No spark – GT250 Carby

[Hyo71]

Hi,

I’ve got a carb’d ‘parts’ bike that came with a running race bike I bought a year ago. The carb’d bike was a race bike but blew the rear cylinder. It was completely stripped of all parts (except for the loom) and I am now trying to put it back together without knowing how it came apart. Hyos are fairly new to me but I have a manual but I’m not sure exactly what year carb’d bike I have, so I’m not sure if I have the correct manual – it has wiring diagram for efi fuel pump but then has carb info (?).

Anyway, heres the situation:

• I’ve got the engine, carb, fuel and vent hoses all connected.
• I’ve got a good battery hooked up.
• The neutral light on the dash is on, turns off when I put it in gear. The drive sproket spins freely in neutral.
• Side stand switch wires are joined – found them like this
• Clutch switch wires were not joined, but wiring diagram shows them as joined for ‘Run’. I’ve joined them – makes no difference to my spark issue below.
• Spark plugs cleaned up and gaps checked – they were fine
• Main fuse is fine – I only seem to have one that I can see. Are any others needed to run the bike? Its a race bike – no lights, indicators etc.

I’ve turned the key on, dash lights up, switched kill switch to ‘run’, hit the starter, bike cranks over strongly, choke on, but it doesn’t fire. Try a few times, battery and starter are going strong non stop but still not firing. Fuel is definately getting to the carbs as I can smell it in the exhaust and my bottle is draining. Pull front spark plug out and plug it into the spark plug lead, hold against cylinder and try starter again – no spark. Try rear spark plug – no spark. Take spark plug out of plug lead and put small file into spark lead and hold near cylinder – no spark on either front or rear.

I’ve taken the coils off and sanded the earthing points on the frame to bare metal. I did the same for the battery earth. I’ve cleaned out the primary connector wires and scrubbed up the tab that the wires connect to on the coils – still no spark

Testing the coils I get:

Front – Primary: 0.1 ohm

Front – Secondary: 14.7 Kohm

Rear – Primary: 0.1 ohm

Rear – Secondary: 16.48 Kohm

I bought an auto ranging multimeter for this project but I didn’t realise it didn’t read to 2 decimal places. Looking at the manual my range should be 0.19-0.24 ohm and 5.4-6.6 Kohm – if I have the correct manual. Can anyone confirm if my manual is correct?

Testing check:

Front – coil only – 6.13 Kohm, lead only – 0.0 ohm, plug cap – 8.67 Kohm = 14.8

Rear – coil only – 6.19 Kohm, lead ony – 0.0 ohm, plug cap – 10.39 Kohm = 16.58

In my mind, the coils are my issue with resistance that is too high. My only issue is I don’t know if I have the correct ranges from the manual. I’ve pulled the CDI and regulator rectifier out to check with the multimeter but the diagram I have for the CDI has 2x 4 pin connectors. Mine is 2x 4 pin connectors and 1x 2 pin connector (10x pins total). I thought I’d test the coils off my efi bike so I took that apart only to discover they use different coils! I don’t think the RR is my issue as the bike should still idle without it kicking in .

Any ideas??

 

 

[♠️ M77]

I will report back, hold tight for me.

[♠️ M77]

Hey,

Have you had a chance to test the stator ? Since no sparks will happen if this unit is dead.   Check the resistance of the coils (3 yellow plug) and also critically the “pickup sensor”

if possible, also post a picture of the stator and your flywheel and i will confirm if they match each other.

Also while at it, under 1000 ohms or 100 ohms, test each single wire from the CDI plug to the relevant wire colour that corresponds it to rest of harness.

Ie. Blue = stator , green = stator ,  black with yellow line = front ignition coil,  blue with white line, rear ignition coil , that’s just at the top of my head 🙂

[Hyo71]

Evening,

I thought I would bring the problem solving for the spark issue back to the Tech Help section so as to help any others that may have a similar issue in future  (as opposed to the Project thread I have).

