I don't know your model of mower but if it's anything like the system mine uses you will need to adjust the tension of the belt. The old belt you took off will have stretched over time and the new one you have put on will be slightly shorter, effectively putting it under tension and driving the blades straight away. With the mower turned OFF and KEY REMOVED for safety you will need to find the adjuster that moves the deck to allow the belt to be a little slack when not driving the blades, it should then tighten up only when the blades are engaged. (The flat side of the belt does not go against the pulleys, the v side does)
TMJ, October 2009
