compression test question

My guage reads a bit low. Even on my freshly built yamaha xs650 engines I get 100 or so. LLeak down passes with flying colors on the guage. My slant has a slight rough idle and I could only get 100 psi or so on the guage. But with a leak down it was more than acceptable. So could be the reman. Holley 1920 on it. It's not real bad for roughness so I just kind of ignore it for now. Also have black plug on 6. Clean for half of the porcelain but black for the other half to the threads. Car doesn't seem to use oil. No smoke while dad follows me...float height is good. Kind of a mystery I haven't figured out yet that may also be related to my slight idle quirk.

So....I would leak down test anyways.