Based on searches that I have done in the past in here - I've seen compression numbers ranging from 105 psi to 145 psi. I wouldn't trust my Harbor Freight gauge for accuracy, but anything north of 100 psi would normally be a motor that can be at least started. With my QT I ended up replacing the original top end out of precaution because the bike is almost 40 years old. $40 and 20 minutes. Once I had established a good compression, I chased down some fuel issues (had to use a clone carb). If it hasn't been done, you probably need to replace the crank seals. Easy job if you have the tools.
I've been down this path with other bikes (four strokes) and most recently with a QT50. There isn't much to these QTs and parts are accessible and relatively cheap. Lots of great info here: http://qt50.net/