ignition trouble...what to do?

[scout127]

I've got an '83 GS850L. I'm getting a very soft spark from my plugs. The plugs are new and produce a great spark when checked on my friends bike. I'm getting 11.5 volts at the coils on three posts. On the white wire (firing the 1 and 4 cylinders) I'm only getting 1.08 volts. When I disconnect the wires from the coils, I get 12 volts between coils posts (I assume this means the coils are good). I've checked the resistance through the white wire from it's connection at the CDI to the coil. It is fine...no break or grounding out there.

When I reconnect the CDI, the voltage drops back to 1.08. I recently replaced the CDI with a used salvage one. On either of the two boxes (my old one and the 'new' salvage one) I'm getting the same readings.

What does this indicate? Should I be getting a solid 12 volts at the coils?

I know this is a lot of information...I hope it's not too confusing. I'll appreciate any help!

[scout127]

I should mention that before testing the coils, my battery read 12.7 volts. this means that I lost an entire volt from battery to coils. Not sure if this is normal or indicates a problem.

[BassCliff]

Hi Mr. scout127,

Here's a few suggestions...

The Stator Papers - There's a troubleshooting section.

The Coil Relay Modification

Maybe new plug caps? Or perhaps you can just cut off a quarter inch from your existing plug wires and reconnect your plug caps into some fresh wire. Sometimes the very ends of the wire can get a little corroded and build up resistance. Also, clean every electrical connection and ground, from the headlight bucket to the tail light. Run a dedicated ground wire from your r/r directly to the negative terminal of the battery. Keep us informed.


Thank you for your indulgence,

BassCliff

[rustybronco]

I'm getting 11.5 volts at the coils on three posts. On the white wire (firing the 1 and 4 cylinders) I'm only getting 1.08 volts. When I disconnect the wires from the coils, I get 12 volts between coils posts (I assume this means the coils are good). I've checked the resistance through the white wire from it's connection at the CDI to the coil. It is fine...no break or grounding out there.

what do you mean by, between coil posts? there are three of them on each coil.

What does this indicate? Should I be getting a solid 12 volts at the coils?

you should be at or very near battery voltage at the battery side of the coils.

the way the system works is, voltage is applied to each coil. the ignition module grounds the coil required (just before it is about to fire), causing it to build up a magnetic field in the primary side of the coil. when the coil is needed to fire, the ground is removed from the coil, causing the magnetic field to collapse and inducing a voltage on the secondary side of the coil (the coil is a step-up voltage transformer) which travels out the coil wire, through the plug cap (a resistor for noise suppression). finally it will jump across the electrode to earth (ground).

when the coil is building up it's energy, you will show battery voltage at the positive side of the coil and near zero volts (it could be 1.08 volts, I've not measured it) on the negative side of the coil.

when the coil has it's negative (ground) removed, you will read battery voltage on BOTH the positive and negative sides of the coil (remember, the coil primary and secondary's are nothing but long wires, wound up)

did this answer your question(s) y/n?

(we won't get into electrons have a negative charge )

[scout127]

when the coil is building up it's energy, you will show battery voltage at the positive side of the coil and near zero volts (it could be 1.08 volts, I've not measured it) on the negative side of the coil.

If this is what I'm experiencing, wouldn't turning over the engine cause a change in voltage reading? I can't remember if I turned the engine between reading.

when the coil has it's negative (ground) removed, you will read battery voltage on BOTH the positive and negative sides of the coil

This is what I meant by "between the coils". This is what I did and assumed it meant my coils are good.

[rustybronco]

If this is what I'm experiencing, wouldn't turning over the engine cause a change in voltage reading? I can't remember if I turned the engine between reading.

While cranking, you will see the ground side of the coils "alternate" between near battery voltage and around zero volts, if your meter reads fast enough.