Clint,
its actually a matter of finding the right pressure for the material. there is a VAST array of needle and fluid tip designs. My minijet has the same size needle as my full size Kremlin but they take way different settings. WHat material you are spraying has a huge impact as well. What kind of problems are  you having, is it not atomozing, uneven pattern, not flowing out,, just what is wrong? If its for clear, my guess is that you are not thinning the product enough to get a good pattern and some thinner, plus perhaps a bit more air pressure will help. This is assuming you have a good gun, all the orifices are clean and I mean CLEAN. the tiniest bit of debri can totaly screw a gun up especially with clears.
how about some more info and perhaps I can give you more direct assistance?

Clint,
others have more experience with retarder than I do, I only have used it once.
it really sounds like your not getting your dope thin enough. I would suggest stepping on the clear a bit more, then perhaps bumping the air pressure a bit. Is your pressure gauge at the gun or at the compressor? Keep in mind that there is a HUGE pressure drop in an airhose, so ifyou set the pressure based upon a compressor mounted regulator, you are getting a false reading. There are charts online for figuring the pressure drop based upon hose ID and length.
Are you using the thinner for the clear that the manufacture reccomends? On really hot days, I will tend to reduce a bit more to get the clear to the surface while still containing enough solvent to allow flowing.
Really though based upon what your saying, it sounds like it is not atomizing, pretty much the two ways to affect that are, more air pressure, ( perhaps narrow the fan pattern adjust a little bit as well) then thin your clear a bit more.
Let me know if this helps

2000 grit wont really do much for orange peel texture. You really need to use more grit, I would say 800 would be as fine as I would go. The danger is that you dont have enough film thickness on there to really do much sanding without a HUGE risk of sanding through. If it were me, I would shoot a couple more coats on, then sand with 800 on a firm pad, ( or I like to use a section of paint stick with the paper wrapped TIGHTLY around it.)
I would NOT spray plain thinner on it. Perhaps a highly reduced coat, but I dont like that idea, with laquer you will saturate the undercoats with thinner that will take eons to dry out completely. Another note, before you sand to remove texture, make sure it dries for quite a while, say a week or better. Otherwise you will just be sanding again later when the solvents finish drying out after you sand it. SPeaking of, thats another tip for you. When you are letting something outgass, every day, or a couple times a day, lightly scuff the surface with some 600 or 800 paper to break the surface open, this allows the solvents to escape easier since they dont have to try escaping through the dry "shell" on the outside of the finish.

Here is a good website with some pretty solid information about pressure losses in air hoses. Another point it brings up is VOLUME, remember the Finex is an HVLP, High VOLUME low pressure gun. If it is not getting enough volume it will not atomize well regardless of the pressure. a 3/8 hose is the bare minimum on this gun IMHO. In fact its likely that your instructions reccomend a hose size, and perhaps even reccomend against certain styles of quick dissconnects since they tend to rob you of volume and flow.

http://www.pfonline.com/articles/0103qf1.html

Mark is spot on as usual. I would note one thing: when your setting the pressure at the regulator whether it's at the gun (better) or the compressor, hold the trigger of the gun down and look at the gauge. It should remain above the minimum setting. If not, dial it up until it does.