Can using lead additive,harm motorcycles?

lead was in fuel to protect valves, they have since been redesigned and don't require the lead in fuel so there is no benefit, unless you are running something quite old and unmodified. the damage from leaded gas to unleaded setups was mainly to the cat converters, which most bikes don't have. if your bike is new enough to have a cat converter, your valves obviously don't need the additive.