It could be the plug cap or wire to the plug also. It could also be low compression.
I took apart some of the connectors and cleaned them up since they were pretty badly corroded but no luck getting it started. I guess I'm spending an afternoon with the voltage tester.The system used is well proven and reliable
If anyone is still looking for a possible solution to 1 or 2 cylinders not firing one possible solution is a Vaccum leak. I confirmed this as I had the same issue. I removed the airbox, placed my hand over each opening of each carb, and the one not running was able to suck in fuel and fired right up. I also sprayed some carb cleaner on each boot and wahlah, fired right up. I will be purchasing 4 new boots and will post results. In conclusion, check for a Vaccum leak. All I see is replace the coils, clean the carbs for the 8th time, replace spark plugs, compression, plugs blah blah blah etc. Etc. Could be an easy fix with new boots.I ran into a bit of an odd problem this weekend. My #1 cylinder isn't firing. It's just shooting the unburned fuel out the exhaust. I switched plugs with another cylinder and it still did it. The coil runs another cylinder that's also working just fine. I'm baffled by this one. It's a Yamaha XJ650.
Exactly. My bike is 21 years old and they are old and cracked.Throw age in there and intake manifold leaking gets common on rubber parts.