Can't find misfire

Couldn't wait, had to play with it. It turns out that I wasn't getting spark while cranking, so I just wired straight to the battery temporarily. I checked vacuum and I'm getting about 18" with the idle screw all the way out and with the mix to where I have the most vacuum. I went down the line and pulled the plug wires while running, and number six made no change in how it ran. I pulled the valve cover and both valves are moving, and I did my research and it is supposed to be 10 and 12. I put a compression tester on it and I'm getting a little under 100 psi in that cylinder while the rest are roughly all around either 120 or 150 (don't remember which). So, going with another old trick, I held a thing piece of paper (bubble wrap actually) close to the exhaust and it didn't show any sign of a burnt exhaust valve. Until I was right up to the pipe, it wan't to just blow it into my hand. Once I was about an inch or so away, it wasn't exactly sucking it in, but more blowing it back and forth. I'm not too sure, but I am leaning towards a burnt exhaust valve, and I really don't want to pull this engine apart. I will say, that when I got it I mentioned I wanted to adjust the valves so it would run right and be quiet, but the brother of the old lady I got it from told me not to because she had been running so long without doing it. She had driven the car for 15 years and 50K miles without ever having a valve adjustment done. Then three years ago it blew the head gasket and her husband fixed it and did God knows what else, but I know his work, and it's pretty terrible; kinda surprised it still runs after him working on it. So, unless there's anything else that someone can think of, I guess I get to do a valve job.