I had a chance to check the 3x yellow wire plug (Charge coil). I got 109 ohm. Spec tolerance 90-110 ohm. So ok there.

The Blue + Green wire plug (pick up coil). I got 0.6 ohm. Spec tolerance 0.6-0.9 ohm. So ok here as well.

I hadn’t seen your post Marcel so have’nt taken the stator cover off for a photo. I’ll pop it off next time I’m in the shed. I had already sort of checked the CDI/loom, but I only checked using the continuity function (the buzzer), not the resistance like you mentioned. Is chekcing with resistance better?

Using the buzzer there doesn’t seem to be any breaks in the loom and the wires align with the wiring diagram (mostly). I’m getting continuity from my CDI to all of the key components regarding ignition/spark. Likewise for the regulator rectifier.

I tried my replacement coils but that didn’t solve the issue, so back to the drawing board.

I tested the rear ‘brick’ diodes with the 3 wires (Blue/yel, Blue, Green/red)  and came up with the following readings on the diodes;

• B/y = 0.512v
• B = N/A (signal to CDI)
• Gr/r =0.576v

I opened up the mystery black ball thing which had a yellow sensor (?) thing and 2x diodes. It has 3 wires (Black/brown, Black, Black/white) and testing them I came up with the folling readings on the diodes;

• Blk/brwn = 0.190v
• Blk = 0.185v
• Blk/wh = NA (earth from yellow brick thing, to earth for rear coil)

When I carried out a buzz test on the 2x diode wires, they colour match 2x black rubber covered plugs that pop out the front of the frame and buzz. They almost look like wires for a horn but they don’t align with the colours on my wiring diagram for the horn. Being a race bike all road items (horn, lights, indicators etc) where removed and I can’t find the corresponding plugs – could they be for a 2x wire indicator relay? I’ve had them before but the wiring diagram shows a 3x wire relay at the rear of the bike. These wires are at the front.

I carried out a resistance test on the CDI using the pin table in one of the manuals I found on this forum. I’m not getting a single match. For reference, my multimeter is auto ranging.

My next steps are to borrow a CDI off a known running bike and take the cover off the stator for a photo. Failing those, I’ll try source another loom/harness.

Any ideas people?

All the pen ‘ticks’ are the wires I’ve checked for continuity.

 

Neutral diode circled in red.

 

Mysto yellow sensor with 2x diodes. This was heavily wrapped in a black ball of heatshrink. Red and green lines just to give you an idea of wire runs goining into harness and coming back out to the 2x rubber plugs. Note Blk/wht wire from yellow sensor going to earth at rear coil earth.

 

This is where the 2x mysto wires/plugs come out. I dont have corresponding plugs.

 

[Simon]

That could be the horn

[♠️ M77]

The 2 black spade connectors going towards the oil cooler is for the horn system.

I know even the 650 has a wiring diagram that says “igniter” on it and it is usually a strange mystery object or plainly exposed , however korea makes the harness.

Otherwise if there isn’t some sort of mystery sensor for the coil at the front section only , then i will suspect the harness itself allow the CDI to deal with igniting the coils directly without some sort of diode assist / or igniters.

Since fitting new coils ….   These would also cut sparks off  (and i will also assume they have been checked already ?)
– > Clutch Handlebar switch  (bypass it, because it’s a race bike, you won’t need it unless your local club says it must be present)
– > Kick Stand switch  (bypass it)
– > PickUp Sensor from the Stator  (but it works as its circuit isnt dead and is in good ohms spec)
– > CDI unit.
-> Regulator Unit   (You can contact some local wreckers and ask for a Kawasaki Mule regulator and a genuine  Yamaha r1 regulator. Please avoid knockoffs because it’s not fun to see regs in smoke – its so common usually electrical issues we tend to only blame the coils, reg and stators because Hyosung doesn’t make them , but they are outsourced parts  to some other korean company to do it.  I digress, sorry.

