Auto body repair & detailing: Auto Paint, gravity spray gun, mazda rx 7

Question
Before adjusting the gun higher it was splattering and leaving a rough finish like it had to much air. at one point it wascoming out like wisps of hair. Also, how do I fix the spots wher I am back down to the primer? When I sanded some imperfectuions it went right down to the surface primer. In other spots the paint is so hard the sanding block does nothing but scratch the surface. I basically have holes in the paintas well as pools of paint. Also, when I added the hardener, the shade of the paint changed and the color is uneven. I think I need to start over, but how?
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Followup To

Question -
My son and I are restoring a 1985 MAzda RX-7 and decided to paint the car. With our Home Depot Gravity spray gun and Hawthorne Rayflex Daytona Electric Blue we went to work. The first coat went on beautifully over our gray primer. The second caot with added hardener was a diaster. The paint initiall splattered and tehn ran when we adjusted the spray. Now I have blemishes that I can either not sand (as they are hardened drips and runs) or end up taking down to the primer. This car is a mess. How can I save the situation?

Answer -
The only way to remedy the situation is to wet sand the problem areas with 400 or 600 grit wet or dry. Make sure to use a sanding block to evenly sand away the paint. If the paint ran on you, the gun was adjusted too high and the paint strokes were not done evenly.

Answer
What kind of paint are you using? Is it a single stage. If it is, the gun you are using may have too small of a fluid tip. a single stage gun should be at least a 1.4 mm. Also if you do not reduce it properly it will gum up on you. Please send me back details about what products you are using.