will not idle

hello i have a 87trx250r i bought from sombody and will not idle i manage to get it to kick cold on second kick but when let off throttle or push choke in shuts off. it runs 50-1 amsoil oil with 93 octane and has vforce delta 3 reeds thats about all i can tell ya. it wants to bog at 1/4 throttle but after that it screams some info would greatly appriciated thank you.