[Sn00dles]

Been looking into getting a better carb for my coily sierra, and am looking for more detailed information.
What is the difference between the 3k and the 4k, what are the part numbers for each.
I have been looking at https://www.certifiedmachine.com/webstore for the parts because I'd rather spend the money for a good result, buy once cry once right? But I'm not actually sure what I need to buy, I would prefer to use the original air box if I can but if I need to buy the air filter kit as well I'm happy to. Some people have been saying that you only need to buy the carburettor and it bolts straight on and uses the old airbox fine. Is this true or is there a little extra effort required.

Please help!