i have a 82 datsun truck and it is not running right. the only way it will run is if i choke it about 1/2 way and it will idle but fast and if i adjust the idle screw down then it cuts in and out. i replaced the fuel pump and put a rebuilt carb on it. it could be a vacumm leak somewhere but i cant find nothing. anyone know what the problem might be. i really need to get this thing fixed fast.