diagram for changing variable speed belt?

variable speed belt replacement diagram for an
MTD 1442 model # 133M660G513. Item tried is
part # 115 754-0280.
When tried the belt on it is still loose after clutch is let out, seems like it needs to be tighter. When clutch engaged the belt comes off of the the front motor pulley.
Would like to see diagram for the probper replacement to see how it fits. There is also a small idle pulley in the middle