Bike has lost its spark

[tomf]

Well my bike was running the other day, but when i went to sort out a non idling problem with it i had it running for about 5 minutes then it just died and wouldnt start.

The bike is a Lifan GY125 it doesnt have any road electrics fitted, so there is no battery, just the kick start.

So i took the plug out and found i want getting a spark, so i a new spark plug and was still not getting a spark.

So i tested both the wires that feed the coil and i was getting 12v when i kick the bike over and the other doesnt read, so i presume an earth. These are the sort of reading that i would have expected.

I then thought i would check with the multi-meter at the end of the HT lead and found that i was only getting 12v there insteasd of the roughtly 120000v you would expect.

Now im new to bikes but on a car iv not experienced a coil just completely fail they usually brake down over time, also i can understand if the coil was broken then why is there any voltage atall at the ht lead?

Is there anything else i should be looking at that will still feed the coil with 12v but cause these problems?

[mr rip]

you'll probably find that your meter won't react fast enough to read a voltage coming from the ht lead as it's little more than controlled lightning bolt

your best bet would be to disconnect the coil & do a ressitance check on it (if you can find out what the readings are ment to be)

the spark is created by shutting of the power to the primary windings which collapses the magnetic field & induces a voltage in the secondary windings which travels to earth via the spark plug

your generator coils sound like they are working ok,

you should have a little signal sensor/sender unit in or around your magneto which sends a signal to your cdi unit which in turn does what it does to the coil any one of these three items could be at fault or the wires in between them

so you will need to test these to find where tha fault lies
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never criticise a man until you've walked a mile in his shoes, then when the muck hits the fan you'll be a mile away & you'll have his shoes

[mr rip]

if you can get a 12v battery from somewhere it would be easy to test your coil in a more flamboyant maner

conect the negative lead of the coil & the battery to the frame

put your new plug in the ht cap & rest it on the cylinder head

then touch a positive lead from the battery to the positive lead of the coil when you pull it back off the lead there should be a spark at the plug

if there isn't then your coil is duff, if there is then it's working fine
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never criticise a man until you've walked a mile in his shoes, then when the muck hits the fan you'll be a mile away & you'll have his shoes

[tomf]

Thanks for the reply yes if i was getting the correct HT lead voltage i agree it would read correctly, but when i conect one voltmeter up to the end of the HT head and another voltmeter up to the coil power feed and kick the bike over i get exactly the same readings.

If there was a problem with the magneto sensor or the cdi unit is it possible for the coil to still be getting a 12v feed?

I did suspect the wiring being a problem as the bike cut out when i put the seat back on and road it down the track, but i have checked all the wiring with a continuity tester and they all show to have continuity.

[tomf]

Sorry me being slow, ill do a test for the coil now.

Thank you for the help, really appriciate it.

[ZRX61]

I have a half bag of sparks left over from some grinding I did yesterday, I could send you some...

[mr rip]

the natural state for the coil is to have a charge going to it, the spark is produced when the power is cut off, either buy the points opening on an old system, or buy the the censor in the magneto sending a signal to the cdi unit to cut the power off at the correct time

test the coil with a battery the way I mentioned above, it should give you a better idea of where to look if that isn't the problem
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never criticise a man until you've walked a mile in his shoes, then when the muck hits the fan you'll be a mile away & you'll have his shoes

[tomf]

cheers mr rip.

Iv just tested the coil on my car battery they way you said and there isnt a spark, i did notice the coil got very hot quickly though.

I had the earth terminal negative on the battery, i put the plug on the block (attatched to the ht lead obviously) then touched the other terminal onto the live and removed it.

I did notice when i touched the live wire on the battery there was a small spart where the wire met the live terminal so is this shorting out accross the coil?

