The compression tests on my ZN700 when I first got it with only 1,054 miles on it was 178 in 3 cylinders and 180 in the 1. So, I would say 100 is way too low. Did you squirt some oil into the spark plug holes to see if had an effect on the compression? If it goes up with oil, it indicates the piston rings are worn. If the oil has no effect, the valves need attention.
1985 Kawasaki ZN700 Shaft, 4cyl
1989 Yamaha Venture Royale
2007 Yamaha Royal Star Venture