I agree with trapper! I've seen them run on 60psi, I've no idea how though! General rule of thumb is 90psi or higher for a two stroke, 50psi or higher for a four stroke.
Little antidote, I had a buddy call me a while back, one of the best car mechanics I know, really knows his stuff! He was working on a lawn mower with a 6.75hp Kawi on it. He asks me how much compression it needs, he can get it to run, he says he can prime it and it runs, but not well.
I tell him what I stated above, he responds, "OH! That's not good, I've only got 35psi out of it!"
He pulled the head and the head gasket was blown. Odd and rare for these engines, but this thing had been abused, so nothing was surprising.
I just found it funny that someone who knows so much about cars couldn't relate the same knowledge to a small engine. Same thing, same rules, just smaller.