Hi: I am new to the forum and so glad I found it. I have a ZT1540 with Kohler motor. Not a complaint in the world. Bought new in 2004. Have replaced several belts over the years, and last year had to replace two spindles and 2 pulleys. Put new belt on and a new spring on the tensioner(whatever it is called) hooked up belt, and when clutch is engaged, blades sound good. Anykind of grass cutting and the blades slow down and almost to a stop. What did I miss? The pulleys are gravely the spindles are also. Belt is same type as before. Help!