XS750 Suddenly Not Getting Spark In 3rd Cylinder

I recently picked up an XS750. After a new battery, and a little work it ran great for a couple days. It ran real strong and revved up great. I took it on a few rides and all seemed great. The last ride I took it on, it was running really well. I drove it back home and went inside for about 20 minutes. After about 20 minutes of sitting I came back outside to go another ride. It started up fine, but didn’t rev all that well, and when I would put it in gear, it was extremely underpowered and the fastest I could go was less than 10mph. I figured the battery just needed charged or something, and after a night of sitting it would run good in the morning. The next morning it wouldn’t even start, so I started checking spark in each cylinder. I found good spark in the first and second cylinder and found a really weak spark in the third cylinder, and then when I checked again a few minutes later, I found there was no spark at all in the third cylinder now (for those of you who aren’t familiar with xs750’s, they only have three cylinders.)

I checked the spark coil, and it seems good. I also checked the spark plug and the spark plug cap and they all check out. The only thing left I think are the points which I haven’t checked yet. I was just wondering if anyone had experienced anything similar or could help me out with this really sudden loss of spark in the third cylinder. Help and comments would be greatly appreciated, thanks so much.

1) download manual and read it. This site is specific to 400cc 2 cylinders. Would behoove you to repost on X's 600 forum or something specific to your bike, after you read manual
2) pics or it doesn't exist
3) you mention know test results. Voltage in battery. Ohms of resistance in coils. Absolutely check points if your bike has points. You don't mention year or model so another mystery
4) re read manual