Mark's son rides a 2003 YZ125 and has a question about the YamaLink lowering

By lowering the rear suspension how will this affect the cornering of a yz 125 2003. My son is 12 & 5'6 loves motocross.

For the 2003 we only make the 1.5" YamaLink, and depending on your son's weight or aggressiveness the 1.5" could be too much leverage for motocross. That's why we made the shorter YZ RACE version, but that only fits the 06 and newer. As for the forks most are raising them in the clamps at a starting point of about 4mm and adjusting up or down 1 or 2 mm based on personal preference.