Here is another hint,  if you have a Digital Dash connected to the harness, you will see the rpm counter bounce when its cranking –  That confirms it magneto is spinning 600 rpm as the typical speed of the stator motor to crank a heavy 250 flywheel.

I know you said the harness is checked from end to end with a meter, every wire colour you can find matching, so that’s great. I “should” assume the harness is okay , i can’t see it being fried from the pics or toasted up.

Perharps a spare harness from the wreckers and swap over the diode sensors and try again also ?

Keep us posted please.  This is interesting.

[Simon]

That yellow thing with the diodes connected looks like a safety capacitor of some sort.

[Hyo71]

SOLVED!!

I put a stupidly low bid on a crash damaged 2008 GT250R on NZ’s equivalent version of ebay and somehow won the auction! I bought the bike back last night and swapped the CDI, and bingo! Spark against the cylinder.

The engine I put in was from a wrecker, so I still wasn’t entirely sure if there were any issues with it. After probably 20 attempts on the starter and a heap of fiddling with the choke slide by hand (the carb isn’t hooked up to cables or airbox), she fired a little burp. From here it took another few minutes of trying and she finally started and ran.

Still not sure what the yellow thing does. It is odd that it isn’t noted on the wiring diagram.

When testing the wires and looking at the wiring diagram, it seems the CDI deals with igniting the coils directly as well as sending signal to the tacho. Is this signal what tells the tacho what revs you are doing or does that come from the magneto signal?

That hint on the tacho and magneto is a good one, I’ll have to remember that for next time.

Yep, I think the black wires are for a horn as well.

Your assumptions are correct Marcel, the clutch, side stand and pick up sensor were some of first things I checked off when I started. The regulator rectifier I still felt wouldnt cause a non spark event so I left that off my list for the time being. The CDI was definitley on the list of things to try but it was the out of spec resistance readings on the secondary’s on the coils that led me to belive the coils were the culprit. Spec states the secondary’s should be 5.4 – 6.6 Kohm but I was getting around 14 Kohm. When I tried the replacement coils and they failed, I checked them, and they also tested to around 14 Kohm. Whether that has an effect on performance at the upper end of the rev range, I’m not sure, but I’ll find out.

Now I can progress putting this bike back together..

 

 

[Hyo71]

Looking into this yellow thing a bit more… Since I’m getting continuity from the yellow thing to the horn plugs, it makes me think it has something to do with the horn. Doing a random ‘bike horn capacitor’ google search, I think it might be a ‘3-pin alarm boost inductor’ for the horn.

It’s a little hard to see in my photo earlier in the thread with the yellow thing circled, but I think the diodes are orientated in the direction of one ‘in’, and one ‘out’. Im thinking that the ‘in’ diode would allow a signal from the CDI to come ‘in’ and prevent a ‘boosted’ signal heading back to the CDI and blowing it. The ‘boosted’ signal would then go through the ‘out’ diode to the horn – I’m no electrician, this is just my loose understanding of diodes.

When I’m next in the shed, I’ll take the horn off my new “parts bike” plug it into the black plugs and see what happens when I unplug the yellow thing from its connector.

[♠️ M77]

Hey,

I am very happy for you that the bike finally ran, i did think the CDI was sort of the last resort item for sparking woes, now if anyone has similar woes, i will make sure to make them digest this topic.   Very informative!   Hell, you even laid out you tested some electrical components and what the specs are.

Usually some folk can’t or won’t want to read the manuals if it is too confusing for them ,  but not always!

I’m quite jealous you won a cheap auction backup bike but that will come in handy as parts donor for your racing days, you won’t have to wait to replace anything or just have an extra girl ready to go!  A little switcheroo won’t hurt haha.

As for the harness, if the ignition system has to pulse 10,000v to spark the plugs, i would not be surprised if the koreans added one way diodes or some other mystery sensors embedded in the harness so that things don’t retrograde back if something doesn’t go to plan.

