[brtrx]

I've opened up my crank case and found 2 pulse / stator coils, about 160 degrees apart. (PC1 and PC2 on the wiring diagram)

One of them is dead (30M ohms, instead of 350), but no-one in the shed seems to understand why there are two at an angle to each other.

Specifically, we want to know whether there's some redundancy here, which would mean the CDI should still be driving the ignition coils correctly, even if one isn't working.

The CDI is suspect, but obviously I don't want to replace the CDI unless I have to, so I want to rule out the pulse coils first.

I would just replace the coils, but I haven't found any yet, if anyone has a tip on where to look, I'd appreciate help with that too. I haven't even pinned down the exact part number yet.

 

[LaCarolus]

Are you talking about one with a seven "pronge" pulse rotor?

 

[brtrx]

I think it has eight prongs.

I'll attach photos of the inside of the crank case cover and the rotor sprocket, in case that helps.

 

[brtrx]

Photos

Photos of crank case cover and rotor attached

 

[LaCarolus]

It's my understanding that one pulse coil controls #1/#4 and the other controls #2/#3. It does require both to work correctly...no redundancy there . What has led you to believe that the CDI is bad? If you know you have suspect reading from you pulse coil why not just replace it?

 

[LaCarolus]

If you are having trouble finding replacements you might try calling electrexworld.com. They manufacture ALOT of motorcycle stuff and even if they don't have a direct replacement for you they might be able to send you in a better direction(they also offer a repair service for some ignition parts). You mention that the CDI is suspect-What was happening that made you look at the ignition system in the first place?

 

[brtrx]

Thanks, LaCarolus.

We started looking at the ignition system, because we weren't getting any sparks, even with fresh plugs.

I also thought that each pulse coil triggers a separate pair of ignition coils. What's weird about that theory is that the pairs of pistons should be 180 degrees out of phase, but the pulse coils are set at about 160 degrees. And why then have two pulse coils at all? Wouldn't one be enough (with a wasted spark on the exhaust stroke)?

Forgive me if this seems very academic. Obviously, I'm using this to learn a bit about how the bike works.

Thanks heaps for pointing me to the electrexworld.com site. I found a replacement coil in 2 seconds! (I also learned that they're also called "pick-up coils", which - for a guitarist - makes perfect sense!)

 

[brtrx]

Well, I spoke too soon about the parts (they only have CB250 pick ups).

But I did find an explanation of the two pulse coils (although I admit I don't fully understand it):

A pulse has seven projections. From (1) to (7) have 45 degree separation and 90 degree for (7) to (1). The engine rpm and crank position for each cylinder are detected from the relative position of the seven projections and two pulser coils. The two pulser coils are installed so as to have 15 degree inclination from level line for PC2 end, compared to PC1. This angular offset is to detect crank positions.

Cbr250r Pickup Spark

There's also a good ignition system diagram (but no wire colours!)

Oh, and you were right about the number of prongs (embarassingly for me).