Jets & Metering Rods

In simple terms, jets are small threaded plugs with a tiny metering orifice throughout it's center that control the amount of fuel entering the carburetor's venturi. They are considered delicate metering components usually made from brass.  The diameter of the main jet metering orifice determines the fuel flow rate, hence the slightest difference could alter the air-fuel ratio. Do your homework. The wrong jet size can ruin your engine.