The "Jet Needle" goes through the main jet, not the pilot. The stock Mikuni carb has a fuel pilot jet, air pilot screw adjustment, needle jet, jet needle, main fuel jet, main air jet. The main jet sits in the needle jet, and the jet needle goes down through this assembly.
The only adjustment you need to make should be the main fuel jet, and it sounds like you have been steered correctly on that. 300 to 310 will probably be about right. You might possibly need to turn the air pilots out to 2 turns, but 1.5 is a good start as stated previously.
This carb tuning is very simple, don't let it get over complicated.
Sudco has diagrams and parts lists if you would like to see the internal parts:
http://www.sudco.com/vmpart.html
http://www.sudco.com/Diagrams123/expvm.gif
This one is also essentially the same carb, just a better diagram:
http://www.sudco.com/Diagrams123/vm26-606.gif