TrepMan -- Here is Boyesen's definition of what they are and how they operate:
Reeds are one-way valves controlling the amount of air/fuel mixture entering the crankcase of your outboard engine, then sealing it in to prevent it from escaping. Every two-cycle outboard has them. But the stock reeds in your outboard have a single-stage design that limits their efficiency. That's why stock outboards often cough and sputter at idle, fail to deliver a good hole shot, feel boggy or lifeless under throttle application, burn too much fuel or lack top-end punch. Plus, standard reeds are made of metal. Should one break, it could cause extensive damage to your outboard.
Boyesen Power Reeds are different...and better! They feature a patented dual-stage design allowing our reeds to respond instantly to any change in air/fuel flow as you accelerate or back off the throttle. The result? A dramatic increase in efficiency and performance across the entire power band, from start-up to flat out!