China Vacuum Tap Valve Petcock Suppliers
Most older motorcycles have a three-position fuel petcock valve (known as a "petrol tap" in the UK) mounted on or nearby the fuel tank to control the supply of gasoline: on, off, and reserve.
The reserve position accesses the bottom portion of the fuel tank. Many older motorcycles lacked a fuel gauge, making reliance on a fuel reserve a relatively common experience. Most now have an automatic, vacuum operated petcock (that may include a prime position which bypasses vacuum operation and allows fuel to flow to the carburetor without the engine turning over).