GT125R wont start
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Hi all. Bought a none runner GT125R as a project. Long story short wouldn’t start. Turns out engine was shot. Sourced and fitted a used engine. Whilst doing that i fitted upgraded fuel lines, bigger fuel filter, upgraded vacuum pipes and the EGR blank. Also fitted a new Yuasa battery. Bike came with a few spares inc a new Starter relay as the old owner knackered it from trying to start the Bike. I fitted this to. It wouldn’t start unless i bridged the starter relay. Nothing at all when pressing the start button. So i ordered a relay and fitted it. Still the same issue it wont start off the switch. Any ideas on what to check?? Price of the bike plus other bits currently stands me at around £1000 and it wont start 🤬😭
Also smells like its running rich 🤔
Any help is greatly appreciated.
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Hi Cpt
You are having a struggle, I am sorry for that. But you are so near to it all working, do not give up yet.
The starter circuit is very straight forward.
By shorting out at the starter relay you show most of it works, the engine is good to go etc. Easy to short rich or lean mix when you have her started. Much on here about mixture. My GV was messed with by over jetted and over rich both on mix screw and needle height by previous owner. You willl find that out when you start running it enough to colour the plugs.
The starter circuit has to have three things all work to fire the starter relay.
– First the starter fuse needs to be good.
– Second the ignition switch needs to be correctly passing power through it.
– Finally the handlebar starter switch needs to connecting when pressed.
The series of three can be checked easily with a multimeter.
Bet it is the fuse or starter switch.
Fuse easy replace – do not short out fuse replace it. Fuses blow as a protection so probably blown by old relay failure.
Starter switch issue, my old Yamaski had this issue and electrical contact cleaner spray sorted it. Just spray in switch on contacts and operate switch multiple times to clear carbon scoring/dirt off swith contacts (unscrew from handlebars and spray onto internal contacts).
Good luck.
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If it turns out to be a wiring harness connector in the starter circuit then it can also be cleaned with contact cleaner by unplugging conn, spray in conn and push fit and disconnect connector multiple times to clear dirt etc.
Just trace it all through with a multimeter and she will start on the button.
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Had a thought whilst out mowing lawn. If you find a burned harness conn or the new starter relay is no good message me. I will send FOC as have spare knocking around.
Also do not be tempted to scrape/sand any connectors/contacts. They will work first off but will corrode very fast to soon become unuseable. Isopropyl alcohol can be used instead of contact cleaner to clean contacts etc.
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Thanks for commenting Tom. Just frustrating i’ve come this far and now it wont start 😖 I’m Pretty sure its a wiring issue. Indicators and pass light wouldn’t work but when i jiggled the wires they worked. Looks like it’s time to check all plugs and wiring again. Both fuses on the bike are ok to. So i’m guessing it’s from the switch to the starter relay that theres a problem. Getting a multimeter tomorrow to start checking continuity between wires. Luckily i’m off work monday so can have a look without the kids being around.
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cptpickle I am sorry to hear that, electrics are a daunting subject that is actually very straight foward. You can do it and I can show you how, I am a qualified electrical engineer. The wiring loom and connectors can look like a big nasty birds nest wrapped in tape, you do not have to unravel the birds nest just test accessible bits of it.
You just need a simple multimeter for a £5 and some contact cleaning spray again about a £5. It should cost you nothing more to get starting circuit working and the spray will most likely cure the indicator gremlin. As you have said already the bike’s bolts were decayed badly, that means she has stood outside alot so some of the exposed wiring connectors and switches will be dirty and perhaps have some corrosion – easily fixed with the spray.
You will measure resistance if you have to test if wires and see if the connections are good (resistance shown by an solid triangle pointing to a vertical line or the ohms setting shown by an Omega symbol on the multimeter). For voltage being present you want use D/C current (a straight line with a dotted line below – A/C is a wavey line). You would use A/C settings to test output from some stators before the rectifier – your stator works fine.
You have an earthed negative frame that is always the negative connected straight to the negative on the battery via a fat copper wire. This makes it easy using a multimeter as any exposed metal (engine case / frame bolts etc) is an earthing point(negative) for the multimeter. To track electrical faults is a methodical task but not difficult one.
