Yamaha XJ650 ignition plate pickup coils replacement

Hi everyone,

I'm working on troubleshooting a classic ignition issue on my 1981 Yamaha XJ650 midnight Maxim (non-YICS engine). I traced a dropped spark on cylinders 1 and 4 down to the timing plate, and my multimeter confirmed my worst fears.

Testing the original pickup coil assembly with the ignition OFF and the TCI box completely disconnected, here are my resistance readings directly at the harness wires:

• Orange to Black circuit: Healthy at .643 ohms
  
  
• Grey to Black circuit: Dead O.L (Open Loop)

Clearly, the internal winding on the 1/4 pickup loop has snapped inside the factory epoxy molding.

Here is my dilemma: My original factory baseplate is stamped PU212-01. I’m having a tough time finding an exact matching used unit online right now, but I have come across a couple of other vintage Yamaha assemblies stamped PU212-06 and PU212-04.

Visually, the plates look almost identical, but I know how precise these 80s metric ignition systems are.

1. Can I safely use a PU212-06 or a PU212-04 baseplate on a standard '81 xj650 Maxim engine, or will the mechanical timing advance curve/degree angles be completely wrong?
   
   
2. Are there any other specific dash-number variants (or plates from other XJ models like the 750) that are a direct, verified plug-and-play swap for the PU212-01?

I really want to get this bike back to firing on all 4 cylinders. Any wisdom or interchangeability advice from the XJ gurus would be greatly appreciated!

Thanks in advance,

 

Unknown, but the "suffix" (-01, -02, -03) are typically different for each engine. Unless you have the other baseplates and the original one all lined up in front of you, it's pretty much impossible to tell whether there are any significant differences.

We do have some good used coils available for the 1980-81 XJ650 models. You can contact us thru this website or e-mail us at: info@xj4ever.com

But.....the pick-up COILS are just attached to the baseplate with small screws, so the actual coils can be detached from the baseplate......so all you really need are the coils (instead of the entire baseplate/coils system).

 

Thanks for the feedback, are the pickup coils interchangeable? I have one donor pickup coil assembly that has a good and a bad coil.

On the donor, can I remove the pickup coil trigger that is good and swap it with the one that is dead on my bike? I know that some wire soldering will be required.

 

Yes, you can swap a single coil (or both coil packs). Just be aware that there are different specs for pu coils, here's the roadmap:

120 ohms +/- 10% (XJ650 T,urbo XJ700 air-cooled, XJ750RL Australia, XJ900RK/RL, XJ1100 )
650 ohms +/- 20% (XJ550 all, 1982-83 XJ650"yics", XJ650RJC yics, XJ750 Seca, XJ750 Maxim)
700 ohms +/- 20% (1980-81 XJ650 "non-yics", XJ650RJ Seca "non yics")

So you need a donor coil(s) that are 700-ohms resistance, which means from a 1980-81 XJ650 or a 1982 XJ650RJ Seca (non-yics model.....the XJ650RJC models (the red bikes) used the 650-ohm coils as they are YICS engines.....).

Now, you might ask: what difference does it make between a 650-ohm coil (+/- 20% = 520 to 780 ohms range) and a 700-ohm coils (= 560 to 840 ohms range) since there is a rather large range of overlap of "acceptable" resistance specs? I think (but am not sure, since there are no published specs......user @Rooster53 can comment more intelligently on this matter than I ever could!) that there is a difference in the voltage output of the two different types of p/u coils, which in turn is necessary for the TCI to interpret the signal correctly.

ALSO......some p/u coils versions only use a single ground wire (both p/u coils share a common (black) ground wire) whereas the 650-ohm versions have individual ground wires for each coil. This affects the pin-out on the 6-place plastic shell that attaches into the TCI.

Finally, some TCI's (the ones that are used on bikes with a sidestand safety relay) have an extra "grounding" wire coming out of that 6-place connector) that serves to shunt the TCI output when the sidestand relay is "active" (meaning, the sidestand is in the down position). Your bike should not have a sidestand relay / safety system.

 

Thanks Chacal! That clears things up.
I’ll swap a trigger coil from donor to my pickup coil assembly on my bike. As soon as I get the job done I’ll post the result here so next time people can use it as reference.