my riding mower has 3 pulleys and one wider plastic pulley in middle , which i assume is the engage , disengage pulley or idler pulley. how does the belt go on these pulleys and on the idler pulley , i know one belt pulls all pulleys except the drive pulley is separate belt, but i cant get the belt to pull the blades after i put it on. , please help me. hows this belt go on , i need a diagram or someone to explain thank you.