Some jets are pressed in,generally not to be messed with! Reference something as to what jets you are messing with. Main,needle,pilot(slow or idle) and some the ap(power or leak) are the main concerns. There are some with air jets and vents that do not get bothered,I do not recall a needle seat that does not come out,it IS the main. The brass that the main screws into sometimes is removable. Anytime you deal with unlike metals electrolysis will act like loctite and be a pain to loosen,overtightened brass can be a nightmare! Theses parts pop when they are loosened,sometimes in 2 pieces! Replace the float valve for general maintenance,once a year for confusions sake. It may look fine,but for a few bucks can save a nightmare!