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DT 125 lc -87 spark missing

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So Once again the old bugger failed me.

Dt had something fishy with the wiring. It sometimes hardly had the juice to go through the ypvs check procedure. The servo worked really slowly. Yet straight after it could have worked like it should. The low curret could be seen from very dim light on the neutral indicator. So when the fail was on the light was dim or did not glow at all.

This short affected the ypvs when riding the bike. Sometimes it did not open the exhaust port at all.

I did a bit of work with the wiring (again) and the problem seemed to go away.

But: this morning I took the bike for a ride. It did cut the ignition few times on high revs. After a short pause it did not start at all. Checked the spark and there wasn't any. So I had to fetch the bike back to base with a van.

I took apart the wiring, replaced some fishy connectors with good old soldering finally the spark returned. a very WEAK spark but still a spark. The bike started like it should and so off to the road...

It worked really nice the ypvs worked like it should and going was good. Until... It decided that I'm far enough from home and just died or ran out of sparks so to say.

After a half an hour cooling it did a short promise but I still had to fetch the van.'

What on earth could cause this? The plug should be good. I checked the wiring including cut off and magneto and all that. Is it about the battery or could it be that the cdi is about to fail and does just that when the temp rises.

Anyway, I'm getting a new battery tomorrow. Doubt it helps.

By the way. If any of you wonderful people are millionars and want to help a bloke out a new yamaha would be nice. Summer is short here in Finland and riding is lot more fun than fixing :eusa_angel:

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If it starts again after cooling down you need to check the pick-up coil and ignition coil when hot right when it dies and if it passes then it might verry well be the CDI it is very rare that they go that way and up till reciently I though I was the only person who ever had that happen but Tommy has informed me that he too had it happen .So this will be the 3rd time if it is the problem I have seen/heard this happen.

so pack some tools and a DVOM and go for a ride aroud home area and wait till it does it and check it right away,a can of compressed air can cool the cdi down quickly and if it starts then you found the problem.

My rz would just up and die ,,waite a hour and bang it would run again,some times for days,other times it wouldn't start then after kicking it over 50x or more it would and run as if nothing was wrong.

Report back with what you find.

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Could not.

This time no spark at all. Time to check the resistance of the coils at room temp. HT coil should be good as it's new.

Oh and I tried to get a spark with two new plugs, so it cant be the plug. Too bad none of my friends have a dt anymore. Cant borrow a cdi to test.

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Oops I'm really shi++y with electronics. Can anyone tell me what to measure. I have 6 leads coming from the front of the magneto: Yellow/red


Light blue




First three on same connector

then the two on same connector

And the lonely black/red

What should I measure and from where?

I took a reading from the connector on black-brown and it was 09.4 at 200 ohm scale

The pulse coil leads are easy. white/red and white/green on same connector.

And by the way. There's and indian cheap cdi on ebay. It says it fits dt125 and dt175. No years or makes specified. Opinion on that?

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How? Did you find the problem?

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Err well I was perhaps a bit too optimistic yesterday. It generates a spark now. A weak one but it hasnt been a big flash to begin with.

Anyway, with furious kicking and changing the plug, as it got wet right away, and few downhill starts it finally came alive.

Same procedure this evening. I drove around the yard far a while and then it just died. Plug was wet again. But this time it still managed to create the shy spark with a dry plug.

Conclusion: As the weather is really hot now here in Finland at shadow some 32C and the bike is set to be at rich side with 1/4 to 3/4 throttle at about 15C so it might just now be too rich to even start. Or it might be still fault at the CantDeliverIgniotion unit. I shall adjust the needle one notch lower tomorrow and see what it does then. Might be worthwile to check the reeds while I'm at it.

I sure wish I knew for sure...

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It wasn't that :icon_frown: It just dies after a short run.

I couldn't find resistance reading for the ignition coil(the one inside the magneto) from Haynes. It just tells the values for light coil and charging coil.

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Hi, and merry christmas everyone.

I'm back with this old thread once again. I bought a sparepart bike from a dude that blew the tranny from his similar dt during summer. I took most of the electric stuff off from the wreck and bolted them on my sorry old green piece of ....

So the CDI, ignition control, stator and flywheel are from the spare bike.

I din't ride the bike for a while since I thought that the mainbearings were so busted that the magnetoside seal wore out wery fast. There was conciderable slack on the bearing when jerking the flywheel up and down. All the running problems seeemed to come from a serious air leak.

So few weeks back I took the trouble to overhaul the engine. Replaced all bearings and seals.

The machine seemed to run ok. Then all the sudden the fault returned. Tried on another carb. Still the same. So it had to be electrical. It might run great for a while then all the sudden it starts to sort of miss a spark splutter and die and after that it's wery hard to get running.

Well since that DT is kinda precious to me I replaced the one possible source of trouble the ignition lock with a switch. Even made a very cool text on the plate that holds the switch. Instead of just reading plainly "on" and " off" It reads "OFFLINE" and "ARMED" (the bike is coloured olive green hence the text.)

And after all that loving care the piece of s... still had the nerve to die on me and my 5 year old son just as we were toving his stiga sledge. SHAME!

Now I concider my self as well tempered man but still the image of me jumping on the bike and setting it to fire was for a moment very vivid.

Well. since I'm not a quitting type I took the one electric component from the sparebike, that being the ypvs servo and fitted it today.

Didn't try it out. Day of reconing will be day after tomorrow. If it still wont work I really dont know what to do.

Oh, I could tow the little guy with the KTM but it sounds bit scary =)

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Hi mikko" I would start replacing from the cheapest item first, - spark plug - coil - ignition pick up. then maybe the earths,

I can"t see both cdi units being faulty,

Even try trim 10mm of the present HT lead,,,, :yeah:

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