Cylinders 3 and 4 out

I was riding today and noticed a sputtering sound and loss of power in my 81 XJ650H Maxim. It was running really well for the last few times I took it out, but today it started riding poorly so I took it to a parking lot and noticed the right exhaust pipe wasn't putting out nearly as much power to the exhaust coming out as the left. After turning it off, starting was very difficult and it needed a lot of throttle and died at idle.

I was near a friend's house, so I got a ride back to my house, got some tools and the bike still would only run on 1 and 2, despite the battery and charging system checking out fine with a voltometer. I tried making sure the leads were secure and working and they were all fine.

Would this be due to a faulty ignition coil? I'm thinking it is because the bike was running beautifully before, would start first press of the button from cold with no choke or anything and run very smoothly. If so, should I get a used one off of eBay, or is there a modern alternative? If this couldn't be the case, what should I do? I want to repair the bike myself if possible, I've done a lot of work so far all myself.

 

that's odd...did you check for spark on all cylinders?

 

Shouldn't be ignition-related. 1/4 and 2/3 are the cylinders that shark coils.

Off-hand, I can't think of too much that would cause a spontaneous loss of those two cylinders... unless someone shoved a potato or something into the right exhaust.