To adjust the drive belt on Honda Lawn Mower HRR216K9VKA you need to look for to follow the given steps, 1. First you need to take out the grass clipping collector bag. 2. From the spark plug, disconnect the wire and keep it apart. 3. Near the mower deck rear wheels there will be the belt housing. Remove that and keep aside. 4. Now, with the screwdriver, turn the screw on the transmission pulley wheel in clockwise direction. 5. Test the tension on the belt by moving it through pulley. 6. Now after completion, set back the housing and spark plug wire.