The carb comes with #300 needle and seat. I have always used that and it works very well, but you have to run a “T” on the fuel line just before the carb, straight through goes to carb, “T” goes back to the gas tank. Some will run a smaller (#180 or so) needle and seat in combination with a Dellorto fuel pump, which has a build in bypass, that way you can run a straight fuel line to the carb with no “T”. Different floats i.e. weight, will change the fuel level in the bowl, you can achieve the same by bending the taps on the arm, so again six of one half a dozen of the other.