Fuel Shutoff Valve Here are three different fuel shutoff valves that can be adapted to most antique tractors. In most cases, any one of the three will usually shut off the flow to the carburetor effectively. The valves and fuel line adaptors can usually be found at hardware stores or auto parts stores. I use the one with the red handle (¼" NPT) because it fits onto my sediment bulb on my John deere B. We recommend that no gasoline or all-fuel carburetor be left sitting with the fuel turned on. No one wants a crankcase full of gasoline, which can ruin the engine and is hazardous.