I have an Exmark Metro HP (belt drive). The right side belt keeps riding up on the edge of the larger pulley located closest to the wheel. Without to much investigating it appears that the upper pulley is not aligned properly with the lower pulley (just a guess). I have attempted to increase the belt tension on this one side however the belt continues to ride up on the side of the larger pulley. This causes the mower to pull to the right side. Can you provide me with any ideas on what the cause might be?