I have a GV with all the same wiring, wire colours etc and can post pics on where and what to check. Also Marcel has seen almost every issue with Hyosung, he always helps.
I will see if I can track down a wiring diagram for the GT/GTR, this will give us an easy guide to follow with wire colours and routes etc.
You have already overcome the largest problem and the starting circuit is just a minor wrinkle in the whole show. Most people would run away at the thought of an engine change – hellfire, you did it first time and it runs!
If you sell on now you will give somebody a bike that you fixed all but one or two very minor issues. They will quickly clean the connections and be quids in
You can do this – easily!
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I did reply but it disappeared when I edited a spelling mistake.
So sorry if this duplicates it if it appears.
cptpickle I am sorry to hear that, electrics are a daunting subject that is actually very straight foward. You can do it and I can show you how, I am a qualified electrical engineer. The wiring loom and connectors can look like a big nasty birds nest wrapped in tape, you do not have to unravel the birds nest just test accessible bits of it.
You just need a simple multimeter for a £5 and some contact cleaning spray again about a £5. It should cost you nothing more to get starting circuit working and the spray will most likely cure the indicator gremlin. As you have said already the bike’s bolts were decayed badly, that means she has stood outside alot so some of the exposed wiring connectors and switches will be dirty and perhaps have some corrosion – easily fixed with the spray.
You will measure resistance if you have to test if wires and see if the connections are good (resistance shown by an solid triangle pointing to a vertical line or the ohms setting shown by an Omega symbol on the multimeter). For voltage being present you want use D/C current (a straight line with a dotted line below – A/C is a wavey line). You would use A/C settings to test output from some stators before the rectifier – your stator works fine.
You have an earthed negative frame that is always the negative connected straight to the negative on the battery via a fat copper wire. This makes it easy using a multimeter as any exposed metal (engine case / frame bolts etc) is an earthing point(negative) for the multimeter. To track electrical faults is a methodical task but not difficult one.
I have a GV with all the same wiring, wire colours etc and can post pics on where and what to check. Also Marcel has seen almost every issue with Hyosung, he will help.
I will see if I can track down a wiring diagram for the GT/GTR, this will give us an easy guide to follow with wire colours and routes etc.
You have already overcome the largest problem and the starting circuit is just a minor wrinkle in the whole show. Most people would run away at the thought of an engine change – hellfire, you did it first time and it runs!
If you sell on now you will give somebody a bike that you fixed all but one or two very minor issues. They will quickly clean the connections and be quids in
You can do this – easily!
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Thanks for the reply Tom. Just got so disheartened with it. Sort 1 thing and another fault pops up. I started at the end and worked back. By shorting the starter Relay i know the wire to the starter and the starter it’s self are ok. Bought a multi meter to test wiring. Followed the wiring from the switch into the main loom. Where i found a connector just above the front cylinder. Directly in the area most likely to get wet 😮😟 it wouldn’t budge. Managed to separate it and it’s full of dirt and salt etc and all pins are green and 1 corroded away. So due to the state of the wiring i’m thinking a new loom is the way to go. As i could replace the connectors but could have further issues down the road if the wiring compromised. Plus new loom is less messing about and rules out that side of it aswell as the side stand switch (which has been bypassed) Which narrows it down to either the loom or R/H switch. I do have a spare engine with neutral sensor etc i can swap over to.
I don’t want to get rid as it’s my first road bike. Just so annoying fault after fault after fault. Suppose once i’ve replaced everything i should be trouble free riding for a while 🤣🤣
Thanks Again Tom 👍
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Tom has been helpful in your diagnosis , so go with what he says because i deal with wayyyyyy worse hyosungs and i usually have them running within a week. I am in yorkshire, so you ain’t to far fella. But don’t race to bring the bike to me just yet since i have faith you will be able to work on it and your hands are free labour.
Hey, if you crack this thing, you will be half-way being your own self-hyosung wizard!
