Sizing Carburetor for New Air Filter..?

How do you size the carburetor when buying a custom air filter for any engine? I've heard people talking about 20mm carbs and stuff like that, but I'm a bit of a newbie and i don't know how to do that..suggestions??

Is it in the manual of the engine??
For the most part you just want to make sure the hole in the air filter is at least as big as the hole where air is entering the carb.. As long as that is OK, you should be fine..
Hey "jrzmac" thats exactly what I'm talking about, but I'm using a Honda Clone engine and i want to extend the carb out to the side and have a UNI air filter like that - that you clamp on. But i need to ORDER one so i have to check the size before i do..cept I don't know how to measure the size ..:confused: help?