OK, It will have a CDI unit. Very possible the CDI box is bad on that old of a bike, I know, I have both an 84 and 86 and both CDI boxes were dead. You will want to verify wiring correctness first. The CDI is under the tank and right behind the steering head (on the XT versions anyway). There is a black with white stripe wire going to the unit from the ignition switch and the handlebar kill switch. Unplug that to verify that it is not being held in the "KILL" mode. If you have a side stand switch, bypass it by following the wire to the bullet terminals that connect it to the main harness. Unplug the side stand wires, plug the main harness wires together to bypass. Many have already done this but since you are in the build process, you may have it connected.
The longer of the pigtails from the CDI goes to the stator. There is white plastic plug and two wires with bullet connectors. Verify they are plugged in correctly as to wire color and pins NOT corroded...
As to function, the red and green wires (may have a small colored sleeve instead of wire color itself to identify the wire) The green and red are the CDI charge wires as the CDI receives power to run from the CDI, not the battery, so battery is unimportant to spark on these models.
The orange wire on the short pigtail is the wire to the coil itself, verify that. The black wire on the short pigtail is ground to the main harness. Verify it is good. Verify you have a ground connection from the main harness attached to the frame and that the connection is clean and bright metal. Put a little grease on it to help keep rust away. I do not know where this ground it, but you should as you put it together. This ground is usually the only ground to the frame in the system. Also, the coil frame gets it ground from the frame, make sure the attachment point on the frame is clean and greased as well.
Further info, there are 3 versions of the CDI unit. An 8 wire unit, a 10 wire and an 11 wire unit. Let me know which you have. The 8 wire is the most basic and does not need the side stand or neutral switch inputs.
If none of the above will restore spark, we will need to verify continuity of the CDI charging coils and the Trigger coils plus measure the AC voltage generated when kicking briskly. I will get my schematic and give you detailed instructions on checking this. You will need a multimeter for this. A cheap digital meter will suffice as we are not looking for precise values, just close. The multimeter should have both an OHM setting and ac and dc volt settings. Probably get one for 20 dollars or so. (didn't notice where you are located).
Further info. If the above tests and subsequent tests do not reveal a problem, then the CDI is most likely at fault. I will have a couple of recomendations. If you have been following my posts you will already know them. I am not pushing anything, just recommending a "good" fix.
If you wish you can PM me directly as this has been hashed and re-hashed here many times and I can go directly to email if you wish, for faster response.
Finishing touches on 84 and 86 for Colorado Trip this summer. Both running well...
Last edited by steveloomis; 19 Nov 2013 at 14:46.
Reason: spelling fix