2008 yamaha yz250f running problem?

started last week when bike had been getting hard to start and slowly loosing power i feel or think it was tryd ride her today and took lil while get her started and started riding it felt as if back brake was dragging but wasnt and went crank her and felt as if she was a 450 more compression then it should have so i pushed it back to the shop went show my dad and it had freed up and kept kicking and it fired back up but shortly after it just straight cuts off doesnt die down slowly nothing just cuts off it hasnt been idleing it would cut off if i let rpms go down low. i did a compression check on it before i tryd crank her today she read 90psi pep say thats good on furums for it. could it be the carb is dirty ? topend shot ? bottom end ? oil not getting where needs be getting ? valves mess with way it runs thought in only botherd cranking it? which i think its something makeing it hard to crank and not the valves out wack?