Originally Posted by old polaris tech

If it's any help in understanding how one carb can fit different machine,take the Polaris 250,300,400 atvs. Basically they can use the same diameter carb,but the jetting and jet needles are the main difference. When carbs say it's a 20 mm,22 mm,etc it's not in the external dimensions of the carb but in the open area called the venturi where the carb is measured.That's why it's possible for one size carb that can be used on several different models in engine cc size.Again the main difference is in the internal jetting sizes of the carb and also needle valves(needle and seats) have different flow rates depending on the machine it's used on. Some needle valves may have say a 1.5 gfm (gallon flow per minute) for a smaller engine versus a larger needle valve(2.0- 2.5 gfm for instance) to allow a faster fuel delivery to the carb bowl for a larger engine size. These are sometimes marked on the bottom of the needle valves. Here's a video on the venturi of a carb. Hope this helps.Test Prep (4) - The Carburetor Venturi and its Size Relationship with the Carburetor Intake Opening - YouTube