[mr rip]

did you have the negative lead conected to the frame aswell as the the coil?

if not then the HT lead would have had no earth & wouldn't have sparked anyway

dont worry about the spark as you touched the positive lead to it, you were just completing the circet & a car battery has a lot higher amps that the bike battery would, that's why it got a bit hot

the coil is the easiest part to test so if thats the problem then it saves some headaches

these guys seem to have a good selection of parts for those aswell as new coils for 28quid

https://www.google.co.uk/aclk?sa=L&ai=Cqx3ZZUouTOW4CM7UOLSsqe0Bjq7giAGm9tayEaGBucYWCAAQASDHmPgFKAJQurmz_Adgu-6Xg9AKkAECyAEBqQL8XCfMeHa5PqoEFk_QjYrE1QL93RE-8n5J6c4laiUPaz2ABZBO&sig=AGiWqtyLcczbP2MCg0O0K7qlTDxVZAEoEQ&adurl=https://www.china-parts.co.uk/
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never criticise a man until you've walked a mile in his shoes, then when the muck hits the fan you'll be a mile away & you'll have his shoes

[tomf]

Yes i tested it on my car battery with it still fitted so when i said i put the spark pulg on the block i meant the car block, so is already earthed as i left the battery in situ.

The coil did get very hot thought, like to hot to hold in my hand.

Thanks for the link ill order up a new coil i think as for that money even if it does turn out to be something else i havent really lost to much.

It the coil doesnt solve the problem do you know how i test the cdi unit and magneto sensor?

[mr rip]

ok, well I had ment for you to test the coil with it still bolted to the bike frame as the metal bar that runs through it can be part of the circet (although, not always)

coils do get quite hot at times & a car battery is a lot higher powered than a bike one that's why I said to just touch the positive lead on it & watch for a spark when you pull it off

with out a circet diagram listing the correct readings you would expect to see, I couldn't tell you how to check the other parts

most manuals suggest you just do a straight swap for a part that is known to be working as the best way to check them
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never criticise a man until you've walked a mile in his shoes, then when the muck hits the fan you'll be a mile away & you'll have his shoes

[Ariel Badger]

Clean the points in the CB. If the bike had sparked it would have cooked your multimeter btw, do not put big volts through them.
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Bikers make great organ donors, get 115 on your licence today.

[Pete.]

[mr rip]

no, it's not a resistor, it's just a piece of wire & although it has some small amount of resistance it will keep letting power through it until the point where it burns out

there is a big difference between the amount of power the coil can take before it burns out & the amount supplied to it by the battery & the more you give it the faster it will heat up
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never criticise a man until you've walked a mile in his shoes, then when the muck hits the fan you'll be a mile away & you'll have his shoes

[Pete.]

Actually it is exactly a resistor but the biggest part of my point is that the coil will not heat up more simply because a car battery is used over a bike one, unless the bike one was too small or flat and incapable of powering the coil sufficiently. Your previous post inferred that using the car battery caused the coil to heat up more because it has more amps, that's not true.

Too many people already think that using a car battery to power bike electrics might cause damage because the car battery is larger, the reason I corrected you is to help prevent perpetuating that misunderstanding. Car batteries can be used to replace bike batteries, without changing the operation of the bike's sytems.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[mr rip]

well you are partially correct

a car battery can be used on a motor bike to great effect in a lot of cases as the voltage & current are controlled by several other componants before it gets to the main systems

but in this instance it wouldn't have been, it was just the coil on to a battery,

the coil is just a long piece of wire it will allow as much current through it as you can give it upto the point where it melts & breaks the circet in the same way that a fuse does,

if you connect it up direct to a battery you are just creating a short circet

if you short a piece of wire across any battery it will get hot & the higher powered the battery the hotter it will get & the faster it will get hot

the coil has resistance but it isn't a resistor, a resistor only allows a set amount of current to flow through it

I'm sorry if this concept is beyond your grasp but that doesn't make it wrong
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never criticise a man until you've walked a mile in his shoes, then when the muck hits the fan you'll be a mile away & you'll have his shoes

[Pete.]

[mr rip]

that was sarcastic & uncalled for, & for that I am sorry

as far as reading up on what I'm talking about goes I am a trained mechanic with more than 20 years experience & although I am now retired I spent the last 5 years of my working life as a coil winder & tester in the electric motor industry

I don't really need to do any more reading

the battery on 90% of modern motorcycles runs in parallel with the voltage regulator & only supplies voltage to the system when the bike is idling or the engine is not running, the only part that gets direct battery power is the starter motor & take a look at the gage of cable they use for that

all metalic substances have resistance, I am not trying to dispute that but there is a difference between resistance & a resistor

copper is a conductor & will burn out befor it gets to a point that it can't let any more current get through it

the coil is wound with a specified gage of wire for a specified number of turns calculated using the intended power that is going to be put through it, if you put more power through it than was intended then it will heat up, I am sorry but that is 100% fact
what I am trying to point out is that the car battery puts out more than the intended power for that coil

