Erattic cylinder firing

I have a problem that I am hoping someone can help me with. I bought this 83 XJ750 for a good friend of mine. It was running very ragged with #1 cylinder not firing. I was told when i bought the bike that the carbs needed cleaning.
Before pulling the carbs I decided to do some troubleshooting. I checked the pickups-Good, checked the primary side of the coils-Good, checked the secondary side of the coils- strange, or no readings. During the testing process the bike started running erratically. Initially, it was missing on #1 cylinder. Then it started running on #1 & 4 and was missing on #2 &3 cylinders. Then, back to #1 & 4 missing again, then #4 started firing and #1 was dead again.
I decided to go ahead and build the carbs and bench sync them to eliminate any question with them. I put them back on today and it started instantly and idles good. Before starting it I also changed out both coils with ones that read within specs. I am not too impressed with the looks of the HT wires but figured they would do to try it out.
It is still missing on #1 cylinder and the pipe occasionally starts to get warm but them quickly gets cold. I can hear it firing every now and then. I am certain that the carbs are clean and it is getting fuel. I have a very strong feeling the problem is in the ignition system.
has anyone had any problem with the CDI module being a problem like this? Had I not have already changed the coils I would be thinking that they were the problem. It is the fact that I was having the episodes with the cylinders firing erratically at first that makes me suspect of an ignition problem.
If anyone has any past experiences with a problem like this or suspect the cause of the problem I would appreciate hearing about it.

Thanks, Ed

 

Hi Ed!

Can't help with any of your problems but just wanted to say hello from another Hoosier. I live in Huntington, 25 miles west of Fort Wayne. Hope you get your problem solved.

Cheers,

Phil

 

each coil has two plug leads they both fire at the same time,if you feel it's the coil, swap the plug leads from that coil and if the problem follows the lead it could be the wire or cap
if it stays the same try some new plugs

 

Thanks Polock,

I knew about the engine having what is called the "wasted spark", but didn't actually think about changing the high tension leads to try and check the firing of the cylinder. It just seems strange that the firing of the cylinders was so erratic. Not at all what I am used to with my bike.
My thoughts were that the CDI box might possibly be bad, but thinking about what you are saying, the box just controls each individual coil rather than each individual cylinder? Hummmm. I will have to check it out and let you know.

Hi Phil,

Glad to hear from you.

Ed

 

try new plugs, when i first got my xj i got new plugs just for the hell of it and it ran fine for a few days then started doing exactly what you are talking about at the top of the page, so i took them out but left them conected to the wires and layed them on the cylinders and turned it over and only 2 were sparking and the other 2 were sparking only wheen they felt like it, so i put the 10 year old plugs back in and it ran fine, and still does today