I wont lie I wish korea spent more time in the electronics sector , but i can’t entirely blame them as my own inlaw has a new 2021 Jap bike thats flashing EML light and has been happening since the rains of 2021. The weather’s elements can be unforgiving, thus any bike i own personally i am usually ocd by;
– re-wrapping the harness all over tight , tight , tight.
– using “Suzuki Harness Boots” to hide any plugs subject to water attacks
– using ACF50, in every terminal, just a tiny bit , even if one bike doesn’t see rain , but least i can aid in preventing some form of oxidization. (Oxygen + Steel is a constant war, in of itself. but don’t panic, we have ways around these things to keep our 2 wheels longer)Remember if the loom is great (fixed or inspected by you) then this is the usual sequence to start the bike;
– Is Neutral ON?
– Is the kickstand switch bypassed (yes , but don’t forget to always PULL in clutch when starting, fake neutral starts are rare but can happen and bike falls to the ground!)
– Is Clutch Switch Sensor ok ? (Multi meter = ohms in zero will mean its dead if you squeeze the clutch handle lever on / off , it will mean the circuit is dead)
– is the CDI ok ?
– is the Stator Pickup coil connected? (critical) = no stator, no sparks.
– is the stator 3 yellow plug connected (not critical to “ignite” the bike)
– bike rolls freely (real neutral) (this is on you to make sure just in general)
– Solenoid OK? (it will make click sounds if its dying or needs replacing)
– Battery is 14BS? (OEM size for GT bikes of any CC)
– Battery is not old ? (Hint = just turning on the bike, the volt meter will quickly drop from 12.8v to 10v in matter of seconds) (Replace it.)Garages have a special yuasa analyzer that can check your battery and their screens will either say “battery good” or “battery needs replacing”. They do this for free anyways.
– Kill Switch Red Button is “pressed down” ? (towards you)
– Start Button isn’t broken?Press start ==> check plugs for sparks ….
very Dull yellow sparks = Replace battery (common, winter is usually the harshest time for them), or check coils (common) or plugs (faulty plugs) or fishy HT caps ? – ensure plugs are CR8E ,dont buy LASER PLUGS until it runs. Its cheaper to run through basic CR8E for now . Don’t bother with Blue Box Iridium IX as the Hyos don’t like them much but yes they will run with them.
Hope i have made sense!
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Thank you Marcel.
Cpt – post a pic of the connector block and I will post you a replacement with instructions of how to replace the original (no special tools required) or just that bad pin incase you need it. Message me an address or I can send via site admin if necessary.
That connector block sounds like the issue, or a least one of the culprits.
This is the how I would check starter circuit if my GV had no solenoid click and no starter turning over but all lights etc work. Sorry for length.
1 give starter soleniod a fair tap with a 22mm spanner sized object and see if it tuned over. No luck then number 2
2 check voltage is reaching solenoid at its connector. Set cut off switch set to run and with starter button pressed. (select on meter DC voltage ’20’ put red probe in brightest coloured wire and black pobe on exposed frame metal/bolt/engine/battery neg post). No luck number 3
At this point you could feed 12v directly from batt down a old bit of wire to the solenoid. Because you have two wires connecting to solenoid the second will go need to go to ground (somewhere on frame/ batt neg). Just a quick touch of 12v will tell you if it is all good with solenoid and starter turns. The black wire is usually the negative/ground, I say ‘usually’ as I have seen all black wires with no labels before.
3 Fuse, is there 12v? Does 12v pass through fuse? (same proceedure select DC voltage ’20’ probe connections with red probe and black to neg/ground). You should have power here, if not trace back, if you have 12v do step 4.
4 Starter switch and engine cut out, because I have all lights and neutral I am assuming ignition switch is good. Undo the two screws clamping switch holder to handlebars. The throttle cable will be restricting access to the lower part, the top part will lift up enough to clearly see inside.
I would test the engine cut out first as I have easy access.