& as you point out the resistance goes up as the temprature increases, that increases the rate that the coil heats up

try putting a car coil onto a motorbike & see how much of a spark you get out of it it'll run but it won't be very happy

again I am sory if I offended you with my earlier coment

but I think we are going to have to agree to dissagree on this one
as this squabling isn't going to help th OP get his bike fixed
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never criticise a man until you've walked a mile in his shoes, then when the muck hits the fan you'll be a mile away & you'll have his shoes

[faceache]

I remember on points ignition bikes we never used to leave the ignition on due to the fact that if the contact breakers were closed there is a permanent supply going to the +ve side of the coil which could result in overheating and frying said coil.If youve held the +ve terminal of the coil (while -ve is earthed to same power source) for a length of time coil could be shag@ed . Best just to tap tap the +ve term on battery +ve and see what happens. A direct connection to a battery designed to turn over an engine will pass more current thats why we have fat starter motor leads.Wack a cheap coil on it and see what happens if its not cured youve got a spare coil .Or am i just waffling (it is past my bedtime and ive mainlined some coacoa)
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surfing synewaves the bad makes the good even better

[tomf]

[faceache]

if your coil isnt nacked youve either got an ac pickup coil 2 wires coming out and sends out ac power to test it connect your multimeter probes to the ac pickup wires (with multimeter set ac volts on a low setting) and see if it puts out power .Ive read its supposed to be .5-3volts but ive had a lot more out of them(14v) and it depends how fast you are cranking.or you could have a hall effect pick up which is a little magnet with a wire coming from it and it picks up gaps as the plate on the shaft spins past it as opposed to th ac pick ups having magnets spin past them. Stick +ve probe of multimeter on the wire coming from the sensor and the -ve to earth and crank and you should get alittle signal voltage sent to the black box.As for testing black box the best way is elimination.If you know the coil is ok and you know the pick up coils are doing their job and all the wires have continuity and the ht lead is good the plug cap has the right resistance and the plug is good .then its cdi shagged.Hope this helps if any of its wrong and you blow your bike up remember that i told you i got fired from atleast 2 of my jobs in the bike trade. But i always liked electrics for some reason.And you know what i ididnt even have to write all this down cos you didnt even ask, i couldve sworn you did ,i think i need to go to bed.
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surfing synewaves the bad makes the good even better

[tomf]

Well the coil got delivered today, stuck it on the bike, did it didnt make any difference

As far as i can work out the magneto sensor has 5 wires coming off it. Two of which go to a plug that is not being used (this was how it was before when i was getting a spark, i pressure its because its had most of the electric removed as its not used on the road anymore)

So that leaves 3 wires, one goes to an earth and the other two go to the CD0 unit, i cant remember what wires i tested as i tested loads, but there was definitely a voltage of about 12v coming up one of the wires from the magneto sensor to the CDi unit, i cant remember what the other wire gave if anything.

Is this was i should be expecting.

Im finding it a bit difficult to find a matching CDi unit to my one.

I did try to have a look at the magneto sensor but i only got as far as removing the chain gard to find that is was mounted internally to the engine, which was full of oil being a 4 stroke, so would prefer to try and work out what reading im supposed to be getting on the multi-meter before i strip that apart.

[tomf]

Well i finally got to have a little look at the bike today.

The magneto sensor has 5 wires coming off it, two of which arent used.

One of the wires is an earth
The other two go to the CDI unit.

I checked the voltages of these wires, obviously they changed depending on how hard i kicked the bike over but one wire would read up to 80+ volts, but the other wire would not read much 0.2 volts max.

Does this sound correct?

[stirlinggaz]

hi,
i have no idea what your issue is, so cant help there but i do have a spare CDI that im pretty sure was fitted to a gy125.
its a red racing version (but doesnt give any improvement over the oem one)
i was given it to test as its a generic cdi & on some bikes removes the rev limiter.
ifd you want it, give me a shout,
cheersd,
GAZ

[tomf]

How much are you after?