Ignition Coil, Failure?

I assume this is an ignition coil issue. Only cylinders 1 & 3 are firing. All plugs are brand new. I just finished syncing the carbs, and am in the process of finding the fuel mixture sweet spot.

The strange part about this is that each coil has one cylinder firing, one not firing. So it's not simply one bad coil. Would this likely be an issue of both coils getting enough power? I'm a bit stumped over here.

 

When a coil dies, both holes will go cold, not just one. I'd check the carbs if the bike has been sitting a while (over winter), replace the plugs (even if they were new) or switch the plugs from the dead holes to the good ones. Wires are a bit trickier to change.

My first guess is that it sat over winter, you're trying to fire her up, and the carbs need a cleaning. My second guess is that the plugs or wires are bad. Check the resistance in the wires of coil 1 and then coil two by connecting the leads to a multi-meter each to one wire across a coil. I don't remember the resistance of hand, if it is an open circuit, you have a bad wire or cap.

I'd check those things first before thinking about changing coils. Has it run yet this year or did this just happen recently?

 

im very new to XJs...but doesnt one coil fire 1 & 3 and the other 2 & 4 ?Easy coil test is to simply swap the two 12 volt wires from the coil which 'works' to the coil which doesnt - if it still fires it aint your coils. Also do a resistance check from the end of both HT leads per coil - should read 11 ohms (plug cap removed).

 

I've disassembled and cleaned the carbs this spring. Using the multimeter, I'm not getting a circuit from one spark plug cap to another.

The bike did sit over the winter, but I've done what I can do get her back to optimal condition. She runs now, but obviously very poorly. I believe I had spark at all four earlier, but not in the past week.

Reading over some previous posts, you think it could be too rich? And how does one swap out the wires of the coils? I'm afraid to just yank it out, unless that's how it's done..

 

Actually, with the lack of a circuit, I imagine the richness of the mixture wouldn't matter..

 

Did you check to make sure the spark plug boots are tight on the wires?. A loose boot will give the condition you describe.

You might want to unscrew them and trim just a tiny bit off the end of the wire with you tin snips.

 

I think they mean to swap the input wires on the coil, not the spark plug wires. One coil does fire both plug wires at the same time, so if you're getting spark at one plug end and not another, I'd suspect the spark plug wire itself has broken or shorted out. They are permanatly affixed to the coil, but Chacal sells a device to splice a new plug wire onto a piece of the original wire, also some people have been succesful at cutting the coil open and attaching new plug wires.

 

I've tried to make sure the boot is tightly on the wire, to no avail. I think I'll try snipping a bit off the end of the wire, see if that helps.

 

if you swap the primary (12v) side coil wires, DO swap the leads to the plugs

 

Well, I don't see why I'd have to change the 12v side wires (I could very well be wrong). Since one plug on each side works fine, I would assume that connection is fine. Unless all the coil sends power through one plug before the rest is dumped through the second, in which case I could see that being an issue.

 

I snip the very end of the Plug Wire back a couple of mm's to get a clean end going for me on the end of the Plug Wire.

Then, I strip a short piece of multi-strand copper wire and twist it as tight as I can.
Cut the end clean.
Feed it in the end of the Spark Plug wire as far as you can get the copper wires to extend into the end of the Spart Plug Wire.

Using the wire cutters ...
Cut the end of the twisted wires flush with the Spark Plug wire.
This exercise will give you a renewed tight fit for screwing the Plug Cap back on the plug wire.

The troublesome part of this is:
Yamaha didn't leave a lot of slack on the ends of the Spark Plug Wires to allow them to be trimmed more than once or twice.

 

In general I would agree with you Pvt, but if the failure is but the one secondary wire, you would be mistaken. You can have a coil firing only one plug. This is were the tester (that is you) will need to pull all of the plugs and, after re-inserting the plugs back into the leads and laying them on the head, watch the spark dance. If no joy on the offending lines, do as Rick suggests and trim back the lead a bit. Corrosion in these lines is a common problem and will lead to your spark plug lines dropping out on you. Using a multimeter, check the resistance between the red and grey or orange wire (these are the primary leads) for the coils. 2-3 ohms is normal. Then ohm between the spark plug boots. You should see 11K between them. If the primary checks ok and the secondary doesn't, there is hope. The repair for bad lines is not that hard, just takes some time. Go to the links on our home page and navigate to the XJ How-To and DIY page. You will find an article there on how to rebuild your coils that will save you some bucks.