Need help solving this problem

Hi Rick, how about posting a piece about identifying coil problems, as we know they can be very fickle things.

 

Most of the Coil Death episodes all share the same complaint from the Owner who had one go South.

"My Bike was running fine; now it's missing and backfiring"

I don't even know what it is that breaks-down, yet.
The external connections, the Coil or the Spark Plug Wires.
Just that, now after a couple of decades or more, there is a spike in the occurrences of people having a Coil go out on them.

I think what I might do is slice one open and look inside for anything that looks funny.

Any guesses of what I might find in there?

 

The difficulty with identifying "coil problems" is that the symptoms caused by a bad coil(s) can also be, in many instances, the same as those caused by carb problems.

Except in rather exceptional circumstances or conditions (i.e. only runs poorly when it's wet, or very damp), coils are pretty simple, durable little beasts.

As long as their primary and secondary resistance readings are in spec:

Ignition Coils:

For all models except XJ700's and XJ900RK:

Primary (input): 2.5 ohms +/- 10%
= 2.25 ohms - 2.75 ohms

Secondary (output): 11K ohms +/- 20%
= 8,800 ohms - 13,200 ohms

For all XJ700 and XJ900RK models:

Primary (input): 2.7 ohms +/- 10%
= 2.43 ohms - 2.97 ohms

Secondary (output): 12K ohms +/- 20% (XJ700)
= 9,600 ohms - 14,400 ohms

Secondary (output): 13.2K ohms +/- 20% (XJ900RK)
= 10,560 ohms - 15,840 ohms


Then they are going to be happy (as long as they are also receiving close to 12V input on the primary side).

All of the above reisistance readings are taken at 68-degrees Farenheit, and on the secondary side, WITHOUT the spark plug caps installed.

It's also a wise and prudent action to check the resistance of each spark plug cap boot. They should be either 5K ohms or 10K ohms, depending on which model you have. And except for instances of extreme derivations from specifications, more important is the "sameness" of readings across different caps (much like with cylinder compression readings: the actual reading is not that important, but the variance between cylinders is).

Of course, you should make sure that whatever ohmeter that you are using is calibrated correctly before use. On analog style multimeters, the different resistance range setting do require a re-calibration of the meter to a zero reading.

 

Rick; What you'll find in there is exactly what the name implies, a coil of wire (probably quite a lot) wound into a cylinder with an iron bar in the middle. Probably "potted" into the plastic the way the plug wires are, or it could be filled with some sort of horrible, smelly toxic PCB-laden electronics component guts GOOP like a capacitor, but there will still be a coil of wire around a core. I'd wear safety glasses and rubber gloves, and use a bandsaw to cut it at an angle like a salami. Let us know what you find, please. I have my own theories as to what goes wrong, mostly due to my experiences with failed Lucas coils which are not made quite the same. It would be VERY interesting to carefully cut apart a failed one.

 

I don't think I'm going to go splitting-open a Coil now that I know that there's PCB's inside.
I've had enough exposure to PCB's.
If they're encapsulated in the Coil; they're staying there.
I'm not helping them escape.

 

I think the component most likely to break down would be the secondary winding.

 

SQLGuy had it right on the money. If you supply a coil with battery voltage -- with everything else hooked up -- and you break the circuit on the ground side, the ignition coil's magnetic field will collapse which will induce a current in the secondary winding. This is where the HV spark comes from.

A quick test for a coil (CAUTION: Risk of shock! Use caution.):

• Hook 12 volts to the coil's '+' terminal.
• Hook a test lead or coil wire from the coil's secondary side to a spark plug or spark gap tester gapped to whatever is specified for the ignition circuit you're testing.
• Ground the spark plug or spark gap tester to the battery's '-' terminal.
• Momentarily ground the coil by hooking a test lead from the battery's '-' terminal to the ignition coil's '-' terminal.

When you break the ground connection, a spark should jump the gap on your spark plug or spark gap tester.

I usually repeat this test several dozen times to build some heat in the coil to make sure it fires when it heats up.

(Here's the tool I use at work to test customer's coils.)

 

Well it's official, my one coil is dead.

Tested using a spare coil I had laying around (one meant for 2&3 so the plug wires are too short unfortunately) but i was able to get spark on the plugs.

So now my question is

Is there a way to lengthen/replace the wires? (It looks to be just one assembly)

Or I do have a spare 1&4 coil but the ends that attach to the plugs are broken off, if there a way to replace the ends?

 

Sure, they just unscrew from the wires.

 

Coil Surgery is possible.
It takes removing some material from the Coil.

Once you get the old wire pulled-out; you have to secure the new wire's end to the "Nail Head" within the Coil.
I soldered the end of a wound, wire-core, spark plug wire to the point exposed when the old wire is removed.

My write-up and photographs can be found here:

http://xjbikes.com/Forums/viewtopic/t=1 ... rgery.html

 

Got the bike running properly this afternoon, my thanks go to everyone for the helping me out!

Quite the confusing problem, tricked me a few times here and there but was finally able to sort it out.

Ended up using my spare coil w/the broken spark plug boots/ends since it was relatively easy to just put on new ends.

Thanks again!