Well those are pretty much stock from the factory and are fine what you will be learning with. most use a 60 outer idle. Now for your answer some people use a smaller needle an seat to reduce the amount of fuel it can flow therefor you can get away with not running a return line. I dont use this. Others do. Slide is like the accelerator pump in a carb it controls the air flow over the carb nozzle a 40 as used in a rotax pulls more fuel when throttle is opened. under certain condittions hot an humid I may use a 55 slide on a tm but rarely a 60 reason being as there are different nozzels that also effect fuel flow. I believe 9mm is stock down to 5mm the shorter the leaner that is why I stated to go with a simple setup and work with that as you can get in over your head an it gets expensive. Hope this answered some of your questions.