Weak spark, or no spark

[Haako Smith]

I was out riding the other day, then suddenly my bike started to bog down when I gave it full throttle. Ran ok at idle, but when I tried to start it again it didn’t fire. I checked the plug on another bike and it was fine, tried another plug wire and plug cap. Then I sometimes had spark, but very weak spark. And it seems to come and go.
Anyone have any idea?

[Calum]

I've had this before.

Bad grounding, lose wires and deteriorated connectors can cause this.

Also check the HT Coil and measure its impedance and check it against the manual to see if it's within tolerance.

[Haako Smith]

Thanks for responding.
I managed to get I started, but only for a couple of seconds. I felt like it was the same as yesterday. If I gave it some throttle it died. I had a random coil laying round and I checked if it was a difference, but it was the same. Sometimes weak spark.
Should I measure the ohms in the coil?

My bike is a Yamaha dtr 125 2002

[SpookDog]

If it’s not the coil. I’d start working through the rest of the ignition wiring and parts. Key barrel, kill switch, sidestand switch, sidestand relay (if applicable) the pulse generator/ pick up, stator coil, ect, ect...

[Calum]

I had the ignition barrel connector block just crap out on me and that was giving me grief.

[Haako Smith]

Hmm. I measured the resistance between the coil, as you can see in the picture. In the manual i have, it says it shold have somewhere around 7,5K. Does my coil seem ok?

[Haako Smith]

My coil measures to 8.05K

[Haako Smith]

I tested the resistance in the pickup coil, and it showed 300 ohm. The manual says that it should have 9-11 ohm

[Haako Smith]

It has spark before the spark plug cap, but not after. ( sometimes it has)
And it’s not the cap that’s bad, I have tested it.
So it basically don’t have enough spark to fire.
So I’m thinking it’s the coil maybe??
Anyone else thinks so to?

[oldman]

My bike refused to start Sunday, tested coil (non original) and no resistance on secondary coil, swapped it for spare genuine coil expecting fix but still no spark. Checked side stand switch that was ok, checked kill switch and duff connection. Fixed that and all good. When bike was rebuilt a couple of years ago had intermittent fault where bike cut out, traced that to poor earth (corroded in loom) around coil area . Ran a new earth from there direct to battery. If you find my rebuild thread it's described in there, removed loom and tested resistance of cables and found it.

[Calum]

It would appear as these bikes starts to age the looms are becoming susceptible to failure.

[SpookDog]

@Haako-Smith said in Weak spark, or no spark:

I tested the resistance in the pickup coil, and it showed 300 ohm. The manual says that it should have 9-11 ohm

Well if that’s right then there’s way too much resistance. Resistance cuts down the amount of power flowing through.

I’ve got an old shitty looking one that I know works. You might have to bodge the connectors for your bike.

If you’re UK side you can bung me a few quid for postage and it’s yours. I wouldn’t use it full time without waterproof/mending the grommet

[Haako Smith]

hmm, i checked the stator aswell, and i measured that 12 volts is coming to the cdi, but only 6 volt at max is going to the coil, from the cdi. So im kinda thinking its the cdi maybe. But the resistance should not be 300 ohms at the pickup coil? Could that maybe be the cause? Im in Norway btw, so not exaclty close xD

[SpookDog]

Sorry, but I’m not even going to try postage to . Try and find a different pick up to try. It sounds like a suspect...