I've had bouncing needles where the core was actualy broke and grabbing every few revolutions.
Most likely there is a kink in the cable housing that kind of holds the core back a little until the speed increases. It's not usually a speedo problem.
IMOP, I don't think a different type of lube is going to help matters. You need to straighten out the cable and core.
Why don't you pull the cable completely out, Wash it thouroughly, inspect cable and core, and then relube and reinstall. Watch the routing to make sure there are smooth bends and no kinks.
