Here is a helpful note I found on the internet several months ago.
"HVLP Spray Gun -
Please note: The gun mentioned below is no longer sold by Harbor Freight. It looks like they have replaced it with a similar gun that uses a little more air. I looked at one and the cap looks the same and I'll bet it sprays as good as the #38308 gun, but I haven't used it. I would like some feedback on it from anyone who has used it. It usually has a #43430 for the order number and is purple.
The Harbor Freight HVLP gun #38308 that did sell for anywhere from $40 to $70 (depending on the sale catalog) is a great gun to use for primers and will also do an excellent job with base color coats and high build clears. It is a good gun for the part time painter as it puts on enough paint to do a good job, but not as much as an expensive production gun does that will get us novices in trouble. This is not a gun a professional would use for overall paint jobs, but I know a lot of pros use this gun for panel repair and primers. So if you are a part time painter who probably paints his rod in pieces and you need a gun that doesn't consume a lot of air I can recommend this gun. I spray with a 5 hp single stage compressor. This is probably the bare minimum you can get away with for an overall paint job (car in one piece).
For high build primers (mixed in highest build form) you might want to order their 1.7 Tip Kit for the gun from their service dept. (the gun comes with a 1.4 tip).
No, I don't work for Harbor Freight, I just like to pass on a good thing when I know one and this is one case where a low cost item has great performance. The one bad thing about the gun is that the instructions are not very good, so I have made up the following instructions based on my experiences with the gun. Any feed back you have on the gun or these instructions is welcome. Sumner
Setting up and spraying with the Harbor Freight HVLP gun #38308
Pressure Adjustment: Open your compressor regulator up so there is plenty of air pressure in the line to the gun (I set mine to about 90 psi). Next set the regulator on the gun handle to 50 psi (what I use for DP40 and K36) with the trigger pulled and leave it set there. Close the valve at the bottom of the handle (on the gun, not the regulator) and then with the trigger pulled, open it to the point where the air volume starts to stay the same (just listen to it) and leave it there (it should be pretty far open at this point). I never mess with this after this unless I think it has been changed.
Note: On my two year old gun they say the maximum pressure is 60 psi. On my new gun it says 40 psi. Instead of the 50 psi above you might try 40 psi if your gun says 40 psi max.
Fan Adjustment: Next open the fluid volume control about 3 turns for starters (at the back of the gun). Close the fan control down (on the left side of the gun behind the nozzle) so when you spray you only get small round circle. With the gun about 6 to 8 inches from a test surface (I use the garage door or better yet some sheet rock, or masking paper) move the gun across the surface (about 6 to 8 inches from the surface) and pull the trigger. As you are moving turn the fan control until you get the desired fan shape/width (about 5-6 inches wide top to bottom oval shape for overall painting) (remember if you are spraying up and down on a surface you can change the nozzle at the front of the gun 90 deg. so the fan is horizontal).
Fluid Control: Next after getting the fan the right size continue spraying and adjust the fluid volume at the back of the gun for the final adjustment to get the fluid right for the gun speed (how fast you sweep it across the work). You want to be laying on the paint at a pretty good volume, but not causing runs at a normal gun sweep speed.
Changing the pressure to match spec sheets: Now you're ready to paint and with 50 psi at the handle the gun is spraying about 10 psi at the cap. If you want 5 psi at the cap put 25 at the handle regulator (8 psi = 40 psi, 7 psi= 35 psi, etc.). You can't actually see the pressure at the cap which is what the spec sheets are referring to. The gun is internally regulating the pressure down based on the inlet pressure. Some expensive guns have a gauge off the back of the handle that tells you the cap pressure and then they also have a regulator and gauge at the bottom of the handle like this gun that regulates the pressure into the gun.
Painting: Look at what your painting and the way the paint is going on the surface right behind the gun and adjust from there. For instance if you want to spray some small areas/parts you can turn the fan down to a small round size. You will also have to greatly shut the fluid volume down at the back of the gun (clockwise) at the same time to avoid runs. I usually turn the air pressure at the regulator on the handle down to around 25 to 35 psi to do spot work like this.
Proper Pressure: Remember you need a high air pressure (Set as the spec sheet calls for) so that you get proper atomization and so you can turn the volume up. The higher pressure will actually mean fewer runs since the atomization is better. This is not so critical with the primers, but you really need it with the sealer, base, and clear coats so you get good coverage without runs and with little orange peel.
Note: I'm not a professional painter, but the above is what works for me. If anyone else has anything they would like to add to the above or comment on please e-mail me."
I personally set the regulator on the handle of my gut @ 50psig and get great atomization and paint usage.