Both coils bad? Naw. Can't be. Just bad wires?

Hey everyone,
My beloved 82 xj650j has broken down after a couple months of fun. It had some carb issues because I hadn't yet thoroughly gone through the process of setting valve clearance, bench synch, wet float set, manometer, etc etc. I knew there was probably a slight vacuum leak and that I needed to do everything correctly to get it perfect and was zeroing in on a weekend when I could do it all. Honest!
But then it just started running real bad and in a couple of days wouldn't even start anymore. But even though the carbs do need more attention, what I really have here is an ignition problem. But I'm a little confused because I took one of those little spark testers that you clamp on the plug and tested the spark. I'm not sure I have the sequence right but assuming the cylinder on the left is 1 and then 2, 3 and 4 as you go to the right, here's what happened.
I put the tester on #1 with the adjustable gap at about 1/4 inch. As soon as I turned on the key and the kill switch it sparked before I cranked. Then I cranked and nothing. Then when I turned the key off it sparked again. But I couldn't get it to repeat that action reliably. Sometimes it would spark and sometimes nothing, but never when I'm cranking it. #2 sparks nicely and right on time. #3 - nothing. #4 exactly like #1. I understand it would be really unusual for both coils to be bad. Could it just be wires? But then why did it deteriorate so suddenly. Fuse? I've tested the continuity and it seems fine, but ?
Just want to see if anyone has an idea of what to check next.
thanks everyone,
Scott

 

Check these first look at the connectors to the coils plastic ones, disconnest see of contacts are well loose fitting if so use small dykes to cinch ends down a bit to snug put lil die eletric grease in place, recconect. You fid do an ohms test right? should be 2.4 +/- a couple. On the .'4 side ofcourse. Good luck!

 

It might be that the spark tester is faulty. Try removing all the plugs from the head and reconnecting them into the plug caps. Ensure that all the plug bodies are touching the engine (completing the circuit and protecting the coils) then crank the engine and check each plug for a good spark.

It might not make any difference, but at least you will have a little more information. You can also swap plugs around to see if the problem moves with the plug.

As donovan says, check your connections. Check the connections to the ignition module, too.

 

and how many miles on the bike?

I'm not convinced it's electrical unless your battery is just flat or maybe the starter is drawing too much current for the ignition to fire.

I'd strongly suggest you check your valve clearances immediately; you may have come to the point where it won't run due to a few tight valves.

 

Since you have a tester there are specs for the primary and secondary sides of the coils. Ohm them out and see if you are in spec. You can also put a test light on the incoming wires to the coils. When cranking the light should flash. The coil gets charged and when the field collapses(no power in) that is when the high voltage spark is made and sent to the plugs. Although not as rapid of a failure I have had the resistors in the plug wire ends get corrosion on them. If you look in the cap you will see a slot for a regular screw driver remove the end don't loose the spring or resistor clean with fine grit sand paper and reassemble. Neither of these sound like the issue you are having. Charge the battery over night and test some more.

 

Troubleshooting procedure and operation theory for TCI ignition: http://xjbikes.com/Forums/viewtopic/p=274100.html

 

I used to be a maintenance electrician and I've fixed many a weird and wonderful electrical fault, so I know what I'm doing. So I can say that this is an excellent link, which I shall bookmark for later reference. Thank you, SQLGuy.

 

Well this really gives me a lot to work with! I really appreciate it. Thanks to all of you.
When I figure it out, I'll come back and post the results. Maybe it'll help someone else too.