) , etc will make it run poor. But discussion for another day haha. For now let’s revamp your entire bike to is last nook and cranny down to the engine tappets etc (clearances and compression) will be the last major thing to do (can’t be avoided) , 8 valves it has (most 125 only have 2 or 4 and a single piston)
How well can you work on any motorcycle , ie what is your skill level ?
Can you explain more ?
And can you attach picture of the plugs so we see the sides (threads) and the middle (white center cone)Being FI, did you make any mods to the exhaust or injectors or air filter and what are they (either a picture or show us a product link perharps of the mod changes)
Some Fi bikes can be sketchy on modifications if their sensors can detect that air flow has changed (intake or output/exhaust) the ecu as it is has a small margin of compensation before it leans out
or could just mean the Fi system needs cleaning (as all per above comments) ^
Before we get to the parts, it is still under 1000 miles old, so its very much in the “running in” stages
Around 600 miles , it is mandated for dealers to;
– check valve clearances (must be checked otherwise tight valves or loose ones will have a domino effect on peformance to the engine, carbs, etc..)– Compression Test (very easy) – must be sure the pistons are putting out correct PSI after it has warmed up,
— Warm up engine -> then remove plugs (both of them) –> crank bike for 5 seconds max –> read compression.
Repeat again for rear cylinder tooLet us know the PSi it is doing
Myself and partners here in Yorkshire make CNC pistons which are better quality than ebay ones as true stainless hence warranty on them is lifetime, otherwise we lied. Just refresh your seals or fluid every 2-4yrs (liquids and rubber) – pistons themselves you fit and forget 😉
it could work out cheaper in long as OEM pistons eventually rot, so i make sure my donor bikes don’t have such pistons, i tend to discard them asap unless you only ride in dry days then you will be fine!
