my grandfather has a ms250, ever since he got it, it has been a bugger to start, half the time it would flood. a little while ago I did a rebuild for him, even after that it still wouldn't start, so i began experimenting with starting it, i found that the only way i could get it to start was, ONE pull full choke, then half choke. ONLY DO ONE PULL ON CHOKE even if it doesn't pop.
That works for that particular saw, every saw is different