Motorcycle Petcocks

A petcock is simply the fuel valve that allows you to turn on or shut off the flow of gasoline from your gas tank to your carburetor. There are a number of different petcock sizes available. Late model Harley-Davidsons typically use a 22mm petcock, which are available in a variety of price ranges depending on the quality, fit and finish of the brand. The 22mm petcock bung is also found on some custom gas tanks such as the Narrow Frisco Sporty Gas Tank and the Blackbird Legacy Gas Tank for 1983-2003 Harley-Davidson Sportsters.

Many custom and aftermarket gas tanks such as the Narrow Alien Gas Tank and Super Narrow Frisco Mount Sportster Gas Tank also use a 1/4 inch NPT or 3/8 NPT petcock. NPT stands for National Pipe Thread, and it is a tapered thread that seals as you tighten the petcock into the threaded fitting on your gas tank. Lowbrow Customs also makes petcock adapter nuts in both brass and chrome and allow you to adapt your 22mm petcock bung to accept either a 1/4 inch NPT or 3/8 inch NPT petcock.

Standard petcocks have two positions: on and off. Some petcocks offer a Reserve function. A petcock that has reserve has a small tube inside the mesh filter that sits up higher than the bottom of your gas tank. If you have your petcock in the ON position while riding and your bike starts sputtering as you run out of gas, you can simply turn your petcock to the Reserve position and use the bit of reserve gasoline left in your tank to get somewhere and get fueled up. It gives a bit of peace of mind to those who are riding around with smaller gas tanks that they won’t be pushing their bike down the road in search of a gas station.