clutch problems

in 99' my friend bought a 250 RM and had only put about 15 hours on it since. well the other day i bought it off him, after i started to ride it i noticed right away when you put it in gear the motor will die if you dont goose the gas as it starts to die, but will idle fine out of gear, if you have the bike out of gear and lean it from side to side as you roll it the motor will catch and turn over. does anyone know the cause of my problems, and what needs to be done?