The horn does draw some power to be fair and it’s always live  (as long as engine is running) , so all the rider does is press the horn button to complete the circuit.     You don’t have to be a full electrician right now to know sometimes bad coils will arc the sparks or zap signals out of their HT leads , the harness must not get fried back or the cdi.  It isn’t fool proof since the stator unit can still blow the cdi or blow ignition system system.

Just make sure it produces 70v around 5k revs and never exceeds 90v in any revs ,  it is almost the hottest thing on the left side of the lower crank.

When starting the bike -> magneto tells cdi how fast the rotor is spinning -> the CDI then tells the dash board (rpm signal bouncing around 600 rpm) , now the cdi next has to communicate with the rest of the ignition system to spark the plugs  (as long the clutch switch & kick stand doesn’t prevent the CDI from doing so – – ie. safety cut out — (ie to avoid setting off with the stand down   or starting the bike without holding clutch)

Neutral sensor isn’t foolproof , it may say N but gearbox may still be “slightly engaged” , alas when bike starts , it rolls 3 seconds later and falls , oh yes , i’ve witnessed it haha.   I always make sure to roll the bike forward and back anyways to make sure its really neutral , keep gear linkages greased up and sparing no expensive on quality oils.  That will keep the valve train silky smooth  (oh yeah, the engine doesn’t have a camshaft under the gearbox too)

[Hyo71]

Hey,

Yep, rediculously lucky with the auction. Once I get this back-up race bike ready, I’ll probably turn my attention to the new parts bike and see if I can get a 3rd race bike out of it – could start a little race team haha.

I tried the horn, and it’s as you described – the yellow brick thing made no difference to the horn. The bike also continued to run at an idle when I disconnected it – there was no effect on the running bike what so ever. I didn’t think to see if the bike would start with it disconnected.

In the video you can hear the bike about to die when I try rev it up but I release the throttle just before it cuts out. The bike starts easily now and once warm I try rev it up,  but it still trys to die out. I’ll have to check the stator output next like you mentioned above to see if its cutting out when the revs rise – maybe the rectificer is toast. Will have to try the one on the parts bike to see if there is a difference.

Could it be the fact that I dont have an air filter on it? Would that cause it to run lean and die out? I’ve got a busy month ahead, so probably wont touch it for a while – probably start a new thread when I get back to it.

Thanks for the support on this spark issue, hopefully helps others.

 

[Cobra2]

What is missing from the manual…the correct pin-out for CDi, with correct wiring-colors…

Just quick-tested my wiring, and found that the BROWN wire had 0-ohm to gnd/chassi with support up, infinite, with support down. Clutch-switch also had an impact.

Could not get a reasonable reading thru pickup, shows several M-ohm ???(Green to Blue), (Green to gnd ~100 ohm…) ?
(Runs OK) !

Arne K
2017 GT-R-125

Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).

GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂

[Cobra2]

CDi pin-out, as far as my wiring-diagram compares to my bike…:

Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).

GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂

[♠️ M77]

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

[Dariel]

Hey guys, I’m from Brazil and I have a hyosung 250 and I’m having problems with its CDI, I’m not trying to get a spark in the cylinders, I’ve already changed the CDI, coils, spark plugs and spark plug wires and it’s not resolved, could anyone give me some help???
I already did the same tests mentioned above and got no results.

[♠️ M77]

Dariel wrote:

Hey guys, I’m from Brazil and I have a hyosung 250 and I’m having problems with its CDI, I’m not trying to get a spark in the cylinders, I’ve already changed the CDI, coils, spark plugs and spark plug wires and it’s not resolved, could anyone give me some help??? I already did the same tests mentioned above and got no results.

Quote

See my latest reply on this topic below:

No spark on one side

If you still get problems => Post a new topic for yourself and tell us everything you did.

Good luck!

[Author]

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