Join Date: Feb 2009
Location: dunedin florida
they work on vacuum, inside if your reed there is a one way valve that lets air in but not out. under that are holes that go directly to your exhaust ports. so at high throttle openings or cruising the reeds are pressurized by exhaust gas, closing the system. when you chop the throttle the exhaust pressure suddenly drop's. using the Venturi effect the exhaust port sucks in air threw the reed valve from the airbox. if you start the bike and remove this hose, you can here it sucking at idle, the noise suddenly stops when revved. the mild pressure of the crankcase will not overcome the extreme pressures of the exhaust at the port.