Troy Built varible speed

This mower moves really slow. The variable pulley moves up and down easy. I noticed that the bigger pulley next to it wobbles when spinning. Any clue why this would happen?

Pull the belt off the wobbly pulley then check the pulley is tight on the shaft.
The shaft itself is prone to failure.
Some of the pulleys are on a fine spline which has a tendency to strip out if the bolt gets a bit loose.