In photo below (different bike switches and horn side not starter but they are all pretty much the same inside) you will see red arrows, these point to the contacts inside the switches, they are very exposed. When you operate the switch you will see the switch internals move inside connecting/disconnecting. You also see the wires soldered to each switch, which gives you the colours when you have no wiring diagram – note the wire colours to each switch. With continuity selected (see photo below) hold the multimeter probes on the soldered wire contacts on the switch (if there are three wires to a switch the middle is usually the feed in and the outside two the two switch outputs). Test switch on and off positions with your multimeter. The meter will read ‘1’ or ‘OL’ for open circuit (switch off) and ‘0.0’ for closed circuit (switch on) . If in doubt of what reading is what set multimeter to continuity look at screen and touch probes together, touching probes is a closed circuit (switch on). Some multimeters beep with closed circuit which is great if yours does.
Now turn on ignition and see if 12v is present and passes through the switch. Set multimeter to DC voltage ’20’ and put black probe on frame metal whilst then touching red probe to each soldered wire contact in turn. Check On and Off positions. Screen should read around 12v.
If that cut off switch is fine then the starter button.
Wiggle throttle cable off throttle grip and expose lower switch case. Note wire colours. Again same test proceedure, check continuity with starter button pressed and released. Then check 12v.
5 Diagnosis.
– If I have 12v at fuse, and 0v at the switches but the switches show continuity then the issue is after the fuse and before the handlebar switches (ignition area/ conns/ wires).
– If I have 12v at switches, on and off have continuity and 12v passes through both of them then the issue is after the switches in the loom connectors or wires leading to soleniod.
– If I have 12v at only one switch but both switches show good continuity the issue lies in the connecter or cables of the handlebar switches you are working on. The 12v often passes through the first switch, back to the connector block where a spare pin is used to link two wires feeding the 12v back to the second switch. If there is no pin often it is two wires twisted/crimped together inside the wires sleeve/wrapping.
– If 12v reaches switch but not passing through (no continuity) then spray contacts with cleaner and move switch through On and Off 20 or so times and test again. If necessary repeat a few times, if no joy get new switches.
This photo is of left side pitbike switches but it will show you what to expect inside. I also put a multimeter with meanings to symbols. Red arows show exposed switch contacts.
That is how I would trace it in the loom. To test a wire you select continuity and put a probe on each end looking for the closed circuit. If you cannot get closed circuit wire is bad and replace.
To test conns, stick probe in one side contacting with the chosen connector pin. Do the same with the second probe on the corresponding connector pin on the other side of the connector, again looking for closed circuit. No continuity means bad pins.
Since the wire colours where noted and I know the order of the switches etc so I therefore know the direction the 12v starter signal in travelling in the loom. It is easy to chase that colour wire through the loom and connectors checking continuity as you go. The loom is not big and solenoid and battery placed central to the bike with switches up front, there can only be so many connectors and wires involved. If you get lost halfway through loom test from solenoid back to switch.
When using the meter’s probes often a layer of oxidisation/tarnish/dry flux will stop connection. You may have to scratch and dig a little to get contact. If in doubt select continuity and put both probes on the same contact, only touch the contact with probes not the other probe. Look for open and closed circuit, closed means you are getting a good connection.
Sorry for length, hope this helps and is not complete confusing waffle.
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Another tip. When in pairs of wires, like to the solenoid, you have a positive(input) and a negative (output). Usually, not always, but usually the brighter colour is positive the darker is negative. This will apply to stereos, houses, cars etc. Look at your home 240v power cables. Blue is brighter than brown, blue is positive and brown is negative.
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Eurocarparts have contact cleaner for £4.39 https://www.eurocarparts.com/p/holts-electrical-contact-cleaner-500ml-552996200
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Sorry i made a mistake in my post, wont post late after a beer again.
You can ignore the engine cut off switch as you know it works from when you shorted the solenoid because the bike started and ran rich smelling. So checking that is pointless even if you are in the switch housing. Because she started this also means the clutch switch is probably ok.
Also, it is the start button and lights that often share a common 12v feed. That shared 12v input is split between the lightswitch and the starter button creating 2 different circuits (starter and lights) from one 12v fused input. The engine cut off switch, like the side stand and clutch switches, are part of a spark inhibitor circuit which means the engine will turn over but with no spark.
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